Uniqueness validator.

src/Squidex.Domain.Apps.Core.Model/Schemas/Json/SchemaConverter.cs

@@ -7,7 +7,6 @@
 
 using System;
 using Newtonsoft.Json;
-using Squidex.Infrastructure;
 using Squidex.Infrastructure.Json;
 
 namespace Squidex.Domain.Apps.Core.Schemas.Json

src/Squidex.Domain.Apps.Core.Model/Schemas/NumberFieldProperties.cs

@@ -21,6 +21,8 @@ namespace Squidex.Domain.Apps.Core.Schemas
 
         public double? DefaultValue { get; set; }
 
+        public bool IsUnique { get; set; }
+
         public bool InlineEditable { get; set; }
 
         public NumberFieldEditor Editor { get; set; }

src/Squidex.Domain.Apps.Core.Model/Schemas/StringFieldProperties.cs

@@ -19,6 +19,8 @@ namespace Squidex.Domain.Apps.Core.Schemas
 
         public int? MaxLength { get; set; }
 
+        public bool IsUnique { get; set; }
+
         public bool InlineEditable { get; set; }
 
         public string DefaultValue { get; set; }

src/Squidex.Domain.Apps.Core.Operations/ValidateContent/ValidationContext.cs

@@ -10,13 +10,20 @@ using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Threading.Tasks;
 using Squidex.Infrastructure;
+using Squidex.Infrastructure.Queries;
 
 namespace Squidex.Domain.Apps.Core.ValidateContent
 {
+    public delegate Task<IReadOnlyList<Guid>> CheckContents(Guid schemaId, FilterNode filter);
+
+    public delegate Task<IReadOnlyList<IAssetInfo>> CheckAssets(IEnumerable<Guid> ids);
+
     public sealed class ValidationContext
     {
-        private readonly Func<IEnumerable<Guid>, Guid, Task<IReadOnlyList<Guid>>> checkContent;
+        private readonly Guid contentId;
-        private readonly Func<IEnumerable<Guid>, Task<IReadOnlyList<IAssetInfo>>> checkAsset;
+        private readonly Guid schemaId;
+        private readonly CheckContents checkContent;
+        private readonly CheckAssets checkAsset;
         private readonly ImmutableQueue<string> propertyPath;
 
         public ImmutableQueue<string> Path
@@ -24,18 +31,32 @@ namespace Squidex.Domain.Apps.Core.ValidateContent
             get { return propertyPath; }
         }
 
+        public Guid ContentId
+        {
+            get { return contentId; }
+        }
+
+        public Guid SchemaId
+        {
+            get { return schemaId; }
+        }
+
         public bool IsOptional { get; }
 
         public ValidationContext(
-            Func<IEnumerable<Guid>, Guid, Task<IReadOnlyList<Guid>>> checkContent,
+            Guid contentId,
-            Func<IEnumerable<Guid>, Task<IReadOnlyList<IAssetInfo>>> checkAsset)
+            Guid schemaId,
-            : this(checkContent, checkAsset, ImmutableQueue<string>.Empty, false)
+            CheckContents checkContent,
+            CheckAssets checkAsset)
+            : this(contentId, schemaId, checkContent, checkAsset, ImmutableQueue<string>.Empty, false)
         {
         }
 
         private ValidationContext(
-            Func<IEnumerable<Guid>, Guid, Task<IReadOnlyList<Guid>>> checkContent,
+            Guid contentId,
-            Func<IEnumerable<Guid>, Task<IReadOnlyList<IAssetInfo>>> checkAsset,
+            Guid schemaId,
+            CheckContents checkContent,
+            CheckAssets checkAsset,
             ImmutableQueue<string> propertyPath,
             bool isOptional)
         {
@@ -46,23 +67,26 @@ namespace Squidex.Domain.Apps.Core.ValidateContent
 
             this.checkContent = checkContent;
             this.checkAsset = checkAsset;
+            this.contentId = contentId;
+
+            this.schemaId = schemaId;
 
             IsOptional = isOptional;
         }
 
         public ValidationContext Optional(bool isOptional)
         {
-            return isOptional == IsOptional ? this : new ValidationContext(checkContent, checkAsset, propertyPath, isOptional);
+            return isOptional == IsOptional ? this : new ValidationContext(contentId, schemaId, checkContent, checkAsset, propertyPath, isOptional);
         }
 
         public ValidationContext Nested(string property)
         {
-            return new ValidationContext(checkContent, checkAsset, propertyPath.Enqueue(property), IsOptional);
+            return new ValidationContext(contentId, schemaId, checkContent, checkAsset, propertyPath.Enqueue(property), IsOptional);
         }
 
-        public Task<IReadOnlyList<Guid>> GetInvalidContentIdsAsync(IEnumerable<Guid> contentIds, Guid schemaId)
+        public Task<IReadOnlyList<Guid>> GetContentIdsAsync(Guid schemaId, FilterNode filter)
         {
-            return checkContent(contentIds, schemaId);
+            return checkContent(schemaId, filter);
         }
 
         public Task<IReadOnlyList<IAssetInfo>> GetAssetInfosAsync(IEnumerable<Guid> assetId)

src/Squidex.Domain.Apps.Core.Operations/ValidateContent/Validators/ReferencesValidator.cs

@@ -7,12 +7,16 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
+using Squidex.Infrastructure.Queries;
 
 namespace Squidex.Domain.Apps.Core.ValidateContent.Validators
 {
     public sealed class ReferencesValidator : IValidator
     {
+        private static readonly IReadOnlyList<string> Path = new List<string> { "Id" };
+
         private readonly Guid schemaId;
 
         public ReferencesValidator(Guid schemaId)
@@ -24,11 +28,16 @@ namespace Squidex.Domain.Apps.Core.ValidateContent.Validators
         {
             if (value is ICollection<Guid> contentIds)
             {
-                var invalidIds = await context.GetInvalidContentIdsAsync(contentIds, schemaId);
+                var filter = new FilterComparison(Path, FilterOperator.In, new FilterValue(contentIds.ToList()));
+
+                var foundIds = await context.GetContentIdsAsync(schemaId, filter);
 
