Add JsonIgnoreCondition.WhenWritingNull (#39388)

* Add JsonIgnoreCondition.WhenWritingNull * Address review feedback
dotnet · Jul 16, 2020 · 9b3cbc4 · 9b3cbc4
1 parent 950ef6f
commit 9b3cbc4
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Showing 8 changed files with 250 additions and 23 deletions.
diff --git a/src/libraries/System.Text.Json/ref/System.Text.Json.cs b/src/libraries/System.Text.Json/ref/System.Text.Json.cs
@@ -494,6 +494,7 @@ public enum JsonIgnoreCondition
         Never = 0,
         Always = 1,
         WhenWritingDefault = 2,
+        WhenWritingNull = 3,
     }
     public abstract partial class JsonAttribute : System.Attribute
     {

diff --git a/src/libraries/System.Text.Json/src/Resources/Strings.resx b/src/libraries/System.Text.Json/src/Resources/Strings.resx
@@ -533,4 +533,7 @@
   <data name="DictionaryKeyTypeNotSupported" xml:space="preserve">
     <value>The type '{0}' is not a supported Dictionary key type.</value>
   </data>
-</root>
+  <data name="IgnoreConditionOnValueTypeInvalid" xml:space="preserve">
+    <value>The ignore condition 'JsonIgnoreCondition.WhenWritingNull' is not valid on value-type member '{0}' on type '{1}'. Consider using 'JsonIgnoreCondition.WhenWritingDefault'.</value>
+  </data>
+</root>
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonIgnoreCondition.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonIgnoreCondition.cs
@@ -5,9 +5,10 @@ namespace System.Text.Json.Serialization
 {
     /// <summary>
     /// When specified on <see cref="JsonSerializerOptions.DefaultIgnoreCondition"/>,
-    /// <see cref="WhenWritingDefault"/> specifies that properties with default values are ignored during serialization.
+    /// determines when properties and fields across the type graph are ignored.
     /// When specified on <see cref="JsonIgnoreAttribute.Condition"/>, controls whether
-    /// a property is ignored during serialization and deserialization.
+    /// a property is ignored during serialization and deserialization. This option
+    /// overrides the setting on <see cref="JsonSerializerOptions.DefaultIgnoreCondition"/>.
     /// </summary>
     public enum JsonIgnoreCondition
     {
@@ -21,7 +22,13 @@ public enum JsonIgnoreCondition
         Always = 1,
         /// <summary>
         /// If the value is the default, the property is ignored during serialization.
+        /// This is applied to both reference and value-type properties and fields.
         /// </summary>
         WhenWritingDefault = 2,
+        /// <summary>
+        /// If the value is <see langword="null"/>, the property is ignored during serialization.
+        /// This is applied only to reference-type properties and fields.
+        /// </summary>
+        WhenWritingNull = 3,
     }
 }
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs
@@ -125,29 +125,47 @@ private void DetermineSerializationCapabilities(JsonIgnoreCondition? ignoreCondi
             }
         }
 
-        private void DetermineIgnoreCondition(JsonIgnoreCondition? ignoreCondition, bool isReferenceType)
+        private void DetermineIgnoreCondition(JsonIgnoreCondition? ignoreCondition, bool defaultValueIsNull)
         {
             if (ignoreCondition != null)
             {
                 Debug.Assert(MemberInfo != null);
                 Debug.Assert(ignoreCondition != JsonIgnoreCondition.Always);
 
