#3979: Allow to set custom "default value" for extra properties.

docs/en/Object-Extensions.md

@@ -174,6 +174,44 @@ ObjectExtensionManager.Instance
 
 The following sections explain the fundamental property configuration options.
 
+#### Default Value
+
+A default value is automatically set for the new property, which is the natural default value for the property type, like `null` for `string`, `false` for `bool` or `0` for `int`.
+
+There are two ways to override the default value:
+
+##### DefaultValue Option
+
+`DefaultValue` option can be set to any value:
+
+````csharp
+ObjectExtensionManager.Instance
+    .AddOrUpdateProperty<IdentityUser, int>(
+        "MyIntProperty",
+        options =>
+        {
+            options.DefaultValue = 42;
+        });
+````
+
+##### DefaultValueFactory Options
+
+`DefaultValueFactory` can be set to a function that returns the default value:
+
+````csharp
+ObjectExtensionManager.Instance
+    .AddOrUpdateProperty<IdentityUser, int>(
+        "MyIntProperty",
+        options =>
+        {
+            options.DefaultValueFactory = () => 42;
+        });
+````
+
+`options.DefaultValueFactory` has a higher priority than the `options.DefaultValue` .
+
+> Tip: Use `DefaultValueFactory` option only if the default value may change over the time. If it is a constant value, then use the `DefaultValue` option.
+
 #### CheckPairDefinitionOnMapping
 
 Controls how to check property definitions while mapping two extensible objects. See the "Object to Object Mapping" section to understand the `CheckPairDefinitionOnMapping` option better.

framework/src/Volo.Abp.AspNetCore.Mvc.Contracts/Volo/Abp/AspNetCore/Mvc/ApplicationConfigurations/ObjectExtending/ExtensionPropertyDto.cs

@@ -21,5 +21,7 @@ namespace Volo.Abp.AspNetCore.Mvc.ApplicationConfigurations.ObjectExtending
         public List<ExtensionPropertyAttributeDto> Attributes { get; set; }
 
         public Dictionary<string, object> Configuration { get; set; }
+        
+        public object DefaultValue { get; set; }
     }
 }

framework/src/Volo.Abp.AspNetCore.Mvc/Volo/Abp/AspNetCore/Mvc/ApplicationConfigurations/ObjectExtending/CachedObjectExtensionsDtoService.cs

@@ -108,6 +108,7 @@ namespace Volo.Abp.AspNetCore.Mvc.ApplicationConfigurations.ObjectExtending
                 Attributes = new List<ExtensionPropertyAttributeDto>(),
                 DisplayName = CreateDisplayNameDto(propertyConfig),
                 Configuration = new Dictionary<string, object>(),
+                DefaultValue = propertyConfig.GetDefaultValue(),
                 Api = new ExtensionPropertyApiDto
                 {
                     OnGet = new ExtensionPropertyApiGetDto

framework/src/Volo.Abp.ObjectExtending/Volo/Abp/Data/HasExtraPropertiesExtensions.cs

@@ -65,8 +65,13 @@ namespace Volo.Abp.Data
         public static TSource SetDefaultsForExtraProperties<TSource>(this TSource source, Type objectType = null)
             where TSource : IHasExtraProperties
         {
+            if (objectType == null)
+            {
+                objectType = typeof(TSource);
+            }
+
             var properties = ObjectExtensionManager.Instance
-                .GetProperties(objectType ?? typeof(TSource));
+                .GetProperties(objectType);
 
             foreach (var property in properties)
             {
@@ -75,7 +80,7 @@ namespace Volo.Abp.Data
                     continue;
                 }
 
-                source.ExtraProperties[property.Name] = TypeHelper.GetDefaultValue(property.Type);
+                source.ExtraProperties[property.Name] = property.GetDefaultValue();
             }
 
             return source;

framework/src/Volo.Abp.ObjectExtending/Volo/Abp/ObjectExtending/ExtensionPropertyHelper.cs

@@ -5,7 +5,7 @@ using Volo.Abp.Reflection;
 
 namespace Volo.Abp.ObjectExtending
 {
-    public static class ExtensionPropertyHelper
+    internal static class ExtensionPropertyHelper
     {
         public static IEnumerable<Attribute> GetDefaultAttributes(Type type)
         {
@@ -19,5 +19,19 @@ namespace Volo.Abp.ObjectExtending
                 yield return new EnumDataTypeAttribute(type);
             }
         }
+
+        public static object GetDefaultValue(
+            Type propertyType,
+            Func<object> defaultValueFactory, 
+            object defaultValue)
+        {
+            if (defaultValueFactory != null)
+            {
+                return defaultValueFactory();
+            }
+
+            return defaultValue ??
+                   TypeHelper.GetDefaultValue(propertyType);
+        }
     }
 }

framework/src/Volo.Abp.ObjectExtending/Volo/Abp/ObjectExtending/Modularity/ExtensionPropertyConfiguration.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using JetBrains.Annotations;
 using Volo.Abp.Localization;
+using Volo.Abp.Reflection;
 
 namespace Volo.Abp.ObjectExtending.Modularity
 {
@@ -45,6 +46,19 @@ namespace Volo.Abp.ObjectExtending.Modularity
         [NotNull]
         public ExtensionPropertyApiConfiguration Api { get; }
 
