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Fix JSON schema nullability for readonly properties #132271

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Fix JSON schema nullability for readonly properties #132271

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97def59
Fix JSON schema nullability for readonly properties
Youssef1313 Aug 13, 2026
cb77d27
Update JsonSchemaExporterTests.cs
Youssef1313 Aug 13, 2026
cb11f0e
Make internal
Youssef1313 Aug 13, 2026
a636462
Update JsonSchemaExporterTests.cs
Youssef1313 Aug 14, 2026
658ceeb
Fix nullability
Youssef1313 Aug 18, 2026
7fa91e2
Update JsonSchemaExporterTests.cs
Youssef1313 Aug 18, 2026
3779642
Update JsonSchemaExporterTests.TestTypes.cs
Youssef1313 Aug 18, 2026
e6acbe7
Update JsonSchemaExporterTests.TestTypes.cs
Youssef1313 Aug 18, 2026
a7fc7d2
Update JsonSchemaExporterTests.cs
Youssef1313 Aug 18, 2026
c9f7159
Typo
Youssef1313 Aug 18, 2026
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3 changes: 2 additions & 1 deletion src/libraries/System.Text.Json/src/System/Text/Json/Schema/JsonSchemaExporter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -447,7 +447,8 @@ bool IsNullableSchema(JsonSchemaExporterOptions options)

if (propertyInfo is not null)
{
return propertyInfo.IsGetNullable || propertyInfo.IsSetNullable;
return (propertyInfo.Get is not null && propertyInfo.IsGetNullable) ||

@Youssef1313 Youssef1313 Aug 14, 2026

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@eiriktsarpalis I'm thinking more. Is this whole idea even correct? A property isn't necessarily writeable only via a setter. It could be writeable via a constructor.

public class C
{
    public C(string? s) => S = s ?? string.Empty;

    // get-only property. Non-nullable.
    // But a null is okay to get deserialized.
    // It's not produced by serialization, though.
    public string S { get; }
}

@Youssef1313 Youssef1313 Aug 18, 2026 •
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I switched to an approach to prefer the nullability from AssociatedParameter.

(propertyInfo.Set is not null && propertyInfo.IsSetNullable);
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}

if (typeInfo.IsNullable)
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36 changes: 36 additions & 0 deletions src/libraries/System.Text.Json/tests/Common/JsonSchemaExporterTests.cs
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Expand Up @@ -82,6 +82,30 @@ public void TreatNullObliviousAsNonNullable_True_MarksReferenceTypesAsNonNullabl
Assert.Equal(expectedType, (string)schema["type"]!);
}

[Fact]
public void GetOnlyProperties_DoNotUseSetterNullabilityInSchema()
{
JsonNode schema = Serializer.DefaultOptions.GetJsonSchemaAsNode(typeof(PocoWithGetOnlyProperties));
const string ExpectedJsonSchema = """
{
"type": ["object", "null"],
"properties": {
"Values": {
"type": "array",
"items": { "type": ["string", "null"] }
},
"SingleValueGetOnly": { "type": "string" },
"NullableGetOnly": { "type": ["string", "null"] },
"SingleValueGetSet": { "type": "string" },
"NonNullableReadonlyField": { "type": "string" },
"NullableReadonlyField": { "type": ["string", "null"] }
}
}
""";

AssertValidJsonSchema(typeof(PocoWithGetOnlyProperties), ExpectedJsonSchema, schema);
}

[Theory]
[InlineData(typeof(Type))]
[InlineData(typeof(MethodInfo))]
Expand Down Expand Up @@ -262,6 +286,18 @@ public void LegacySchemaExporter_CanAccessReflectedMembers()

record PocoWithProperty(int Value);

public sealed class PocoWithGetOnlyProperties
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{
public IEnumerable<string> Values => [];
public string SingleValueGetOnly { get; } = "value";
public string? NullableGetOnly { get; }
public string SingleValueGetSet { get; set; } = "value";
[JsonInclude]
public readonly string NonNullableReadonlyField = "value";
[JsonInclude]
public readonly string? NullableReadonlyField;
}

[JsonSerializable(typeof(PocoWithProperty))]
partial class PocoWithPropertyContext : JsonSerializerContext;

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