-                foreach (var invalidId in invalidIds)
+                foreach (var id in contentIds)
                 {
-                    addError(context.Path, $"Contains invalid reference '{invalidId}'.");
+                    if (!foundIds.Contains(id))
+                    {
+                        addError(context.Path, $"Contains invalid reference '{id}'.");
+                    }
                 }
             }
         }

src/Squidex.Domain.Apps.Core.Operations/ValidateContent/Validators/UniqueValidator.cs

@@ -0,0 +1,51 @@
+// ==========================================================================
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex UG (haftungsbeschraenkt)
+//  All rights reserved. Licensed under the MIT license.
+// ==========================================================================
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Squidex.Infrastructure.Queries;
+
+namespace Squidex.Domain.Apps.Core.ValidateContent.Validators
+{
+    public sealed class UniqueValidator : IValidator
+    {
+        public async Task ValidateAsync(object value, ValidationContext context, AddError addError)
+        {
+            var count = context.Path.Count();
+
+            if (value != null && (count == 0 || (count == 2 && context.Path.Last() == InvariantPartitioning.Instance.Master.Key)))
+            {
+                FilterNode filter = null;
+
+                if (value is string s)
+                {
+                    filter = new FilterComparison(Path(context), FilterOperator.Equals, new FilterValue(s));
+                }
+                else if (value is double d)
+                {
+                    filter = new FilterComparison(Path(context), FilterOperator.Equals, new FilterValue(d));
+                }
+
+                if (filter != null)
+                {
+                    var found = await context.GetContentIdsAsync(context.SchemaId, filter);
+
+                    if (found.Any(x => x != context.ContentId))
+                    {
+                        addError(context.Path, "Another content with the same value exists.");
+                    }
+                }
+            }
+        }
+
+        private static List<string> Path(ValidationContext context)
+        {
+            return Enumerable.Repeat("Data", 1).Union(context.Path).ToList();
+        }
+    }
+}

src/Squidex.Domain.Apps.Core.Operations/ValidateContent/ValidatorsFactory.cs

@@ -111,6 +111,11 @@ namespace Squidex.Domain.Apps.Core.ValidateContent
             {
                 yield return new AllowedValuesValidator<double>(field.Properties.AllowedValues);
             }
+
+            if (field.Properties.IsUnique)
+            {
+                yield return new UniqueValidator();
+            }
         }
 
         public IEnumerable<IValidator> Visit(IField<ReferencesFieldProperties> field)
@@ -147,6 +152,11 @@ namespace Squidex.Domain.Apps.Core.ValidateContent
             {
                 yield return new AllowedValuesValidator<string>(field.Properties.AllowedValues);
             }
+
+            if (field.Properties.IsUnique)
+            {
+                yield return new UniqueValidator();
+            }
         }
 
         public IEnumerable<IValidator> Visit(IField<TagsFieldProperties> field)

src/Squidex.Domain.Apps.Entities.MongoDb/Contents/MongoContentCollection.cs

@@ -49,7 +49,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents
             {
                 query = query.AdjustToModel(schema.SchemaDef, useDraft);
 
-                var filter = FindExtensions.BuildQuery(query, schema.Id, status);
+                var filter = query.ToFilter(schema.Id, status);
 
                 var contentCount = Collection.Find(filter).CountDocumentsAsync();
                 var contentItems =

src/Squidex.Domain.Apps.Entities.MongoDb/Contents/MongoContentDraftCollection.cs

@@ -16,9 +16,11 @@ using Squidex.Domain.Apps.Core.ConvertContent;
 using Squidex.Domain.Apps.Entities.Apps;
 using Squidex.Domain.Apps.Entities.Contents;
 using Squidex.Domain.Apps.Entities.Contents.State;
+using Squidex.Domain.Apps.Entities.MongoDb.Contents.Visitors;
 using Squidex.Domain.Apps.Entities.Schemas;
 using Squidex.Infrastructure;
 using Squidex.Infrastructure.MongoDb;
+using Squidex.Infrastructure.Queries;
 using Squidex.Infrastructure.Reflection;
 using Squidex.Infrastructure.States;
 
@@ -52,13 +54,15 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents
             await base.SetupCollectionAsync(collection, ct);
         }
 
-        public async Task<IReadOnlyList<Guid>> QueryNotFoundAsync(Guid appId, Guid schemaId, IList<Guid> ids)
+        public async Task<IReadOnlyList<Guid>> QueryIdsAsync(Guid appId, ISchemaEntity schema, FilterNode filterNode)
         {
+            var filter = filterNode.AdjustToModel(schema.SchemaDef, true).ToFilter(schema.Id);
+
             var contentEntities =
-                await Collection.Find(x => x.IndexedSchemaId == schemaId && ids.Contains(x.Id) && x.IsDeleted != true).Only(x => x.Id)
+                await Collection.Find(filter).Only(x => x.Id)
                     .ToListAsync();
 
-            return ids.Except(contentEntities.Select(x => Guid.Parse(x["_id"].AsString))).ToList();
+            return contentEntities.Select(x => Guid.Parse(x["_id"].AsString)).ToList();
         }
 
         public async Task<IReadOnlyList<Guid>> QueryIdsAsync(Guid appId)

src/Squidex.Domain.Apps.Entities.MongoDb/Contents/MongoContentEntity.cs

@@ -24,7 +24,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents
         private NamedContentData dataDraft;
 
         [BsonId]
-        [BsonElement]
+        [BsonElement("_id")]
         [BsonRepresentation(BsonType.String)]
         public Guid Id { get; set; }
 

src/Squidex.Domain.Apps.Entities.MongoDb/Contents/MongoContentRepository.cs

@@ -91,11 +91,11 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents
             }
         }
 
