Class-validator: Problem with nested object validation

[bkotrys]

Related to: https://github.com/typestack/class-transformer/issues/226

I use class-transformer with class-validator to validate request body. I would like to validate class with nested object - I need to check whether the given object is correct but don't allow to provide an array of objects

How my implementation looks like:

// Class definition with validation rules
class A {
  @IsDefined()
  @IsString()
  public x: string;
  // ... other properties
}

class B {
  @IsDefined()
  @IsString()
  public type!: string;

  @IsDefined()
  @ValidateNested()
  @Type(() => A)
  public nested!: A;
}

// invalid request object with array (B[]) instead of object (B)
var requestObjB = {
   type: "test type"
   nested: [{ x: "test x" }] 
}

// try to validate request object
validate(plainToClass(B, requestObjB))

Validation failed and I get this error:

 TypeError: newValue_1.push is not a function
    at /Users/bartosz/dev/user-data-api/src/TransformOperationExecutor.ts:67:34
    at Array.forEach (<anonymous>)
    at TransformOperationExecutor.transform (/Users/bartosz/dev/user-data-api/src/TransformOperationExecutor.ts:41:30)
    at _loop_1 (/Users/bartosz/dev/user-data-api/src/TransformOperationExecutor.ts:226:43)
    at TransformOperationExecutor.transform (/Users/bartosz/dev/user-data-api/node_modules/class-transformer/TransformOperationExecutor.js:240:17)
    at _loop_1 (/Users/bartosz/dev/user-data-api/src/TransformOperationExecutor.ts:226:43)
    at TransformOperationExecutor.transform (/Users/bartosz/dev/user-data-api/node_modules/class-transformer/TransformOperationExecutor.js:240:17)

Is it possible to solve this problem or maybe there is better way to handle this kind of validation?

[MichalLytek]

public nested!: A[]; not !: A;

[bkotrys]

@19majkel94 It doesn't satisfied me because I don't want to give a chance to send list of objects for nested property.

The rules are:
👍 object (B),
👎 array of objects (B[])

When someone send an array of object I would like to respond with validation error: nested property is in wrong format

[MichalLytek]

The problem is with class-transformer - you declare an object type, you provide an array and it fails on transform.

[bkotrys]

yeah, you are right. I was hoping that there is other way to handle this problem than to validate the format of the request object before converting it with class-transformer, and then re-validate it with the class-validator

[Wintereise]

@19majkel94 So what's the recommended way forward here (since you're familiar with both xformer and validator)?

Obviously, we can't leave this loophole open :(

[bkotrys]

Any updates here?

@19majkel94 So what's the recommended way forward here (since you're familiar with both xformer and validator)?

[vlapo]

I think the only way how to achieve this is https://github.com/typestack/class-validator#defining-validation-schema-without-decorators but I am not sure in what state is this feature.

[michal]

It's pretty old but... adding IsNotEmptyObject or IsObject will not allow arrays, not perfect because will add different error, considering other solutions this was good enough for me.

  @IsDefined()
  @IsNotEmptyObject() / @IsObject()
  @ValidateNested()
  @Type(() => A)
  public nested!: A;