I’ve created Stack, using AWS CDK, that extends cdk.Stack. In this stack I define lambda function to create product and define api gateway with method LambdaRestApi. Then I add request validator for this api, but I’m trying to get customised error message, if error occurs during body validation, not standard.

I define model of request:

const createProductModel = new apigateway.Model(
      this,
      "CreateProductModel",
      {
        restApi: api,
        contentType: "application/json",
        modelName: "CreateProductModel",
        schema: {
          type: apigateway.JsonSchemaType.OBJECT,
          properties: {
            title: { type: apigateway.JsonSchemaType.STRING, minLength: 1 },
            description: { type: apigateway.JsonSchemaType.STRING },
            price: { type: apigateway.JsonSchemaType.NUMBER, minimum: 0 },
            count: { type: apigateway.JsonSchemaType.NUMBER, minimum: 1 },
          },
          required: ["title", "price", "description", "count"],
        },
      }
    );

Define error template and model for error response

    const errorResponseTemplate = JSON.stringify({
      message: "$context.error.validationErrorString",
    });
    const errorResponseModel = new apigateway.Model(
      this,
      "ErrorResponseModel",
      {
        restApi: api,
        contentType: "application/json",
        modelName: "ErrorResponseModel",
        schema: {
          type: apigateway.JsonSchemaType.OBJECT,
          properties: {
            message: { type: apigateway.JsonSchemaType.STRING },
          },
          required: ["message"],
        },
      }
    );

Define request validator

    const requestValidator = new apigateway.RequestValidator(
      this,
      "CreateProductRequestValidator",
      {
        restApi: api,
        validateRequestBody: true,
        validateRequestParameters: false,
      }
    );

And then I’m trying to pass all these during adding method for resource. I pass errorResponseTemplate in integrationResponses option and I expected, that I get message that contains specified error

   productsResource.addMethod(
      "POST",
      new apigateway.LambdaIntegration(createProductFunction, {
        integrationResponses: [
          {
            selectionPattern: "(n|.)+",
            statusCode: "400",
            responseTemplates: { "application/json": errorResponseTemplate },
          },
        ],
      }),
      {
        requestValidator: requestValidator,
        requestModels: {
          "application/json": createProductModel,
        },
        methodResponses: [
          {
            statusCode: "400",
            responseModels: {
              "application/json": errorResponseModel,
            },
          },
          {
            statusCode: "201",
            responseModels: {
              "application/json": apigateway.Model.EMPTY_MODEL,
            },
          },
        ],
      }
    );

I expected, that I get custom message about error, for example “field price is required”, but I get message “Invalid request body”