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TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Supports MongoDB, MySQL, PostgreSQL and SQLite databases as well as usage with vanilla JavaScript.
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Markdown
---
title: Frequently Asked Questions
---
### How can I synchronize my database schema with the entities?
There are two ways:
- [Schema Generator](schema-generator.md)
- [Migrations](./migrations.md)
```sh
npx mikro-orm schema:update --run
```
### I cannot run the CLI
Make sure you install `@mikro-orm/cli` package locally. If you want to have global installation, you will need to install driver packages globally too.
### EntityManager does not have `createQueryBuilder()` method
The method is there, the issue is in the TS type.
In v4 the `core` package, where `EntityManager` and `EntityRepository` are defined, is not dependent on knex, and therefore it cannot have a method returning a `QueryBuilder`. You need to import the SQL flavour of the EM from the driver package to access the `createQueryBuilder()` method.
> The SQL flavour of EM is actually called `SqlEntityManager`, it is exported both under this name and under `EntityManager` alias, so you can just change the location from where you import.
```typescript
import { EntityManager } from '@mikro-orm/mysql'; // or any other SQL driver package
const em: EntityManager;
const qb = await em.createQueryBuilder(...);
```
Same applies for the `aggregate()` method in mongo driver:
```typescript
import { EntityManager } from '@mikro-orm/mongodb';
const em: EntityManager;
const ret = await em.aggregate(...);
```
> The mongo flavour of EM is actually called `MongoEntityManager`, it is exported both under this name and under `EntityManager` alias, so you can just change the location from where you import.
### How can I add columns to pivot table (M:N relation)
You should model your M:N relation transparently, via 1:m and m:1 properties. More about this can be found in [Composite Keys section](./composite-keys.md#use-case-3-join-table-with-metadata).
### You cannot call `em.flush()` from inside lifecycle hook handlers
You might see this validation error even if you do not use hooks. If that happens, the reason is usually because you do not have [request context](./identity-map) set up properly, and you are reusing one `EntityManager` instance.
### Column is being created with JSON type while the TS type is `string/Date/number/...`
You are probably using the default `ReflectMetadataProvider`, which does not support inferring property type when there is a property initializer.
```ts
@Property()
foo = 'abc';
```
There are two ways around this:
- Use [TsMorphMetadataProvider](./metadata-providers.md#tsmorphmetadataprovider)
- Specify the type explicitly:
```ts
@Property()
foo: string = 'abc';
```
### How to set foreign key by raw id?
There are several ways:
1. Using references:
```ts
const b = new Book();
b.author = em.getReference(Author, 1);
```
2. Using assign helper:
```ts
const b = new Book();
em.assign(b, { author: 1 });
```
3. Using create helper:
```ts
const b = em.create(Book, { author: 1 });
```
### New entity instances get initialized with all properties set to `undefined`
When creating new entity instances, either with `new Book()` or `em.create(Book, {})`, MikroORM should return:
```ts
Book {}
```
But some users might find that this returns an object with properties that are explicitly set to `undefined`:
```ts
Book {
name: undefined,
author: undefined,
createdAt: undefined
}
```
This can cause unexpected behavior, particularly if you're expecting the database to set a default value for a column.
To fix this, disable the [`useDefineForClassFields`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier) option in your tsconfig:
```json
{
"compilerOptions": {
"useDefineForClassFields": false
}
}
```