[BUG][C++][Pistache] required field is meaningless in requestBodies

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Similar to https://github.com/OpenAPITools/openapi-generator/issues/5880 , required parameters in request bodies are not added to the validate function.

openapi-generator version

6.2.1

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: Test example
  version: 0.0.1
  
paths:
  /data:
      put:
        tags:
          - Data
        summary: My request
        description: |-
          Allows operator to import data.

        operationId: importData
        requestBody:
          $ref: "#/components/requestBodies/ImportDataDTO"
        responses:
          "201":
            description: |-
              201 Data Imported
            content:
              application/json:
                schema:
                  properties:
                    msg:
                      type: string
components:
  schemas:
    MyDataObj:
      description: Coordinates
      properties:
        x:
          type: number
          format: double
        y:
          type: number
          format: double
        z:
          type: number
          format: double
      required:
        - x
        - y
        - z
  requestBodies:
    ImportDataDTO:
      required: true
      content:
        application/json:
          schema:
            properties:
              name:
                type: string
              dataDTO:
                $ref: "#/components/schemas/MyDataObj"
            required:
              - name
              - dataDTO

Generation Details

openapi-generator-cli generate -i example.yaml -g cpp-pistache-server

This will produce:

bool ImportData_request::validate(std::stringstream& msg, const std::string& pathPrefix) const
{
    bool success = true;
    const std::string _pathPrefix = pathPrefix.empty() ? "ImportData_request" : pathPrefix;

            
    return success;
}

I would expect something along the lines of :

bool ImportData_request::validate(std::stringstream& msg, const std::string& pathPrefix) const
{
    bool success = true;
    const std::string _pathPrefix = pathPrefix.empty() ? "ImportData_request" : pathPrefix;

            
    if (!m_DataDTO.validate()) {
        msg << _pathPrefix << ": DataDTO is invalid;";
        success = false;
    }
    return success;
}

Steps to reproduce

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/5880

Suggest a fix

I'm not familiar with the mustache syntax but modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache should be modified to something like:

diff --git a/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache b/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache
index ad38f52d535..776049e6efc 100644
--- a/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache
+++ b/modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache
@@ -60,7 +60,11 @@ bool {{classname}}::validate(std::stringstream& msg, const std::string& pathPref
         const std::string currentValuePath = _pathPrefix + ".{{nameInCamelCase}}";
         {{> model-validation-body }}
     }
-    {{/hasValidation}}{{/isArray}}{{/vars}}{{/isEnum}}{{#vendorExtensions.x-is-string-enum-container}}{{#anyOf}}{{#-first}}
+    {{/hasValidation}}{{#required}}{{#isModel}}
+    if (!m_{{name}}.validate()) {
+        msg << _pathPrefix << ": {{name}} is invalid;";
+        success = false;
+    }{{/isModel}}{{/required}}{{/isArray}}{{/vars}}{{/isEnum}}{{#vendorExtensions.x-is-string-enum-container}}{{#anyOf}}{{#-first}}
     if (!m_value.validate(msg))
     {
         success = false;

Run the openapi-generator-cli command with the provided YAML and inspect modules/openapi-generator/src/main/resources/cpp-pistache-server/model-source.mustache. Compare the generated ImportData_request::validate function with the expected output. Done means required model fields in the request body are validated and invalid data is reported.