Skip to content

Fix C# GenericHost oneOf serialization for referenced models #24674

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
madhus1218 wants to merge 2 commits into
base: master
Choose a base branch
from
+87 −0
Open

Fix C# GenericHost oneOf serialization for referenced models #24674

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
f6aa83f
fix(csharp): serialize oneOf referenced models in generichost
madhus1218 Aug 11, 2026
e55db64
fix(csharp): handle generichost oneOf converter edge cases
madhus1218 Aug 11, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
34 changes: 34 additions & 0 deletions .../openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -376,7 +376,41 @@

{{/children}}
{{/discriminator}}
{{^model.discriminator}}
{{#composedSchemas}}
{{#oneOf}}
{{^vendorExtensions.x-duplicated-data-type}}
{{#isPrimitiveType}}
if ({{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}} != null)
{
JsonSerializer.Serialize(writer, {{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}}, jsonSerializerOptions);

@cubic-dev-ai cubic-dev-ai Bot Aug 11, 2026

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

P2: For primitive oneOf members the new code serializes the value as a bare JSON primitive and returns before writer.WriteStartObject() is reached. This path is asymmetric with the referenced-object path it sits next to: the object path preserves the parent's sibling properties via WriteProperties, but the primitive path writes only the bare scalar and drops every sibling property (and never emits an object). For a composed model that mixes a primitive oneOf member with sibling properties (e.g. oneOf: [string, Apple] plus a color sibling), serializing when the primitive is selected silently omits the sibling data, so the output won't round-trip. Consider writing the primitive into the object (or documenting that a primitive oneOf cannot be combined with siblings).

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache, line 386:

<comment>For primitive oneOf members the new code serializes the value as a bare JSON primitive and `return`s before `writer.WriteStartObject()` is reached. This path is asymmetric with the referenced-object path it sits next to: the object path preserves the parent's sibling properties via WriteProperties, but the primitive path writes only the bare scalar and drops every sibling property (and never emits an object). For a composed model that mixes a primitive oneOf member with sibling properties (e.g. `oneOf: [string, Apple]` plus a `color` sibling), serializing when the primitive is selected silently omits the sibling data, so the output won't round-trip. Consider writing the primitive into the object (or documenting that a primitive oneOf cannot be combined with siblings).</comment>

<file context>
@@ -376,7 +376,39 @@
+            {{#isPrimitiveType}}
+            if ({{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}} != null)
+            {
+                JsonSerializer.Serialize(writer, {{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}}, jsonSerializerOptions);
+                return;
+            }
</file context>

return;
}

{{/isPrimitiveType}}
{{/vendorExtensions.x-duplicated-data-type}}
{{/oneOf}}
{{/composedSchemas}}
{{/model.discriminator}}
writer.WriteStartObject();
{{^model.discriminator}}
{{#composedSchemas}}
{{#oneOf}}
{{^vendorExtensions.x-duplicated-data-type}}
{{#isModel}}
{{^isContainer}}
if ({{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}} != null)
{
{{baseType}}JsonConverter {{#lambda.camelcase_sanitize_param}}{{baseType}}JsonConverter{{/lambda.camelcase_sanitize_param}} = new {{baseType}}JsonConverter();
{{#lambda.camelcase_sanitize_param}}{{baseType}}JsonConverter{{/lambda.camelcase_sanitize_param}}.WriteProperties(writer, {{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}}, jsonSerializerOptions);

@cubic-dev-ai cubic-dev-ai Bot Aug 11, 2026

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

P2: The referenced oneOf model's properties are written directly into the parent's already-open JSON object (flattened), followed by the parent's own WriteProperties. If a oneOf child schema shares a JSON property name with a sibling property on the parent (or with the discriminator/additionalProperties), the serialized output will contain duplicate keys for that name. The included Fruit sample avoids this only by luck (child keys kind/count/sweet vs parent key color); a child such as apple defining a color property alongside Fruit's color sibling would produce duplicate "color" entries, and on deserialization the parent's value silently wins because it is written last. Consider guarding against name collisions (e.g. wrapper/discriminator object or a name-overlap check) or at least documenting this flattening limitation.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/csharp/libraries/generichost/JsonConverter.mustache, line 404:

