diff --git a/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetFolderRepository.cs b/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetFolderRepository.cs
index 632a7d523..52f5f9dfd 100644
--- a/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetFolderRepository.cs
+++ b/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetFolderRepository.cs
@@ -10,6 +10,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using MongoDB.Bson.Serialization;
 using MongoDB.Driver;
 using Squidex.Domain.Apps.Entities.Assets;
 using Squidex.Domain.Apps.Entities.Assets.Repositories;
@@ -21,6 +22,8 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
 {
     public sealed partial class MongoAssetFolderRepository : MongoRepositoryBase<MongoAssetFolderEntity>, IAssetFolderRepository
     {
+        private readonly Lazy<string> idField = new Lazy<string>(GetIdField);
+
         public MongoAssetFolderRepository(IMongoDatabase database)
             : base(database)
         {
@@ -64,7 +67,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
                     await Collection.Find(x => x.IndexedAppId == appId && !x.IsDeleted && x.ParentId == parentId).Only(x => x.Id)
                         .ToListAsync();
 
-                return assetFolderEntities.Select(x => Guid.Parse(x["_id"].AsString)).ToList();
+                return assetFolderEntities.Select(x => Guid.Parse(x[idField.Value].AsString)).ToList();
             }
         }
 
@@ -84,5 +87,10 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
                 return assetFolderEntity;
             }
         }
+
+        private static string GetIdField()
+        {
+            return BsonClassMap.LookupClassMap(typeof(MongoAssetFolderEntity)).GetMemberMap(nameof(MongoAssetFolderEntity.Id)).ElementName;
+        }
     }
 }
diff --git a/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetRepository.cs b/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetRepository.cs
index 82578a00c..0815d928b 100644
--- a/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetRepository.cs
+++ b/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Assets/MongoAssetRepository.cs
@@ -10,6 +10,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using MongoDB.Bson.Serialization;
 using MongoDB.Driver;
 using Squidex.Domain.Apps.Entities.Assets;
 using Squidex.Domain.Apps.Entities.Assets.Repositories;
@@ -24,6 +25,8 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
 {
     public sealed partial class MongoAssetRepository : MongoRepositoryBase<MongoAssetEntity>, IAssetRepository
     {
+        private readonly Lazy<string> idField = new Lazy<string>(GetIdField);
+
         public MongoAssetRepository(IMongoDatabase database)
             : base(database)
         {
@@ -100,7 +103,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
                     await Collection.Find(BuildFilter(appId, ids)).Only(x => x.Id)
                         .ToListAsync();
 
-                return assetEntities.Select(x => Guid.Parse(x["_id"].AsString)).ToList();
+                return assetEntities.Select(x => Guid.Parse(x[idField.Value].AsString)).ToList();
             }
         }
 
@@ -112,7 +115,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
                     await Collection.Find(x => x.IndexedAppId == appId && !x.IsDeleted && x.ParentId == parentId).Only(x => x.Id)
                         .ToListAsync();
 
-                return assetEntities.Select(x => Guid.Parse(x["_id"].AsString)).ToList();
+                return assetEntities.Select(x => Guid.Parse(x[idField.Value].AsString)).ToList();
             }
         }
 
@@ -171,5 +174,10 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Assets
                 Filter.In(x => x.Id, ids),
                 Filter.Ne(x => x.IsDeleted, true));
         }
+
+        private static string GetIdField()
+        {
+            return BsonClassMap.LookupClassMap(typeof(MongoAssetEntity)).GetMemberMap(nameof(MongoAssetEntity.Id)).ElementName;
+        }
     }
 }
diff --git a/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Contents/Operations/QueryIdsAsync.cs b/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Contents/Operations/QueryIdsAsync.cs
index 0d7800d3a..b751525ea 100644
--- a/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Contents/Operations/QueryIdsAsync.cs
+++ b/backend/src/Squidex.Domain.Apps.Entities.MongoDb/Contents/Operations/QueryIdsAsync.cs
@@ -10,6 +10,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using MongoDB.Bson.Serialization;
 using MongoDB.Driver;
 using Squidex.Infrastructure.MongoDb;
 using Squidex.Infrastructure.MongoDb.Queries;
@@ -19,6 +20,8 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Operations
 {
     internal sealed class QueryIdsAsync : OperationBase
     {
+        private readonly Lazy<string> idField = new Lazy<string>(GetIdField);
+        private readonly Lazy<string> schemaIdField = new Lazy<string>(GetSchemaIdField);
         private static readonly List<(Guid SchemaId, Guid Id)> EmptyIds = new List<(Guid SchemaId, Guid Id)>();
         private readonly IAppProvider appProvider;
 
@@ -49,7 +52,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Operations
                 await Collection.Find(filter).Only(x => x.Id, x => x.IndexedSchemaId)
                     .ToListAsync();
 