-        public async Task<IReadOnlyList<Guid>> QueryNotFoundAsync(Guid appId, Guid schemaId, IList<Guid> ids)
+        public async Task<IReadOnlyList<Guid>> QueryIdsAsync(Guid appId, Guid schemaId, FilterNode filterNode)
         {
             using (Profiler.TraceMethod<MongoContentRepository>())
             {
-                return await contentsDraft.QueryNotFoundAsync(appId, schemaId, ids);
+                return await contentsDraft.QueryIdsAsync(appId, await appProvider.GetSchemaAsync(appId, schemaId), filterNode);
             }
         }
 

src/Squidex.Domain.Apps.Entities.MongoDb/Contents/Visitors/AdaptionVisitor.cs

@@ -0,0 +1,50 @@
+// ==========================================================================
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex UG (haftungsbeschränkt)
+//  All rights reserved. Licensed under the MIT license.
+// ==========================================================================
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NodaTime;
+using Squidex.Infrastructure.Queries;
+
+namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Visitors
+{
+    internal sealed class AdaptionVisitor : TransformVisitor
+    {
+        private readonly Func<IReadOnlyList<string>, IReadOnlyList<string>> pathConverter;
+
+        public AdaptionVisitor(Func<IReadOnlyList<string>, IReadOnlyList<string>> pathConverter)
+        {
+            this.pathConverter = pathConverter;
+        }
+
+        public override FilterNode Visit(FilterComparison nodeIn)
+        {
+            FilterComparison result;
+
+            var value = nodeIn.Rhs.Value;
+
+            if (value is Instant &&
+                !string.Equals(nodeIn.Lhs[0], "mt", StringComparison.OrdinalIgnoreCase) &&
+                !string.Equals(nodeIn.Lhs[0], "ct", StringComparison.OrdinalIgnoreCase))
+            {
+                result = new FilterComparison(pathConverter(nodeIn.Lhs), nodeIn.Operator, new FilterValue(value.ToString()));
+            }
+            else
+            {
+                result = new FilterComparison(pathConverter(nodeIn.Lhs), nodeIn.Operator, nodeIn.Rhs);
+            }
+
+            if (result.Lhs.Count == 1 && result.Lhs[0] == "_id" && result.Rhs.Value is List<Guid> guidList)
+            {
+                result = new FilterComparison(nodeIn.Lhs, nodeIn.Operator, new FilterValue(guidList.Select(x => x.ToString()).ToList()));
+            }
+
+            return result;
+        }
+    }
+}

src/Squidex.Domain.Apps.Entities.MongoDb/Contents/Visitors/FindExtensions.cs

@@ -11,7 +11,6 @@ using System.Linq;
 using System.Reflection;
 using MongoDB.Bson.Serialization.Attributes;
 using MongoDB.Driver;
-using NodaTime;
 using Squidex.Domain.Apps.Core.Contents;
 using Squidex.Domain.Apps.Core.GenerateEdmSchema;
 using Squidex.Domain.Apps.Core.Schemas;
@@ -28,33 +27,30 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Visitors
             typeof(MongoContentEntity).GetProperties()
                 .ToDictionary(x => x.Name, x => x.GetCustomAttribute<BsonElementAttribute>()?.ElementName ?? x.Name, StringComparer.OrdinalIgnoreCase);
 
-        private sealed class AdaptionVisitor : TransformVisitor
+        public static Query AdjustToModel(this Query query, Schema schema, bool useDraft)
         {
-            private readonly Func<IReadOnlyList<string>, IReadOnlyList<string>> pathConverter;
+            var pathConverter = PathConverter(schema, useDraft);
 
-            public AdaptionVisitor(Func<IReadOnlyList<string>, IReadOnlyList<string>> pathConverter)
+            if (query.Filter != null)
             {
-                this.pathConverter = pathConverter;
+                query.Filter = query.Filter.Accept(new AdaptionVisitor(pathConverter));
             }
 
-            public override FilterNode Visit(FilterComparison nodeIn)
+            query.Sort = query.Sort.Select(x => new SortNode(pathConverter(x.Path), x.SortOrder)).ToList();
-            {
-                var value = nodeIn.Rhs.Value;
 
-                if (value is Instant &&
+            return query;
-                    !string.Equals(nodeIn.Lhs[0], "mt", StringComparison.OrdinalIgnoreCase) &&
-                    !string.Equals(nodeIn.Lhs[0], "ct", StringComparison.OrdinalIgnoreCase))
-                {
-                    return new FilterComparison(pathConverter(nodeIn.Lhs), nodeIn.Operator, new FilterValue(value.ToString()));
         }
 
-                return new FilterComparison(pathConverter(nodeIn.Lhs), nodeIn.Operator, nodeIn.Rhs);
+        public static FilterNode AdjustToModel(this FilterNode filterNode, Schema schema, bool useDraft)
-            }
+        {
+            var pathConverter = PathConverter(schema, useDraft);
+
+            return filterNode.Accept(new AdaptionVisitor(pathConverter));
         }
 
-        public static Query AdjustToModel(this Query query, Schema schema, bool useDraft)
+        private static Func<IReadOnlyList<string>, IReadOnlyList<string>> PathConverter(Schema schema, bool useDraft)
         {
-            var pathConverter = new Func<IReadOnlyList<string>, IReadOnlyList<string>>(propertyNames =>
+            return new Func<IReadOnlyList<string>, IReadOnlyList<string>>(propertyNames =>
             {
                 var result = new List<string>(propertyNames);
 
@@ -96,15 +92,6 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Visitors
 
                 return result;
             });
-
-            if (query.Filter != null)
-            {
-                query.Filter = query.Filter.Accept(new AdaptionVisitor(pathConverter));
-            }
-
-            query.Sort = query.Sort.Select(x => new SortNode(pathConverter(x.Path), x.SortOrder)).ToList();
-
-            return query;
         }
 
         public static IFindFluent<MongoContentEntity, MongoContentEntity> ContentSort(this IFindFluent<MongoContentEntity, MongoContentEntity> cursor, Query query)
@@ -122,16 +109,16 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Visitors
             return cursor.Skip(query);
         }
 
-        public static FilterDefinition<MongoContentEntity> BuildQuery(Query query, Guid schemaId, Status[] status)
+        public static FilterDefinition<MongoContentEntity> ToFilter(this Query query, Guid schemaId, Status[] status)
         {
             var filters = new List<FilterDefinition<MongoContentEntity>>
             {
-                Filter.Eq(x => x.IndexedSchemaId, schemaId)
+                Filter.Eq(x => x.IndexedSchemaId, schemaId),
+                Filter.Ne(x => x.IsDeleted, true)
             };
 
             if (status != null)
             {
-                filters.Add(Filter.Ne(x => x.IsDeleted, true));
                 filters.Add(Filter.In(x => x.Status, status));
             }
 
@@ -149,14 +136,19 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Visitors
                 }
             }
 
