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Version: 4.1

EntityHelper and Decorated Entities

Updating Entity Values with entity.assign()#

When you want to update entity based on user input, you will usually have just plain string ids of entity relations as user input. Normally you would need to use em.getReference() to create references from each id first, and then use those references to update entity relations:

const jon = new Author('Jon Snow', '');
const book = new Book('Book', jon); = orm.em.getReference<Author>(Author, '');

Same result can be easily achieved with entity.assign():

import { wrap } from '@mikro-orm/core';
title: 'Better Book 1',
author: '',
console.log(book.title); // 'Better Book 1'
console.log(; // instance of Author with id: ''
console.log(; // ''

To use entity.assign() on not managed entities, you need to provide EntityManager instance explicitly:

import { wrap } from '@mikro-orm/core';
const book = new Book();
title: 'Better Book 1',
author: '',
}, { em: orm.em });

By default, entity.assign(data) behaves same way as Object.assign(entity, data), e.g. it does not merge things recursively. To enable deep merging of object properties, use second parameter to enable mergeObjects flag:

import { wrap } from '@mikro-orm/core';
book.meta = { foo: 1, bar: 2 };
wrap(book).assign({ meta: { foo: 3 } }, { mergeObjects: true });
console.log(book.meta); // { foo: 3, bar: 2 }
wrap(book).assign({ meta: { foo: 4 } });
console.log(book.meta); // { foo: 4 }

WrappedEntity and wrap() helper#

IWrappedEntity is an interface that defines public helper methods provided by the ORM:

interface IWrappedEntity<T, PK extends keyof T> {
isInitialized(): boolean;
populated(populated?: boolean): void;
init(populated?: boolean, lockMode?: LockMode): Promise<T>;
toReference(): IdentifiedReference<T, PK>;
toObject(ignoreFields?: string[]): Dictionary;
toJSON(...args: any[]): Dictionary;
assign(data: any, options?: AssignOptions | boolean): T;

There are two ways to access those methods. You can either extend BaseEntity (exported from @mikro-orm/core), that defines those methods, or use the wrap() helper to access WrappedEntity instance, where those methods exist.

Users can choose whether they are fine with polluting the entity interface with those additional methods, or they want to keep the interface clean and use the wrap(entity) helper method instead to access them.

Since v4 wrap(entity) no longer returns the entity, now the WrappedEntity instance is being returned. It contains only public methods (init, assign, isInitialized, ...), if you want to access internal properties like __meta or __em, you need to explicitly ask for the helper via wrap(entity, true).

import { BaseEntity } from '@mikro-orm/core';
export class Book extends BaseEntity<Book, 'id'> { ... }

Then you can work with those methods directly:

book.meta = { foo: 1, bar: 2 };
book.assign({ meta: { foo: 3 } }, { mergeObjects: true });
console.log(book.meta); // { foo: 3, bar: 2 }

Accessing internal prefixed properties#

Previously it was possible to access internal properties like __meta or __em from the wrap() helper. Now to access them, you need to use second parameter of wrap:

export class Author { ... }
console.log(wrap(author, true).__meta);
Last updated on by Renovate Bot