-                if (ignoreCondition != JsonIgnoreCondition.Never)
+                if (ignoreCondition == JsonIgnoreCondition.WhenWritingDefault)
                 {
-                    Debug.Assert(ignoreCondition == JsonIgnoreCondition.WhenWritingDefault);
                     IgnoreDefaultValuesOnWrite = true;
                 }
+                else if (ignoreCondition == JsonIgnoreCondition.WhenWritingNull)
+                {
+                    if (defaultValueIsNull)
+                    {
+                        IgnoreDefaultValuesOnWrite = true;
+                    }
+                    else
+                    {
+                        ThrowHelper.ThrowInvalidOperationException_IgnoreConditionOnValueTypeInvalid(this);
+                    }
+                }
             }
 #pragma warning disable CS0618 // IgnoreNullValues is obsolete
             else if (Options.IgnoreNullValues)
             {
                 Debug.Assert(Options.DefaultIgnoreCondition == JsonIgnoreCondition.Never);
-                if (isReferenceType)
+                if (defaultValueIsNull)
                 {
                     IgnoreDefaultValuesOnRead = true;
                     IgnoreDefaultValuesOnWrite = true;
                 }
             }
+            else if (Options.DefaultIgnoreCondition == JsonIgnoreCondition.WhenWritingNull)
+            {
+                Debug.Assert(!Options.IgnoreNullValues);
+                if (defaultValueIsNull)
+                {
+                    IgnoreDefaultValuesOnWrite = true;
+                }
+            }
             else if (Options.DefaultIgnoreCondition == JsonIgnoreCondition.WhenWritingDefault)
             {
                 Debug.Assert(!Options.IgnoreNullValues);
@@ -164,11 +182,11 @@ private void DetermineIgnoreCondition(JsonIgnoreCondition? ignoreCondition, bool
         public abstract bool GetMemberAndWriteJson(object obj, ref WriteStack state, Utf8JsonWriter writer);
         public abstract bool GetMemberAndWriteJsonExtensionData(object obj, ref WriteStack state, Utf8JsonWriter writer);
 
-        public virtual void GetPolicies(JsonIgnoreCondition? ignoreCondition, bool isReferenceType)
+        public virtual void GetPolicies(JsonIgnoreCondition? ignoreCondition, bool defaultValueIsNull)
         {
             DetermineSerializationCapabilities(ignoreCondition);
             DeterminePropertyName();
-            DetermineIgnoreCondition(ignoreCondition, isReferenceType);
+            DetermineIgnoreCondition(ignoreCondition, defaultValueIsNull);
         }
 
         public abstract object? GetValueAsObject(object obj);

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfT.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfT.cs
@@ -89,7 +89,7 @@ public override void Initialize(
                     }
             }
 
-            GetPolicies(ignoreCondition, isReferenceType: default(T) == null);
+            GetPolicies(ignoreCondition, defaultValueIsNull: Converter.CanBeNull);
         }
 
         public override JsonConverter ConverterBase

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs
@@ -220,7 +220,6 @@ public bool IgnoreNullValues
 
                 if (value && _defaultIgnoreCondition != JsonIgnoreCondition.Never)
                 {
-                    Debug.Assert(_defaultIgnoreCondition == JsonIgnoreCondition.WhenWritingDefault);
                     throw new InvalidOperationException(SR.DefaultIgnoreConditionAlreadySpecified);
                 }
 

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs b/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs
@@ -216,6 +216,14 @@ public static void ThrowInvalidOperationException_JsonIncludeOnNonPublicInvalid(
             throw new InvalidOperationException(SR.Format(SR.JsonIncludeOnNonPublicInvalid, memberInfo.Name, parentType));
         }
 
+        [DoesNotReturn]
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static void ThrowInvalidOperationException_IgnoreConditionOnValueTypeInvalid(JsonPropertyInfo jsonPropertyInfo)
+        {
+            MemberInfo memberInfo = jsonPropertyInfo.MemberInfo!;
+            throw new InvalidOperationException(SR.Format(SR.IgnoreConditionOnValueTypeInvalid, memberInfo.Name, memberInfo.DeclaringType));
+        }
+
         [DoesNotReturn]
         [MethodImpl(MethodImplOptions.NoInlining)]
         public static void ThrowNotSupportedException_ObjectWithParameterizedCtorRefMetadataNotHonored(