-            if (filters.Count == 1)
+            return Filter.And(filters);
-            {
-                return filters[0];
         }
-            else
+
+        public static FilterDefinition<MongoContentEntity> ToFilter(this FilterNode filterNode, Guid schemaId)
+        {
+            var filters = new List<FilterDefinition<MongoContentEntity>>
             {
+                Filter.Eq(x => x.IndexedSchemaId, schemaId),
+                Filter.Ne(x => x.IsDeleted, true),
+                filterNode.BuildFilter<MongoContentEntity>()
+            };
+
             return Filter.And(filters);
         }
     }
-    }
 }

src/Squidex.Domain.Apps.Entities/Contents/ContentGrain.cs

@@ -62,7 +62,7 @@ namespace Squidex.Domain.Apps.Entities.Contents
                 case CreateContent createContent:
                     return CreateReturnAsync(createContent, async c =>
                     {
-                        var ctx = await CreateContext(c.AppId.Id, c.SchemaId.Id, () => "Failed to create content.");
+                        var ctx = await CreateContext(c.AppId.Id, c.SchemaId.Id, Guid.Empty, () => "Failed to create content.");
 
                         GuardContent.CanCreate(ctx.Schema, c);
 
@@ -105,7 +105,7 @@ namespace Squidex.Domain.Apps.Entities.Contents
                     {
                         try
                         {
-                            var ctx = await CreateContext(Snapshot.AppId.Id, Snapshot.SchemaId.Id, () => "Failed to change content.");
+                            var ctx = await CreateContext(Snapshot.AppId.Id, Snapshot.SchemaId.Id, Snapshot.Id, () => "Failed to change content.");
 
                             GuardContent.CanChangeContentStatus(ctx.Schema, Snapshot.IsPending, Snapshot.Status, c);
 
@@ -162,7 +162,7 @@ namespace Squidex.Domain.Apps.Entities.Contents
                 case DeleteContent deleteContent:
                     return UpdateAsync(deleteContent, async c =>
                     {
-                        var ctx = await CreateContext(Snapshot.AppId.Id, Snapshot.SchemaId.Id, () => "Failed to delete content.");
+                        var ctx = await CreateContext(Snapshot.AppId.Id, Snapshot.SchemaId.Id, Snapshot.Id, () => "Failed to delete content.");
 
                         GuardContent.CanDelete(ctx.Schema, c);
 
@@ -197,7 +197,7 @@ namespace Squidex.Domain.Apps.Entities.Contents
 
             if (!currentData.Equals(newData))
             {
-                var ctx = await CreateContext(Snapshot.AppId.Id, Snapshot.SchemaId.Id, () => "Failed to update content.");
+                var ctx = await CreateContext(Snapshot.AppId.Id, Snapshot.SchemaId.Id, Snapshot.Id, () => "Failed to update content.");
 
                 if (partial)
                 {
@@ -301,11 +301,10 @@ namespace Squidex.Domain.Apps.Entities.Contents
             return Snapshot.Apply(@event);
         }
 
-        private async Task<ContentOperationContext> CreateContext(Guid appId, Guid schemaId, Func<string> message)
+        private async Task<ContentOperationContext> CreateContext(Guid appId, Guid schemaId, Guid contentId, Func<string> message)
         {
             var operationContext =
-                await ContentOperationContext.CreateAsync(
+                await ContentOperationContext.CreateAsync(appId, schemaId, contentId,
-                    appId, schemaId,
                     appProvider, assetRepository, contentRepository, scriptEngine, message);
 
             return operationContext;

src/Squidex.Domain.Apps.Entities/Contents/ContentOperationContext.cs

@@ -7,7 +7,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 using Squidex.Domain.Apps.Core.Contents;
 using Squidex.Domain.Apps.Core.EnrichContent;
@@ -18,6 +17,7 @@ using Squidex.Domain.Apps.Entities.Assets.Repositories;
 using Squidex.Domain.Apps.Entities.Contents.Commands;
 using Squidex.Domain.Apps.Entities.Contents.Repositories;
 using Squidex.Domain.Apps.Entities.Schemas;
+using Squidex.Infrastructure.Queries;
 using Squidex.Infrastructure.Tasks;
 
 namespace Squidex.Domain.Apps.Entities.Contents
@@ -29,6 +29,8 @@ namespace Squidex.Domain.Apps.Entities.Contents
         private IScriptEngine scriptEngine;
         private ISchemaEntity schemaEntity;
         private IAppEntity appEntity;
+        private Guid contentId;
+        private Guid schemaId;
         private Func<string> message;
 
         public ISchemaEntity Schema
@@ -39,6 +41,7 @@ namespace Squidex.Domain.Apps.Entities.Contents
         public static async Task<ContentOperationContext> CreateAsync(
             Guid appId,
             Guid schemaId,
+            Guid contentId,
             IAppProvider appProvider,
             IAssetRepository assetRepository,
             IContentRepository contentRepository,
@@ -51,8 +54,10 @@ namespace Squidex.Domain.Apps.Entities.Contents
             {
                 appEntity = appEntity,
                 assetRepository = assetRepository,
+                contentId = contentId,
                 contentRepository = contentRepository,
                 message = message,
+                schemaId = schemaId,
                 schemaEntity = schemaEntity,
                 scriptEngine = scriptEngine
             };
@@ -106,7 +111,7 @@ namespace Squidex.Domain.Apps.Entities.Contents
 
         private ValidationContext CreateValidationContext()
         {
-            return new ValidationContext((contentIds, schemaId) => QueryContentsAsync(schemaId, contentIds), QueryAssetsAsync);
+            return new ValidationContext(contentId, schemaId, (sid, filterNode) => QueryContentsAsync(sid, filterNode), QueryAssetsAsync);
         }
 
         private async Task<IReadOnlyList<IAssetInfo>> QueryAssetsAsync(IEnumerable<Guid> assetIds)
@@ -114,9 +119,9 @@ namespace Squidex.Domain.Apps.Entities.Contents
             return await assetRepository.QueryAsync(appEntity.Id, new HashSet<Guid>(assetIds));
         }
 