+        /// <summary>
+        /// Uses as the default value if <see cref="DefaultValueFactory"/> was not set.
+        /// </summary>
+        [CanBeNull]
+        public object DefaultValue { get; set; }
+
+        /// <summary>
+        /// Used with the first priority to create the default value for the property.
+        /// Uses to the <see cref="DefaultValue"/> if this was not set.
+        /// </summary>
+        [CanBeNull]
+        public Func<object> DefaultValueFactory { get; set; }
+
         public ExtensionPropertyConfiguration(
             [NotNull] EntityExtensionConfiguration entityExtensionConfiguration,
             [NotNull] Type type,
@@ -63,6 +77,12 @@ namespace Volo.Abp.ObjectExtending.Modularity
             Api = new ExtensionPropertyApiConfiguration();
 
             Attributes.AddRange(ExtensionPropertyHelper.GetDefaultAttributes(Type));
+            DefaultValue = TypeHelper.GetDefaultValue(Type);
+        }
+
+        public object GetDefaultValue()
+        {
+            return ExtensionPropertyHelper.GetDefaultValue(Type, DefaultValueFactory, DefaultValue);
         }
     }
 }

framework/src/Volo.Abp.ObjectExtending/Volo/Abp/ObjectExtending/Modularity/ModuleExtensionConfigurationHelper.cs

@@ -152,6 +152,8 @@ namespace Volo.Abp.ObjectExtending.Modularity
                         property.Attributes.AddRange(propertyConfig.Attributes);
                         property.DisplayName = propertyConfig.DisplayName;
                         property.Validators.AddRange(propertyConfig.Validators);
+                        property.DefaultValue = propertyConfig.DefaultValue;
+                        property.DefaultValueFactory = propertyConfig.DefaultValueFactory;
                     }
                 );
         }

framework/src/Volo.Abp.ObjectExtending/Volo/Abp/ObjectExtending/ObjectExtensionPropertyInfo.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using JetBrains.Annotations;
 using Volo.Abp.Localization;
+using Volo.Abp.Reflection;
 
 namespace Volo.Abp.ObjectExtending
 {
@@ -47,6 +48,19 @@ namespace Volo.Abp.ObjectExtending
         [NotNull]
         public Dictionary<object, object> Configuration { get; }
 
+        /// <summary>
+        /// Uses as the default value if <see cref="DefaultValueFactory"/> was not set.
+        /// </summary>
+        [CanBeNull]
+        public object DefaultValue { get; set; }
+
+        /// <summary>
+        /// Used with the first priority to create the default value for the property.
+        /// Uses to the <see cref="DefaultValue"/> if this was not set.
+        /// </summary>
+        [CanBeNull]
+        public Func<object> DefaultValueFactory { get; set; }
+
         public ObjectExtensionPropertyInfo(
             [NotNull] ObjectExtensionInfo objectExtension,
             [NotNull] Type type,
@@ -62,6 +76,12 @@ namespace Volo.Abp.ObjectExtending
             Validators = new List<Action<ObjectExtensionPropertyValidationContext>>();
 
             Attributes.AddRange(ExtensionPropertyHelper.GetDefaultAttributes(Type));
+            DefaultValue = TypeHelper.GetDefaultValue(Type);
+        }
+
+        public object GetDefaultValue()
+        {
+            return ExtensionPropertyHelper.GetDefaultValue(Type, DefaultValueFactory, DefaultValue);
         }
     }
 }

framework/test/Volo.Abp.ObjectExtending.Tests/Volo/Abp/ObjectExtending/ObjectExtensionManager_Tests.cs

@@ -119,6 +119,56 @@ namespace Volo.Abp.ObjectExtending
                 .ShouldNotContain(x => x is RequiredAttribute);
         }
 
+        [Fact]
+        public void Should_Set_DefaultValues()
+        {
+            _objectExtensionManager
+                .AddOrUpdateProperty<MyExtensibleObject, int>("IntProp")
+                .AddOrUpdateProperty<MyExtensibleObject, int>("IntPropWithCustomDefaultValue", property =>
+                {
+                    property.DefaultValue = 42;
+                })
+                .AddOrUpdateProperty<MyExtensibleObject, bool>("BoolProp")
+                .AddOrUpdateProperty<MyExtensibleObject, int?>("NullableIntProp")
+                .AddOrUpdateProperty<MyExtensibleObject, int?>("NullableIntPropWithCustomDefaultValueFactory", property =>
+                {
+                    property.DefaultValueFactory = () => 2;
+                })
+                .AddOrUpdateProperty<MyExtensibleObject, string>("StringProp")
+                .AddOrUpdateProperty<MyExtensibleObject, string>("StringPropWithCustomDefaultValue", property =>
+                {
+                    property.DefaultValue = "custom-value";
+                });
+
+            _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("IntProp")
+                .DefaultValue.ShouldBe(0);
+
+            _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("IntPropWithCustomDefaultValue")
+                .DefaultValue.ShouldBe(42);
+
+            _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("BoolProp")
+                .DefaultValue.ShouldBe(false);
+
+            _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("NullableIntProp")
+                .DefaultValue.ShouldBeNull();
+
+            var propWithDefaultValueFactory = _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("NullableIntPropWithCustomDefaultValueFactory");
+            propWithDefaultValueFactory.GetDefaultValue().ShouldBe(2);
+
+            _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("StringProp")
+                .DefaultValue.ShouldBeNull();
+
+            _objectExtensionManager
+                .GetPropertyOrNull<MyExtensibleObject>("StringPropWithCustomDefaultValue")
+                .DefaultValue.ShouldBe("custom-value");
+        }
+
         private class MyExtensibleObject : ExtensibleObject
         {