<comment>The referenced oneOf model's properties are written directly into the parent's already-open JSON object (flattened), followed by the parent's own WriteProperties. If a oneOf child schema shares a JSON property name with a sibling property on the parent (or with the discriminator/additionalProperties), the serialized output will contain duplicate keys for that name. The included Fruit sample avoids this only by luck (child keys kind/count/sweet vs parent key color); a child such as `apple` defining a `color` property alongside Fruit's `color` sibling would produce duplicate "color" entries, and on deserialization the parent's value silently wins because it is written last. Consider guarding against name collisions (e.g. wrapper/discriminator object or a name-overlap check) or at least documenting this flattening limitation.</comment>

<file context>
@@ -376,7 +376,39 @@
+            if ({{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}} != null)
+            {
+                {{baseType}}JsonConverter {{#lambda.camelcase_sanitize_param}}{{baseType}}JsonConverter{{/lambda.camelcase_sanitize_param}} = ({{baseType}}JsonConverter) jsonSerializerOptions.Converters.First(c => c.CanConvert({{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}}.GetType()));
+                {{#lambda.camelcase_sanitize_param}}{{baseType}}JsonConverter{{/lambda.camelcase_sanitize_param}}.WriteProperties(writer, {{#lambda.camelcase_sanitize_param}}{{classname}}{{/lambda.camelcase_sanitize_param}}.{{name}}, jsonSerializerOptions);
+            }
+
</file context>

}

{{/isContainer}}
{{/isModel}}
{{/vendorExtensions.x-duplicated-data-type}}
{{/oneOf}}
{{/composedSchemas}}
{{/model.discriminator}}

{{#model.discriminator}}
{{#model.hasDiscriminatorWithNonEmptyMapping}}
Expand Down
36 changes: 36 additions & 0 deletions ...ient/petstore/csharp/generichost/net8/OneOf/src/Org.OpenAPITools.Test/Model/FruitTests.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
using Org.OpenAPITools.Model;
using Org.OpenAPITools.Client;
using System.Reflection;
using System.Text.Json;

namespace Org.OpenAPITools.Test.Model
{
Expand Down Expand Up @@ -61,5 +62,40 @@ public void ColorTest()
{
// TODO unit test for the property 'Color'
}

[Fact]
public void SerializeOneOfReferencedObject()
{
var options = new JsonSerializerOptions();
options.Converters.Add(new AppleJsonConverter());
options.Converters.Add(new BananaJsonConverter());
options.Converters.Add(new FruitJsonConverter());
options.Converters.Add(new OrangeJsonConverter());

Fruit fruit = new Fruit(new Apple("red"));

string json = JsonSerializer.Serialize(fruit, options);

Assert.Equal("{\"kind\":\"red\"}", json);
}

[Fact]
public void SerializeOneOfReferencedObjectWithSiblingProperty()
{
var options = new JsonSerializerOptions();
options.Converters.Add(new AppleJsonConverter());
options.Converters.Add(new BananaJsonConverter());
options.Converters.Add(new FruitJsonConverter());
options.Converters.Add(new OrangeJsonConverter());

Fruit fruit = new Fruit(
new Apple("red"),
new Option<string?>("green")
);

string json = JsonSerializer.Serialize(fruit, options);

Assert.Equal("{\"kind\":\"red\",\"color\":\"green\"}", json);
}
}
}
17 changes: 17 additions & 0 deletions samples/client/petstore/csharp/generichost/net8/OneOf/src/Org.OpenAPITools/Model/Fruit.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -237,6 +237,23 @@ public override Fruit Read(ref Utf8JsonReader utf8JsonReader, Type typeToConvert
public override void Write(Utf8JsonWriter writer, Fruit fruit, JsonSerializerOptions jsonSerializerOptions)
{
writer.WriteStartObject();
if (fruit.Apple != null)
{
AppleJsonConverter appleJsonConverter = new AppleJsonConverter();
appleJsonConverter.WriteProperties(writer, fruit.Apple, jsonSerializerOptions);
}

if (fruit.Banana != null)
{
BananaJsonConverter bananaJsonConverter = new BananaJsonConverter();
bananaJsonConverter.WriteProperties(writer, fruit.Banana, jsonSerializerOptions);
}

if (fruit.Orange != null)
{
OrangeJsonConverter orangeJsonConverter = new OrangeJsonConverter();
orangeJsonConverter.WriteProperties(writer, fruit.Orange, jsonSerializerOptions);
}

WriteProperties(writer, fruit, jsonSerializerOptions);
writer.WriteEndObject();
Expand Down
Loading