-        private async Task<IReadOnlyList<Guid>> QueryContentsAsync(Guid schemaId, IEnumerable<Guid> contentIds)
+        private async Task<IReadOnlyList<Guid>> QueryContentsAsync(Guid filterSchemaId, FilterNode filterNode)
         {
-            return await contentRepository.QueryNotFoundAsync(appEntity.Id, schemaId, contentIds.ToList());
+            return await contentRepository.QueryIdsAsync(appEntity.Id, filterSchemaId, filterNode);
         }
     }
 }

src/Squidex.Domain.Apps.Entities/Contents/Repositories/IContentRepository.cs

@@ -23,7 +23,7 @@ namespace Squidex.Domain.Apps.Entities.Contents.Repositories
 
         Task<IResultList<IContentEntity>> QueryAsync(IAppEntity app, ISchemaEntity schema, Status[] status, Query query);
 
-        Task<IReadOnlyList<Guid>> QueryNotFoundAsync(Guid appId, Guid schemaId, IList<Guid> ids);
+        Task<IReadOnlyList<Guid>> QueryIdsAsync(Guid appId, Guid schemaId, FilterNode filterNode);
 
         Task<IContentEntity> FindContentAsync(IAppEntity app, ISchemaEntity schema, Status[] status, Guid id);
 

src/Squidex.Infrastructure.MongoDb/MongoDb/Queries/FilterBuilder.cs

@@ -26,10 +26,15 @@ namespace Squidex.Infrastructure.MongoDb.Queries
 
             if (query.Filter != null)
             {
-                return (FilterVisitor<T>.Visit(query.Filter), true);
+                return (query.Filter.BuildFilter<T>(), true);
             }
 
             return (null, false);
         }
+
+        public static FilterDefinition<T> BuildFilter<T>(this FilterNode filterNode)
+        {
+            return FilterVisitor<T>.Visit(filterNode);
+        }
     }
 }

src/Squidex/Areas/Api/Controllers/Schemas/Models/Fields/NumberFieldPropertiesDto.cs

@@ -37,6 +37,11 @@ namespace Squidex.Areas.Api.Controllers.Schemas.Models.Fields
         /// </summary>
         public double[] AllowedValues { get; set; }
 
+        /// <summary>
+        /// Indicates if the field value must be unique. Ignored for nested fields and localized fields.
+        /// </summary>
+        public bool IsUnique { get; set; }
+
         /// <summary>
         /// Indicates that the inline editor is enabled for this field.
         /// </summary>

src/Squidex/Areas/Api/Controllers/Schemas/Models/Fields/StringFieldPropertiesDto.cs

@@ -47,6 +47,11 @@ namespace Squidex.Areas.Api.Controllers.Schemas.Models.Fields
         /// </summary>
         public string[] AllowedValues { get; set; }
 
+        /// <summary>
+        /// Indicates if the field value must be unique. Ignored for nested fields and localized fields.
+        /// </summary>
+        public bool IsUnique { get; set; }
+
         /// <summary>
         /// Indicates that the inline editor is enabled for this field.
         /// </summary>

src/Squidex/app/features/schemas/pages/schema/types/number-validation.component.html

@@ -1,4 +1,15 @@
 <div [formGroup]="editForm">
+    <div class="form-group row" *ngIf="showUnique">
+        <div class="col-9 offset-3">
+            <div class="form-check">
+                <input class="form-check-input" type="checkbox" id="{{field.fieldId}}_fieldUnique" formControlName="isUnique" /> 
+                <label class="form-check-label" for="{{field.fieldId}}_fieldUnique">
+                    Unique
+                </label>
+            </div>
+        </div>
+    </div>
+
     <div class="form-group row">
         <div class="col-9 offset-3">
             <div class="form-check">

src/Squidex/app/features/schemas/pages/schema/types/number-validation.component.ts

@@ -10,7 +10,12 @@ import { FormControl, FormGroup } from '@angular/forms';
 import { Observable } from 'rxjs';
 import { map, startWith } from 'rxjs/operators';
 
-import { FieldDto, NumberFieldPropertiesDto } from '@app/shared';
+import {
+    FieldDto,
+    NumberFieldPropertiesDto,
+    RootFieldDto,
+    Types
+} from '@app/shared';
 
 @Component({
     selector: 'sqx-number-validation',
@@ -27,9 +32,18 @@ export class NumberValidationComponent implements OnInit {
     @Input()
     public properties: NumberFieldPropertiesDto;
 
+    public showUnique: boolean;
+
     public showDefaultValue: Observable<boolean>;
 
     public ngOnInit() {
+        this.showUnique = Types.is(this.field, RootFieldDto) && !this.field.isLocalizable;
+
+        if (this.showUnique) {
+            this.editForm.setControl('isUnique',
+                new FormControl(this.properties.isUnique));
+        }
+
         this.editForm.setControl('maxValue',
             new FormControl(this.properties.maxValue));
 

src/Squidex/app/features/schemas/pages/schema/types/string-validation.component.html

@@ -1,4 +1,15 @@
 <div [formGroup]="editForm">
+    <div class="form-group row" *ngIf="showUnique">
+        <div class="col-9 offset-3">
+            <div class="form-check">
+                <input class="form-check-input" type="checkbox" id="{{field.fieldId}}_fieldUnique" formControlName="isUnique" /> 
+                <label class="form-check-label" for="{{field.fieldId}}_fieldUnique">
+                    Unique
+                </label>
+            </div>
+        </div>
+    </div>
+    
     <div class="form-group row">
         <div class="col-9 offset-3">
             <div class="form-check">

src/Squidex/app/features/schemas/pages/schema/types/string-validation.component.ts

@@ -15,7 +15,9 @@ import {
     FieldDto,
     ImmutableArray,
     ModalModel,
-    StringFieldPropertiesDto
+    RootFieldDto,
+    StringFieldPropertiesDto,
+    Types
 } from '@app/shared';
 
 @Component({
@@ -45,11 +47,20 @@ export class StringValidationComponent implements OnDestroy, OnInit {
     public patternName: string;
     public patternsModal = new ModalModel();
 
