---
title: Defining Entities
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';

Entities are simple javascript objects (so called POJO) without restrictions and without the need to extend base classes. Using [entity constructors](./entity-constructors.md) works as well - they are never executed for managed entities (loaded from database). Every entity is required to have a primary key.

Entities can be defined in two ways:

- Decorated classes - the attributes of the entity, as well as each property are provided via decorators. We use `@Entity()` decorator on the class. Entity properties are decorated either with `@Property` decorator, or with one of reference decorators: `@ManyToOne`, `@OneToMany`, `@OneToOne` and `@ManyToMany`. Check out the full [decorator reference](./decorators.md).
- `EntitySchema` helper - With `EntitySchema` helper we define the schema programmatically. We can use regular classes as well as interfaces. This approach also allows to re-use partial entity definitions (e.g. traits/mixins). Read more about this in [Defining Entities via EntitySchema section](./entity-schema.md).

Moreover, how the metadata extraction from decorators happens is controlled via `MetadataProvider`. Two main metadata providers are:

- `ReflectMetadataProvider` - uses `reflect-metadata` to read the property types. Faster but simpler and more verbose.
- `TsMorphMetadataProvider` - uses `ts-morph` to read the type information from the TypeScript compiled API. Heavier (requires full TS as a dependency), but allows DRY entity definition. With `ts-morph` we are able to extract the type as it is defined in the code, including interface names, as well as optionality of properties.

Read more about them in the [Metadata Providers section](./metadata-providers.md).

> Current set of decorators in MikroORM is designed to work with the `tsc`. Using `babel` is also possible, but requires some additional setup. Read more about it [here](./usage-with-babel.md). For notes about `webpack`, read the [deployment section](./deployment.md).
>
> `ts-morph` is compatible only with the `tsc` approach.

> From v3 we can also use default exports when defining your entity.

Example definition of a `Book` entity follows. We can switch the tabs to see the difference for various ways:

<Tabs
  groupId="entity-def"
  defaultValue="reflect-metadata"
  values={[
    {label: 'reflect-metadata', value: 'reflect-metadata'},
    {label: 'ts-morph', value: 'ts-morph'},
    {label: 'EntitySchema', value: 'entity-schema'},
  ]
  }>
  <TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
@Entity()
export class Book extends CustomBaseEntity {

  @Property()
  title!: string;

  @ManyToOne(() => Author)
  author!: Author;

  @ManyToOne(() => Publisher, { ref: true, nullable: true })
  publisher?: Ref<Publisher>;

  @ManyToMany({ entity: 'BookTag', fixedOrder: true })
  tags = new Collection<BookTag>(this);

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
export class Book extends CustomBaseEntity {

  @Property()
  title!: string;

  @ManyToOne()
  author!: Author;

  @ManyToOne()
  publisher?: Ref<Publisher>;

  @ManyToMany({ fixedOrder: true })
  tags = new Collection<BookTag>(this);

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
export interface IBook extends CustomBaseEntity {
  title: string;
  author: Author;
  publisher?: Ref<Publisher>;
  tags: Collection<BookTag>;
}

