# Many-to-one / one-to-many relations

Many-to-one / one-to-many is a relation where A contains multiple instances of B, but B contains only one instance of A. Let's take for example `User` and `Photo` entities. User can have multiple photos, but each photo is owned by only one single user.

```
import { Entity, PrimaryGeneratedColumn, Column, ManyToOne } from "typeorm"

import { User } from "./User"



@Entity()

export class Photo {

    @PrimaryGeneratedColumn()

    id: number



    @Column()

    url: string



    @ManyToOne(() => User, (user) => user.photos)

    user: User

}
```

```
import { Entity, PrimaryGeneratedColumn, Column, OneToMany } from "typeorm"

import { Photo } from "./Photo"



@Entity()

export class User {

    @PrimaryGeneratedColumn()

    id: number



    @Column()

    name: string



    @OneToMany(() => Photo, (photo) => photo.user)

    photos: Photo[]

}
```

Here we added `@OneToMany` to the `photos` property and specified the target relation type to be `Photo`. You can omit `@JoinColumn` in a `@ManyToOne` / `@OneToMany` relation. `@OneToMany` cannot exist without `@ManyToOne`. If you want to use `@OneToMany`, `@ManyToOne` is required. However, the inverse is not required: If you only care about the `@ManyToOne` relationship, you can define it without having `@OneToMany` on the related entity. Where you set `@ManyToOne` - its related entity will have "relation id" and foreign key.

This example will produce following tables:

```
+-------------+--------------+----------------------------+

|                         photo                           |

+-------------+--------------+----------------------------+

| id          | int          | PRIMARY KEY AUTO_INCREMENT |

| url         | varchar(255) |                            |

| userId      | int          | FOREIGN KEY                |

+-------------+--------------+----------------------------+



+-------------+--------------+----------------------------+

|                          user                           |

+-------------+--------------+----------------------------+

| id          | int          | PRIMARY KEY AUTO_INCREMENT |

| name        | varchar(255) |                            |

+-------------+--------------+----------------------------+
```

Example how to save such relation:

```
const photo1 = new Photo()

photo1.url = "me.jpg"

await dataSource.manager.save(photo1)



const photo2 = new Photo()

photo2.url = "me-and-bears.jpg"

await dataSource.manager.save(photo2)



const user = new User()

user.name = "John"

user.photos = [photo1, photo2]

await dataSource.manager.save(user)
```

or alternatively you can do:

```
const user = new User()

user.name = "Leo"

await dataSource.manager.save(user)



const photo1 = new Photo()

photo1.url = "me.jpg"

photo1.user = user

await dataSource.manager.save(photo1)



const photo2 = new Photo()

photo2.url = "me-and-bears.jpg"

photo2.user = user

await dataSource.manager.save(photo2)
```

With [cascades](https://typeorm.io/docs/relations/relations.md#cascades) enabled you can save this relation with only one `save` call.

To load a user with photos inside you must specify the relation in `FindOptions`:

```
const userRepository = dataSource.getRepository(User)

const users = await userRepository.find({

    relations: {

        photos: true,

    },

})



// or from inverse side



const photoRepository = dataSource.getRepository(Photo)

const photos = await photoRepository.find({

    relations: {

        user: true,

    },

})
```

Or using `QueryBuilder` you can join them:

```
const users = await dataSource

    .getRepository(User)

    .createQueryBuilder("user")

    .leftJoinAndSelect("user.photos", "photo")

    .getMany()



// or from inverse side



const photos = await dataSource

    .getRepository(Photo)

    .createQueryBuilder("photo")

    .leftJoinAndSelect("photo.user", "user")

    .getMany()
```

With eager loading enabled on a relation, you don't have to specify relations in the find command as it will ALWAYS be loaded automatically. If you use QueryBuilder eager relations are disabled, you have to use `leftJoinAndSelect` to load the relation.