+    public showUnique: boolean;
+
     public ngOnDestroy() {
         this.patternSubscription.unsubscribe();
     }
 
     public ngOnInit() {
+        this.showUnique = Types.is(this.field, RootFieldDto) && !this.field.isLocalizable;
+
+        if (this.showUnique) {
+            this.editForm.setControl('isUnique',
+                new FormControl(this.properties.isUnique));
+        }
+
         this.editForm.setControl('maxLength',
             new FormControl(this.properties.maxLength));
 

src/Squidex/app/shared/services/schemas.types.ts

@@ -241,6 +241,7 @@ export class NumberFieldPropertiesDto extends FieldPropertiesDto {
     public readonly fieldType = 'Number';
 
     public readonly inlineEditable: boolean = false;
+    public readonly isUnique: boolean = false;
     public readonly defaultValue?: number;
     public readonly maxValue?: number;
     public readonly minValue?: number;
@@ -279,6 +280,7 @@ export class StringFieldPropertiesDto extends FieldPropertiesDto {
     public readonly fieldType = 'String';
 
     public readonly inlineEditable = false;
+    public readonly isUnique: boolean = false;
     public readonly defaultValue?: string;
     public readonly pattern?: string;
     public readonly patternMessage?: string;

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/ArrayFieldTests.cs

@@ -48,7 +48,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_tags_are_required_and_null()
+        public async Task Should_add_error_if_tags_are_required_and_null()
         {
             var sut = Field(new ArrayFieldProperties { IsRequired = true });
 
@@ -59,7 +59,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_tags_are_required_and_empty()
+        public async Task Should_add_error_if_tags_are_required_and_empty()
         {
             var sut = Field(new ArrayFieldProperties { IsRequired = true });
 
@@ -70,7 +70,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new ArrayFieldProperties());
 
@@ -81,7 +81,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_not_enough_items()
+        public async Task Should_add_error_if_value_has_not_enough_items()
         {
             var sut = Field(new ArrayFieldProperties { MinItems = 3 });
 
@@ -92,7 +92,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_too_much_items()
+        public async Task Should_add_error_if_value_has_too_much_items()
         {
             var sut = Field(new ArrayFieldProperties { MaxItems = 1 });
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/AssetsFieldTests.cs

@@ -93,7 +93,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_assets_are_required_and_null()
+        public async Task Should_add_error_if_assets_are_required_and_null()
         {
             var sut = Field(new AssetsFieldProperties { IsRequired = true });
 
@@ -104,7 +104,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_assets_are_required_and_empty()
+        public async Task Should_add_error_if_assets_are_required_and_empty()
         {
             var sut = Field(new AssetsFieldProperties { IsRequired = true });
 
@@ -115,7 +115,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new AssetsFieldProperties());
 
@@ -126,7 +126,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_not_enough_items()
+        public async Task Should_add_error_if_value_has_not_enough_items()
         {
             var sut = Field(new AssetsFieldProperties { MinItems = 3 });
 
@@ -137,7 +137,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_too_much_items()
+        public async Task Should_add_error_if_value_has_too_much_items()
         {
             var sut = Field(new AssetsFieldProperties { MaxItems = 1 });
 
@@ -148,7 +148,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_asset_are_not_valid()
+        public async Task Should_add_error_if_asset_are_not_valid()
         {
             var assetId = Guid.NewGuid();
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/BooleanFieldTests.cs

@@ -47,7 +47,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_boolean_is_required()
+        public async Task Should_add_error_if_boolean_is_required()
         {
             var sut = Field(new BooleanFieldProperties { IsRequired = true });
 
@@ -58,7 +58,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new BooleanFieldProperties());
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/DateTimeFieldTests.cs

@@ -39,7 +39,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_datetime_is_required()
+        public async Task Should_add_error_if_datetime_is_required()
         {
             var sut = Field(new DateTimeFieldProperties { IsRequired = true });
 
@@ -50,7 +50,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_datetime_is_less_than_min()
+        public async Task Should_add_error_if_datetime_is_less_than_min()
         {
             var sut = Field(new DateTimeFieldProperties { MinValue = FutureDays(10) });
 
@@ -61,7 +61,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_datetime_is_greater_than_max()
+        public async Task Should_add_error_if_datetime_is_greater_than_max()
         {
             var sut = Field(new DateTimeFieldProperties { MaxValue = FutureDays(10) });
 
@@ -72,7 +72,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new DateTimeFieldProperties());
 
@@ -83,7 +83,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_another_type()
+        public async Task Should_add_error_if_value_is_another_type()
         {
             var sut = Field(new DateTimeFieldProperties());
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/GeolocationFieldTests.cs

@@ -51,7 +51,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_geolocation_has_invalid_latitude()
+        public async Task Should_add_error_if_geolocation_has_invalid_latitude()
         {
             var sut = Field(new GeolocationFieldProperties { IsRequired = true });
 
@@ -66,7 +66,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_geolocation_has_invalid_longitude()
+        public async Task Should_add_error_if_geolocation_has_invalid_longitude()
         {
             var sut = Field(new GeolocationFieldProperties { IsRequired = true });
 
@@ -81,7 +81,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_geolocation_has_too_many_properties()
+        public async Task Should_add_error_if_geolocation_has_too_many_properties()
         {
             var sut = Field(new GeolocationFieldProperties { IsRequired = true });
 
@@ -97,7 +97,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_geolocation_is_required()
+        public async Task Should_add_error_if_geolocation_is_required()
         {
             var sut = Field(new GeolocationFieldProperties { IsRequired = true });
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/JsonFieldTests.cs

@@ -37,7 +37,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_json_is_required()
+        public async Task Should_add_error_if_json_is_required()
         {
             var sut = Field(new JsonFieldProperties { IsRequired = true });
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/NumberFieldTests.cs

@@ -5,6 +5,7 @@
 //  All rights reserved. Licensed under the MIT license.
 // ==========================================================================
 
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -38,7 +39,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_number_is_required()
+        public async Task Should_add_error_if_number_is_required()
         {
             var sut = Field(new NumberFieldProperties { IsRequired = true });
 
@@ -49,7 +50,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_number_is_less_than_min()
+        public async Task Should_add_error_if_number_is_less_than_min()
         {
             var sut = Field(new NumberFieldProperties { MinValue = 10 });
 
@@ -60,7 +61,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_number_is_greater_than_max()
+        public async Task Should_add_error_if_number_is_greater_than_max()
         {
             var sut = Field(new NumberFieldProperties { MaxValue = 10 });
 
@@ -71,7 +72,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_number_is_not_allowed()
+        public async Task Should_add_error_if_number_is_not_allowed()
         {
             var sut = Field(new NumberFieldProperties { AllowedValues = ReadOnlyCollection.Create(10d) });
 
@@ -82,7 +83,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new NumberFieldProperties());
 