export const Book = new EntitySchema<IBook, CustomBaseEntity>({
  name: 'Book',
  extends: 'CustomBaseEntity',
  properties: {
    title: { type: 'string' },
    author: { kind: 'm:1', entity: 'Author' },
    publisher: { kind: 'm:1', entity: 'Publisher', ref: true, nullable: true },
    tags: { kind: 'm:n', entity: 'BookTag', fixedOrder: true },
  },
});
```

  </TabItem>
</Tabs>

> Including `{ wrappedEntity: true }` in your `Ref` property definitions will wrap the reference, providing access to helper methods like `.load` and `.unwrap`, which can be helpful for loading data and changing the type of your references where you plan to use them.

Here is another example of `Author` entity, that was referenced from the `Book` one, this time defined for mongo:

<Tabs
  groupId="entity-def"
  defaultValue="reflect-metadata"
  values={[
    {label: 'reflect-metadata', value: 'reflect-metadata'},
    {label: 'ts-morph', value: 'ts-morph'},
    {label: 'EntitySchema', value: 'entity-schema'},
  ]
  }>
  <TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
@Entity()
export class Author {

  @PrimaryKey()
  _id!: ObjectId;

  @SerializedPrimaryKey()
  id!: string;

  @Property()
  createdAt = new Date();

  @Property({ onUpdate: () => new Date() })
  updatedAt = new Date();

  @Property()
  name!: string;

  @Property()
  email!: string;

  @Property({ nullable: true })
  age?: number;

  @Property()
  termsAccepted: boolean = false;

  @Property({ nullable: true })
  identities?: string[];

  @Property({ nullable: true })
  born?: Date;

  @OneToMany(() => Book, book => book.author)
  books = new Collection<Book>(this);

  @ManyToMany(() => Author)
  friends = new Collection<Author>(this);

  @ManyToOne(() => Book, { nullable: true })
  favouriteBook?: Book;

  @Property({ version: true })
  version!: number;

  constructor(name: string, email: string) {
    this.name = name;
    this.email = email;
  }

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
@Entity()
export class Author {

  @PrimaryKey()
  _id!: ObjectId;

  @SerializedPrimaryKey()
  id!: string;

  @Property()
  createdAt = new Date();

  @Property({ onUpdate: () => new Date() })
  updatedAt = new Date();

  @Property()
  name!: string;

  @Property()
  email!: string;

  @Property()
  age?: number;

  @Property()
  termsAccepted = false;

  @Property()
  identities?: string[];

  @Property()
  born?: Date;

  @OneToMany(() => Book, book => book.author)
  books = new Collection<Book>(this);

  @ManyToMany()
  friends = new Collection<Author>(this);

  @ManyToOne()
  favouriteBook?: Book;

  @Property({ version: true })
  version!: number;

  constructor(name: string, email: string) {
    this.name = name;
    this.email = email;
  }

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
export class Author {

  _id!: ObjectId;
  id!: string;
  createdAt = new Date();
  updatedAt = new Date();
  name!: string;
  email!: string;
  age?: number;
  termsAccepted = false;
  identities?: string[];
  born?: Date;
  books = new Collection<Book>(this);
  friends = new Collection<Author>(this);
  favouriteBook?: Book;
  version!: number;

  constructor(name: string, email: string) {
    this.name = name;
    this.email = email;
  }

}

export const AuthorSchema = new EntitySchema<Author>({
  class: Author,
  properties: {
    _id: { type: 'ObjectId', primary: true },
    id: { type: String, serializedPrimaryKey: true },
    createdAt: { type: Date },
    updatedAt: { type: Date, onUpdate: () => new Date() },
    name: { type: String },
    email: { type: String },
    age: { type: Number, nullable: true },
    termsAccepted: { type: Boolean }
    identities: { type: 'string[]', nullable: true }
    born: { type: Date, nullable: true }
    books: { kind: '1:m', entity: () => Book, mappedBy: book => book.author }
    friends: { kind: 'm:n', entity: () => Author }
    favouriteBook: { kind: 'm:1', entity: () => Book, nullable: true };
    version: { type: Number, version: true };
  },
});
```

  </TabItem>
</Tabs>

More information about modelling relationships can be found on [modelling relationships page](./relationships.md).

For an example of Vanilla JavaScript usage, take a look [here](./usage-with-js.md).

## Optional Properties

With the default `reflect-metadata` provider, we need to mark each optional property as `nullable: true`. When using `ts-morph`, if you define the property as optional (marked with `?`), this will be automatically considered as nullable property (mainly for SQL schema generator).

<Tabs
  groupId="entity-def"
  defaultValue="reflect-metadata"
  values={[
    {label: 'reflect-metadata', value: 'reflect-metadata'},
    {label: 'ts-morph', value: 'ts-morph'},
    {label: 'EntitySchema', value: 'entity-schema'},
  ]
  }>
  <TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
@ManyToOne(() => Book, { nullable: true })
favouriteBook?: Book;
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
@ManyToOne()
favouriteBook?: Book;
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
properties: {
  favouriteBook: { kind: 'm:1', entity: () => Book, nullable: true },
},
```

  </TabItem>
</Tabs>

## Default values

We can set default value of a property in 2 ways:

1. Use runtime default value of the property. This approach should be preferred as long as we are not using any native database function like `now()`. With this approach our entities will have the default value set even before it is actually persisted into the database (e.g. when we instantiate new entity via `new Author()` or `em.create(Author, { ... })`.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
@Property()
foo: number & Opt = 1;

@Property()
bar: string & Opt = 'abc';

@Property()
baz: Date & Opt = new Date();
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
@Property()
foo: number & Opt = 1;

@Property()
bar: string & Opt = 'abc';

@Property()
baz: Date & Opt = new Date();
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
properties: {
  foo: { type: Number, onCreate: () => 1 },
  bar: { type: String, onCreate: () => 'abc' },
  baz: { type: Date, onCreate: () => new Date() },
},
```

  </TabItem>
</Tabs>

2. Use `default` parameter of `@Property` decorator. This way the actual default value will be provided by the database, and automatically mapped to the entity property after it is being persisted (after flush). To use SQL functions like `now()`, use `defaultRaw`.

> Since v4 you should use `defaultRaw` for SQL functions, as `default` with string values will be automatically quoted.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
@Property({ default: 1 })
foo!: number & Opt;

@Property({ default: 'abc' })
bar!: string & Opt;

@Property({ defaultRaw: 'now' })
baz!: Date & Opt;
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
@Property({ default: 1 })
foo!: number & Opt;

@Property({ default: 'abc' })
bar!: string & Opt;

