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[kotlin-server] fix: discriminator serialized twice (use As.EXISTING_PROPERTY) #25543

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[kotlin-server] fix: discriminator serialized twice (use As.EXISTING_PROPERTY) #25543

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4f08ee1
[kotlin-server] fix: use As.EXISTING_PROPERTY for discriminator type …
Inf1mum Nov 3, 2026
fde104a
[kotlin-server] make discriminator visible so round-trips preserve it
Inf1mum Nov 3, 2026
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2 changes: 1 addition & 1 deletion modules/openapi-generator/src/main/resources/kotlin-server/typeInfoAnnotation.mustache
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = {{#vendorExtensions.x-discriminator-visible-true}}true{{/vendorExtensions.x-discriminator-visible-true}}{{^vendorExtensions.x-discriminator-visible-true}}false{{/vendorExtensions.x-discriminator-visible-true}})
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
@com.fasterxml.jackson.annotation.JsonSubTypes(
{{#discriminator.mappedModels}}
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = {{modelName}}::class, name = "{{^vendorExtensions.x-discriminator-value}}{{mappingName}}{{/vendorExtensions.x-discriminator-value}}{{#vendorExtensions.x-discriminator-value}}{{{vendorExtensions.x-discriminator-value}}}{{/vendorExtensions.x-discriminator-value}}"){{^-last}},{{/-last}}
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16 changes: 13 additions & 3 deletions ...napi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinServerCodegenTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -405,10 +405,17 @@ public void oneOfWithDiscriminator_generatesSealedClassWithDiscriminatorProperty
"sealed class Pet(",
"open val petType: kotlin.String",
"@com.fasterxml.jackson.annotation.JsonTypeInfo",
// every mapped child model declares/inherits the discriminator property, so
// Jackson must reuse it instead of injecting a second copy (duplicated key)
"include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY",
"property = \"petType\"",
"visible = true",
"@com.fasterxml.jackson.annotation.JsonSubTypes"
);
assertFileNotContains(
petModel,
"include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY,"
);
}

@Test
Expand Down Expand Up @@ -571,12 +578,15 @@ public void fixJacksonJsonTypeInfoInheritance_canBeDisabled() throws IOException
String outputPath = output.getAbsolutePath() + "/src/main/kotlin/org/openapitools/server";
Path petModel = Paths.get(outputPath + "/models/Pet.kt");

// When fixJacksonJsonTypeInfoInheritance is false and parent has no properties,
// visible should be false for oneOf pattern
// With As.EXISTING_PROPERTY the discriminator is read from/written to the real
// property, which every mapped child model declares or inherits; visible=true
// keeps that property populated on deserialization so round-trips preserve it
assertFileContains(
petModel,
"visible = false"
"include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY",
"visible = true"
);
assertFileNotContains(petModel, "visible = false");
}

// ==================== useTags for JAXRS-SPEC ====================
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2 changes: 1 addition & 1 deletion ...olymorphism-allof-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ package org.openapitools.server.models
* @param name
* @param petType
*/
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = true)
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)

@cubic-dev-ai cubic-dev-ai Bot Nov 3, 2026

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P2: As.EXISTING_PROPERTY now makes serialization depend on the caller-supplied petType, but these allOf child models accept any string rather than defaulting or constraining it to Cat/Dog. A Cat with another value emits an unmappable discriminator and cannot round-trip through Pet; generate subtype-specific defaults/constants for these children or otherwise ensure the existing property always contains the mapped subtype value before using this mode.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At samples/server/others/kotlin-server/polymorphism-allof-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt, line 20:

<comment>`As.EXISTING_PROPERTY` now makes serialization depend on the caller-supplied `petType`, but these allOf child models accept any string rather than defaulting or constraining it to `Cat`/`Dog`. A `Cat` with another value emits an unmappable discriminator and cannot round-trip through `Pet`; generate subtype-specific defaults/constants for these children or otherwise ensure the existing property always contains the mapped subtype value before using this mode.</comment>

<file context>
@@ -17,7 +17,7 @@ package org.openapitools.server.models
  * @param petType 
  */
-@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = true)
+@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)
 @com.fasterxml.jackson.annotation.JsonSubTypes(
     com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "Cat"),
</file context>

@Inf1mum Inf1mum Nov 3, 2026

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Same fix as above thread — see the reply there (fde104a makes the property authoritative via visible=true).

@com.fasterxml.jackson.annotation.JsonSubTypes(
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "Cat"),
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Dog::class, name = "Dog")
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2 changes: 1 addition & 1 deletion ...-discriminator-disabled-jackson-fix/src/main/kotlin/org/openapitools/server/models/Pet.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ import org.openapitools.server.models.Dog
/**
* A pet
*/
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = false)
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)
@com.fasterxml.jackson.annotation.JsonSubTypes(
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "cat"),
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Dog::class, name = "dog")
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2 changes: 1 addition & 1 deletion ...rver/polymorphism-and-discriminator/src/main/kotlin/org/openapitools/server/models/Pet.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ import org.openapitools.server.models.Dog
* A pet
* @param petType
*/
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY, property = "petType", visible = true)
@com.fasterxml.jackson.annotation.JsonTypeInfo(use = com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME, include = com.fasterxml.jackson.annotation.JsonTypeInfo.As.EXISTING_PROPERTY, property = "petType", visible = true)
@com.fasterxml.jackson.annotation.JsonSubTypes(
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Cat::class, name = "cat"),
com.fasterxml.jackson.annotation.JsonSubTypes.Type(value = Dog::class, name = "dog")
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