@@ -92,6 +93,17 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
                 new[] { "Not a valid value." });
         }
 
+        [Fact]
+        public async Task Should_add_error_if_unique_constraint_failed()
+        {
+            var sut = Field(new NumberFieldProperties { IsUnique = true });
+
+            await sut.ValidateAsync(CreateValue(12.5), errors, ValidationTestExtensions.References(Guid.NewGuid()));
+
+            errors.Should().BeEquivalentTo(
+                new[] { "Another content with the same value exists." });
+        }
+
         private static JValue CreateValue(object v)
         {
             return new JValue(v);

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/ReferencesFieldTests.cs

@@ -20,6 +20,8 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
     {
         private readonly List<string> errors = new List<string>();
         private readonly Guid schemaId = Guid.NewGuid();
+        private readonly Guid ref1 = Guid.NewGuid();
+        private readonly Guid ref2 = Guid.NewGuid();
 
         [Fact]
         public void Should_instantiate_field()
@@ -34,7 +36,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         {
             var sut = Field(new ReferencesFieldProperties());
 
-            await sut.ValidateAsync(CreateValue(Guid.NewGuid()), errors, ValidationTestExtensions.ValidContext);
+            await sut.ValidateAsync(CreateValue(ref1), errors, ValidationTestExtensions.References(ref1));
 
             Assert.Empty(errors);
         }
@@ -50,7 +52,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_references_are_required_and_null()
+        public async Task Should_add_error_if_references_are_required_and_null()
         {
             var sut = Field(new ReferencesFieldProperties { SchemaId = schemaId, IsRequired = true });
 
@@ -61,7 +63,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_references_are_required_and_empty()
+        public async Task Should_add_error_if_references_are_required_and_empty()
         {
             var sut = Field(new ReferencesFieldProperties { SchemaId = schemaId, IsRequired = true });
 
@@ -72,7 +74,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new ReferencesFieldProperties());
 
@@ -83,38 +85,36 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_not_enough_items()
+        public async Task Should_add_error_if_value_has_not_enough_items()
         {
             var sut = Field(new ReferencesFieldProperties { SchemaId = schemaId, MinItems = 3 });
 
-            await sut.ValidateAsync(CreateValue(Guid.NewGuid(), Guid.NewGuid()), errors);
+            await sut.ValidateAsync(CreateValue(ref1, ref2), errors, ValidationTestExtensions.References(ref1, ref2));
 
             errors.Should().BeEquivalentTo(
                 new[] { "Must have at least 3 item(s)." });
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_too_much_items()
+        public async Task Should_add_error_if_value_has_too_much_items()
         {
             var sut = Field(new ReferencesFieldProperties { SchemaId = schemaId, MaxItems = 1 });
 
-            await sut.ValidateAsync(CreateValue(Guid.NewGuid(), Guid.NewGuid()), errors);
+            await sut.ValidateAsync(CreateValue(ref1, ref2), errors, ValidationTestExtensions.References(ref1, ref2));
 
             errors.Should().BeEquivalentTo(
                 new[] { "Must have not more than 1 item(s)." });
         }
 
         [Fact]
-        public async Task Should_add_errors_if_reference_are_not_valid()
+        public async Task Should_add_error_if_reference_are_not_valid()
         {
-            var referenceId = Guid.NewGuid();
-
             var sut = Field(new ReferencesFieldProperties { SchemaId = schemaId });
 
-            await sut.ValidateAsync(CreateValue(referenceId), errors, ValidationTestExtensions.InvalidReferences(referenceId));
+            await sut.ValidateAsync(CreateValue(ref1), errors, ValidationTestExtensions.References());
 
             errors.Should().BeEquivalentTo(
-                new[] { $"Contains invalid reference '{referenceId}'." });
+                new[] { $"Contains invalid reference '{ref1}'." });
         }
 
         private static JToken CreateValue(params Guid[] ids)

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/StringFieldTests.cs

@@ -5,6 +5,7 @@
 //  All rights reserved. Licensed under the MIT license.
 // ==========================================================================
 
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -38,7 +39,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_string_is_required()
+        public async Task Should_add_error_if_string_is_required()
         {
             var sut = Field(new StringFieldProperties { IsRequired = true });
 
@@ -49,7 +50,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_string_is_shorter_than_min_length()
+        public async Task Should_add_error_if_string_is_shorter_than_min_length()
         {
             var sut = Field(new StringFieldProperties { MinLength = 10 });
 
@@ -60,7 +61,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_string_is_longer_than_max_length()
+        public async Task Should_add_error_if_string_is_longer_than_max_length()
         {
             var sut = Field(new StringFieldProperties { MaxLength = 5 });
 
@@ -71,7 +72,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_string_not_allowed()
+        public async Task Should_add_error_if_string_not_allowed()
         {
             var sut = Field(new StringFieldProperties { AllowedValues = ReadOnlyCollection.Create("Foo") });
 
@@ -82,7 +83,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_number_is_not_valid_pattern()
+        public async Task Should_add_error_if_number_is_not_valid_pattern()
         {
             var sut = Field(new StringFieldProperties { Pattern = "[0-9]{3}" });
 
@@ -93,7 +94,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_number_is_not_valid_pattern_with_message()
+        public async Task Should_add_error_if_number_is_not_valid_pattern_with_message()
         {
             var sut = Field(new StringFieldProperties { Pattern = "[0-9]{3}", PatternMessage = "Custom Error Message." });
 
@@ -103,6 +104,17 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
                 new[] { "Custom Error Message." });
         }
 
+        [Fact]
+        public async Task Should_add_error_if_unique_constraint_failed()
+        {
+            var sut = Field(new StringFieldProperties { IsUnique = true });
+
+            await sut.ValidateAsync(CreateValue("abc"), errors, ValidationTestExtensions.References(Guid.NewGuid()));
+
+            errors.Should().BeEquivalentTo(
+                new[] { "Another content with the same value exists." });
+        }
+
         private static JValue CreateValue(object v)
         {
             return new JValue(v);

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/TagsFieldTests.cs

@@ -49,7 +49,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_tags_are_required_and_null()
+        public async Task Should_add_error_if_tags_are_required_and_null()
         {
             var sut = Field(new TagsFieldProperties { IsRequired = true });
 
