Class-Validator: Array of Objects Validation Example

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Mon, 01/16/2023 - 10:20

Here is a quick snippet for validating an array of objects

import { Type } from 'class-transformer';
import {
		ArrayMinSize,
		IsArray,
		IsObject, ValidateNested
} from 'class-validator';

class ListItem {
		@IsString()
		name: string;
}

class List {
		@IsArray()
		@IsObject({ each: true })
		@ValidateNested({message: ' must be an object with a required property "name" (string)'})
		@Type(() => ListItem)
		items: ListItem[]
}

Validation Errors

So the caller gets the following errors

Invalid Item Type, Array

Payload has an item of type array, instead of object.

{ 
	items: [
		[]
	]
}

Result

[
	"each value in items must be an object"
]

Note: The IsObject validator is triggering the error here.

Invalid Item Type, String

Payload has a item of type string, instead of object.

		{
		items: [
		 ""
		]
}

Result

 [
	"must be an object with a required property "name" (string"
]

Note: The ValidateNested validator is triggering the error here.

Missing Item Property

Payload with one item without a name

{ 
	items: [
	  {}
	]
}

Result

 [
		"items.0.name must be a string",
    "items.0.name should not be empty"
]
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