-            return contentEntities.Select(x => (Guid.Parse(x["_si"].AsString), Guid.Parse(x["_id"].AsString))).ToList();
+            return contentEntities.Select(x => (Guid.Parse(x[schemaIdField.Value].AsString), Guid.Parse(x[idField.Value].AsString))).ToList();
         }
 
         public async Task<IReadOnlyList<(Guid SchemaId, Guid Id)>> DoAsync(Guid appId, Guid schemaId, FilterNode<ClrValue> filterNode)
@@ -67,7 +70,7 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Operations
                 await Collection.Find(filter).Only(x => x.Id, x => x.IndexedSchemaId)
                     .ToListAsync();
 
-            return contentEntities.Select(x => (Guid.Parse(x["_si"].AsString), Guid.Parse(x["_id"].AsString))).ToList();
+            return contentEntities.Select(x => (Guid.Parse(x[schemaIdField.Value].AsString), Guid.Parse(x[idField.Value].AsString))).ToList();
         }
 
         public static FilterDefinition<MongoContentEntity> BuildFilter(FilterNode<ClrValue>? filterNode, Guid schemaId)
@@ -85,5 +88,15 @@ namespace Squidex.Domain.Apps.Entities.MongoDb.Contents.Operations
 
             return Filter.And(filters);
         }
+
+        private static string GetIdField()
+        {
+            return BsonClassMap.LookupClassMap(typeof(MongoContentEntity)).GetMemberMap(nameof(MongoContentEntity.Id)).ElementName;
+        }
+
+        private static string GetSchemaIdField()
+        {
+            return BsonClassMap.LookupClassMap(typeof(MongoContentEntity)).GetMemberMap(nameof(MongoContentEntity.Id)).ElementName;
+        }
     }
 }
\ No newline at end of file
diff --git a/backend/src/Squidex.Infrastructure.MongoDb/MongoDb/MongoExtensions.cs b/backend/src/Squidex.Infrastructure.MongoDb/MongoDb/MongoExtensions.cs
index d00c7b140..681dc1884 100644
--- a/backend/src/Squidex.Infrastructure.MongoDb/MongoDb/MongoExtensions.cs
+++ b/backend/src/Squidex.Infrastructure.MongoDb/MongoDb/MongoExtensions.cs
@@ -11,6 +11,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using System.Threading.Tasks.Dataflow;
 using MongoDB.Bson;
+using MongoDB.Bson.Serialization;
 using MongoDB.Driver;
 using Squidex.Infrastructure.States;
 
@@ -77,14 +78,6 @@ namespace Squidex.Infrastructure.MongoDb
             return find.Project<BsonDocument>(Builders<TDocument>.Projection.Include(include1).Include(include2));
         }
 
-        public static IFindFluent<TDocument, BsonDocument> Only<TDocument>(this IFindFluent<TDocument, TDocument> find,
-            Expression<Func<TDocument, object>> include1,
-            Expression<Func<TDocument, object>> include2,
-            Expression<Func<TDocument, object>> include3)
-        {
-            return find.Project<BsonDocument>(Builders<TDocument>.Projection.Include(include1).Include(include2).Include(include3));
-        }
-
         public static IFindFluent<TDocument, TDocument> Not<TDocument>(this IFindFluent<TDocument, TDocument> find,
             Expression<Func<TDocument, object>> exclude)
         {
@@ -98,14 +91,6 @@ namespace Squidex.Infrastructure.MongoDb
             return find.Project<TDocument>(Builders<TDocument>.Projection.Exclude(exclude1).Exclude(exclude2));
         }
 
-        public static IFindFluent<TDocument, TDocument> Not<TDocument>(this IFindFluent<TDocument, TDocument> find,
-            Expression<Func<TDocument, object>> exclude1,
-            Expression<Func<TDocument, object>> exclude2,
-            Expression<Func<TDocument, object>> exclude3)
-        {
-            return find.Project<TDocument>(Builders<TDocument>.Projection.Exclude(exclude1).Exclude(exclude2).Exclude(exclude3));
-        }
-
         public static async Task UpsertVersionedAsync<T, TKey>(this IMongoCollection<T> collection, TKey key, long oldVersion, long newVersion, Func<UpdateDefinition<T>, UpdateDefinition<T>> updater) where T : IVersionedEntity<TKey> where TKey : notnull
         {
             try
@@ -131,7 +116,9 @@ namespace Squidex.Infrastructure.MongoDb
 
                     if (existingVersion != null)
                     {
-                        throw new InconsistentStateException(existingVersion[nameof(IVersionedEntity<TKey>.Version)].AsInt64, oldVersion, ex);
+                        var versionField = BsonClassMap.LookupClassMap(typeof(T)).GetMemberMap(nameof(IVersionedEntity<TKey>.Version)).ElementName;
+
+                        throw new InconsistentStateException(existingVersion[versionField].AsInt64, oldVersion, ex);
                     }
                 }
                 else