@@ -60,7 +60,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_tags_are_required_and_empty()
+        public async Task Should_add_error_if_tags_are_required_and_empty()
         {
             var sut = Field(new TagsFieldProperties { IsRequired = true });
 
@@ -71,7 +71,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_is_not_valid()
+        public async Task Should_add_error_if_value_is_not_valid()
         {
             var sut = Field(new TagsFieldProperties());
 
@@ -82,7 +82,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_not_enough_items()
+        public async Task Should_add_error_if_value_has_not_enough_items()
         {
             var sut = Field(new TagsFieldProperties { MinItems = 3 });
 
@@ -93,7 +93,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_has_too_much_items()
+        public async Task Should_add_error_if_value_has_too_much_items()
         {
             var sut = Field(new TagsFieldProperties { MaxItems = 1 });
 
@@ -104,7 +104,7 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         }
 
         [Fact]
-        public async Task Should_add_errors_if_value_contains_an_not_allowed_values()
+        public async Task Should_add_error_if_value_contains_an_not_allowed_values()
         {
             var sut = Field(new TagsFieldProperties { AllowedValues = ReadOnlyCollection.Create("tag-2", "tag-3") });
 

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/ValidationTestExtensions.cs

@@ -18,10 +18,10 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
 {
     public static class ValidationTestExtensions
     {
-        private static readonly Task<IReadOnlyList<Guid>> ValidReferences = Task.FromResult<IReadOnlyList<Guid>>(new List<Guid>());
+        private static readonly Task<IReadOnlyList<Guid>> EmptyReferences = Task.FromResult<IReadOnlyList<Guid>>(new List<Guid>());
-        private static readonly Task<IReadOnlyList<IAssetInfo>> ValidAssets = Task.FromResult<IReadOnlyList<IAssetInfo>>(new List<IAssetInfo>());
+        private static readonly Task<IReadOnlyList<IAssetInfo>> EmptyAssets = Task.FromResult<IReadOnlyList<IAssetInfo>>(new List<IAssetInfo>());
 
-        public static readonly ValidationContext ValidContext = new ValidationContext((x, y) => ValidReferences, x => ValidAssets);
+        public static readonly ValidationContext ValidContext = new ValidationContext(Guid.NewGuid(), Guid.NewGuid(), (x, y) => EmptyReferences, x => EmptyAssets);
 
         public static Task ValidateAsync(this IValidator validator, object value, IList<string> errors, ValidationContext context = null)
         {
@@ -75,14 +75,14 @@ namespace Squidex.Domain.Apps.Core.Operations.ValidateContent
         {
             var actual = Task.FromResult<IReadOnlyList<IAssetInfo>>(assets.ToList());
 
-            return new ValidationContext((x, y) => ValidReferences, x => actual);
+            return new ValidationContext(Guid.NewGuid(), Guid.NewGuid(), (x, y) => EmptyReferences, x => actual);
         }
 
-        public static ValidationContext InvalidReferences(Guid referencesIds)
+        public static ValidationContext References(params Guid[] referencesIds)
         {
-            var actual = Task.FromResult<IReadOnlyList<Guid>>(new List<Guid> { referencesIds });
+            var actual = Task.FromResult<IReadOnlyList<Guid>>(referencesIds.ToList());
 
-            return new ValidationContext((x, y) => actual, x => ValidAssets);
+            return new ValidationContext(Guid.NewGuid(), Guid.NewGuid(), (x, y) => actual, x => EmptyAssets);
         }
     }
 }

tests/Squidex.Domain.Apps.Core.Tests/Operations/ValidateContent/Validators/UniqueValidatorTests.cs

@@ -0,0 +1,93 @@
+// ==========================================================================
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex UG (haftungsbeschraenkt)
+//  All rights reserved. Licensed under the MIT license.
+// ==========================================================================
+
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Squidex.Domain.Apps.Core.ValidateContent;
+using Squidex.Domain.Apps.Core.ValidateContent.Validators;
+using Xunit;
+
+namespace Squidex.Domain.Apps.Core.Operations.ValidateContent.Validators
+{
+    public class UniqueValidatorTests
+    {
+        private readonly List<string> errors = new List<string>();
+        private readonly Guid contentId = Guid.NewGuid();
+        private readonly Guid schemaId = Guid.NewGuid();
+
+        [Fact]
+        public async Task Should_add_error_if_string_value_not_found()
+        {
+            var sut = new UniqueValidator();
+
+            var filter = string.Empty;
+
+            await sut.ValidateAsync("hi", errors, Context(Guid.NewGuid(), f => filter = f));
+
+            errors.Should().BeEquivalentTo(
+                new[] { "property: Another content with the same value exists." });
+
+            Assert.Equal("Data.property.iv == 'hi'", filter);
+        }
+
+        [Fact]
+        public async Task Should_add_error_if_double_value_not_found()
+        {
+            var sut = new UniqueValidator();
+
+            var filter = string.Empty;
+
+            await sut.ValidateAsync(12.5, errors, Context(Guid.NewGuid(), f => filter = f));
+
+            errors.Should().BeEquivalentTo(
+                new[] { "property: Another content with the same value exists." });
+
+            Assert.Equal("Data.property.iv == 12.5", filter);
+        }
+
+        [Fact]
+        public async Task Should_not_add_error_if_string_value_found()
+        {
+            var sut = new UniqueValidator();
+
+            var filter = string.Empty;
+
+            await sut.ValidateAsync("hi", errors, Context(contentId, f => filter = f));
+
+            Assert.Empty(errors);
+        }
+
+        [Fact]
+        public async Task Should_not_add_error_if_double_value_found()
+        {
+            var sut = new UniqueValidator();
+
+            var filter = string.Empty;
+
+            await sut.ValidateAsync(12.5, errors, Context(contentId, f => filter = f));
+
+            Assert.Empty(errors);
+        }
+
+        private ValidationContext Context(Guid id, Action<string> filter)
+        {
+            return new ValidationContext(contentId, schemaId,
+                (schema, filterNode) =>
+                {
+                    filter(filterNode.ToString());
+
+                    return Task.FromResult<IReadOnlyList<Guid>>(new List<Guid> { id });
+                },
+                ids =>
+                {
+                    return Task.FromResult<IReadOnlyList<IAssetInfo>>(new List<IAssetInfo>());
+                }).Nested("property").Nested("iv");
+        }
+    }
+}