From 89622d6b669213481803e66e767e8ad30bd1a9a0 Mon Sep 17 00:00:00 2001
From: Kanna Kim <kimkanna18@gmail.com>
Date: Sun, 12 Jul 2026 10:43:55 -0500
Subject: [PATCH] [typescript-fetch] Fix Omit generic using baseName for
 readOnly fields in API requests (#19572)

---
 .../resources/typescript-fetch/apis.mustache  |  2 +-
 .../TypeScriptFetchClientCodegenTest.java     | 14 +++++++
 .../3_0/typescript-fetch/issue_19572.yaml     | 38 +++++++++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 modules/openapi-generator/src/test/resources/3_0/typescript-fetch/issue_19572.yaml

diff --git a/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache b/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
index c045f6241e25..9abbf2590231 100644
--- a/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
@@ -25,7 +25,7 @@ import {
 {{#allParams.0}}
 export interface {{#prefixParameterInterfaces}}{{classname}}{{/prefixParameterInterfaces}}{{operationIdCamelCase}}Request {
 {{#allParams}}
-    {{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{#hasReadOnly}}Omit<{{{dataType}}}, {{#readOnlyVars}}'{{baseName}}'{{^-last}}|{{/-last}}{{/readOnlyVars}}>{{/hasReadOnly}}{{^hasReadOnly}}{{{dataType}}}{{/hasReadOnly}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}};
+    {{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{#hasReadOnly}}Omit<{{{dataType}}}, {{#readOnlyVars}}'{{name}}'{{^-last}}|{{/-last}}{{/readOnlyVars}}>{{/hasReadOnly}}{{^hasReadOnly}}{{{dataType}}}{{/hasReadOnly}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}};
 {{/allParams}}
 }
 
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/fetch/TypeScriptFetchClientCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/fetch/TypeScriptFetchClientCodegenTest.java
index a32753a89c20..5b3b81cdf257 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/fetch/TypeScriptFetchClientCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/typescript/fetch/TypeScriptFetchClientCodegenTest.java
@@ -680,6 +680,20 @@ public void testIssue23380_OmitUsesCorrectPropertyName() throws Exception {
         TestUtils.assertFileContains(modelPath, "export function MissionToJSONTyped(value?: Omit<Mission, 'id'|'taskName'|'singleCar'> | null, ignoreDiscriminator: boolean = false): any {");
     }
 
+    @Test(description = "Verify Omit uses the camelCase property name instead of the baseName for readOnly fields in API requests")
+    public void testIssue19572_OmitUsesCorrectPropertyNameInApi() throws Exception {
+        File output = generate(
+                Collections.emptyMap(),
+                "src/test/resources/3_0/typescript-fetch/issue_19572.yaml"
+        );
+
+        Path modelPath = Paths.get(output + "/apis/DefaultApi.ts");
+        TestUtils.assertFileExists(modelPath);
+        // Ensure Omit uses camelCase names like 'createdAt' and 'updatedAt' instead of snake_case 'created_at' and 'updated_at'
+        TestUtils.assertFileContains(modelPath, "export interface FinancingOptionCreateRequest {");
+        TestUtils.assertFileContains(modelPath, "    financingOption?: Omit<FinancingOption, 'id'|'createdAt'|'updatedAt'|'foo'|'bar'>;");
+    }
+
     private static File generate(
         Map<String, Object> properties
     ) throws IOException {
diff --git a/modules/openapi-generator/src/test/resources/3_0/typescript-fetch/issue_19572.yaml b/modules/openapi-generator/src/test/resources/3_0/typescript-fetch/issue_19572.yaml
new file mode 100644
index 000000000000..1e06de2d284f
--- /dev/null
+++ b/modules/openapi-generator/src/test/resources/3_0/typescript-fetch/issue_19572.yaml
@@ -0,0 +1,38 @@
+openapi: 3.0.0
+info:
+  title: Test API
+  version: 1.0.0
+paths:
+  /financing-options:
+    post:
+      operationId: financingOptionCreate
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/FinancingOption'
+      responses:
+        '200':
+          description: OK
+components:
+  schemas:
+    FinancingOption:
+      type: object
+      properties:
+        id:
+          type: string
+          readOnly: true
+        created_at:
+          type: string
+          format: date-time
+          readOnly: true
+        updated_at:
+          type: string
+          format: date-time
+          readOnly: true
+        foo:
+          type: string
+          readOnly: true
+        bar:
+          type: string
+          readOnly: true