@Property({ defaultRaw: 'now' })
baz!: Date & Opt;
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
properties: {
  foo: { type: Number, default: 1 },
  bar: { type: String, default: 'abc' },
  baz: { type: Date, defaultRaw: 'now' },
},
```

  </TabItem>
</Tabs>

Note that we use the `Opt` type to intersect with the property type to tell the ORM (on type level) that the property should be considered optional for input types (e.g. in `em.create()`)), but will be present for managed entities (e.g. `EntityDTO` type).

## Enums

To define an enum property, use `@Enum()` decorator. Enums can be either numeric or string values.

For schema generator to work properly in case of string enums, we need to define the enum in the same file as where it is used, so its values can be automatically discovered. If we want to define the enum in another file, we should re-export it also in place where we use it.

Another possibility is to provide the reference to the enum implementation in the decorator via `@Enum(() => UserRole)`.

> We can also set enum items manually via `items: string[]` attribute.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
import { OutsideEnum } from './OutsideEnum.ts';

@Entity()
export class User {

  @Enum(() => UserRole)
  role!: UserRole; // string enum

  @Enum(() => UserStatus)
  status!: UserStatus; // numeric/const enum

  @Enum(() => OutsideEnum)
  outside!: OutsideEnum; // string enum defined outside of this file

  @Enum({ items: () => OutsideNullableEnum, nullable: true })
  outsideNullable?: OutsideNullableEnum; // string enum defined outside of this file, may be null

}

export enum UserRole {
  ADMIN = 'admin',
  MODERATOR = 'moderator',
  USER = 'user',
}

export const enum UserStatus {
  DISABLED,
  ACTIVE,
}

// or we could reexport OutsideEnum
// export { OutsideEnum } from './OutsideEnum.ts';
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
import { OutsideEnum } from './OutsideEnum.ts';

@Entity()
export class User {

  @Enum(() => UserRole)
  role!: UserRole; // string enum

  @Enum(() => UserStatus)
  status!: UserStatus; // numeric enum

  @Enum(() => OutsideEnum)
  outside!: OutsideEnum; // string enum defined outside of this file

  @Enum({ items: () => OutsideNullableEnum })
  outsideNullable?: OutsideNullableEnum; // string enum defined outside of this file, may be null

}

export enum UserRole {
  ADMIN = 'admin',
  MODERATOR = 'moderator',
  USER = 'user',
}

export const enum UserStatus {
  DISABLED,
  ACTIVE,
}

// or we could reexport OutsideEnum
// export { OutsideEnum } from './OutsideEnum.ts';
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
properties: {
  // string enum
  role: { enum: true, items: () => UserRole },
  // numeric enum
  status: { enum: true, items: () => UserStatus },
  // string enum defined outside of this file
  outside: { enum: true, items: () => OutsideEnum },
  // string enum defined outside of this file, may be null
  outsideNullable: { enum: true, items: () => OutsideNullableEnum, nullable: true },
},
```

  </TabItem>
</Tabs>

### PostgreSQL native enums

By default, the PostgreSQL driver, represents enums as a text columns with check constraints. Since v6, you can opt-in for a native enums by setting the `nativeEnumName` option.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
@Entity()
export class User {

  @Enum({ items: () => UserRole, nativeEnumName: 'user_role' })
  role!: UserRole;

}

export enum UserRole {
  ADMIN = 'admin',
  MODERATOR = 'moderator',
  USER = 'user',
}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
@Entity()
export class User {

  @Enum({ items: () => UserRole, nativeEnumName: 'user_role' })
  role!: UserRole;

}

export enum UserRole {
  ADMIN = 'admin',
  MODERATOR = 'moderator',
  USER = 'user',
}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
export enum UserRole {
  ADMIN = 'admin',
  MODERATOR = 'moderator',
  USER = 'user',
}

properties: {
  role: { enum: true, nativeEnumName: 'user_role', items: () => UserRole },
},
```

  </TabItem>
</Tabs>

## Enum arrays

We can also use array of values for enum, in that case, `EnumArrayType` type will be used automatically, that will validate items on flush.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/User.ts"
enum Role {
  User = 'user',
  Admin = 'admin',
}

@Enum({ items: () => Role, array: true, default: [Role.User] })
roles = [Role.User];
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/User.ts"
enum Role {
  User = 'user',
  Admin = 'admin',
}

@Enum({ default: [Role.User] })
roles = [Role.User];
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/User.ts"
enum Role {
  User = 'user',
  Admin = 'admin',
}

properties: {
  roles: { enum: true, array: true, default: [Role.User], items: () => Role },
},
```

  </TabItem>
</Tabs>

## Mapping directly to primary keys

Sometimes we might want to work only with the primary key of a relation. To do that, we can use `mapToPk` option on M:1 and 1:1 relations:

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/User.ts"
@ManyToOne(() => User, { mapToPk: true })
user: number;
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/User.ts"
@ManyToOne(() => User, { mapToPk: true })
user: number;
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/User.ts"
properties: {
  user: { entity: () => User, mapToPk: true },
},
```

  </TabItem>
</Tabs>

For composite keys, this will give us ordered tuple representing the raw PKs, which is the internal format of composite PK:

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/User.ts"
@ManyToOne(() => User, { mapToPk: true })
user: [string, string]; // [first_name, last_name]
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/User.ts"
@ManyToOne(() => User, { mapToPk: true })
user: [string, string]; // [first_name, last_name]
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/User.ts"
properties: {
  user: { entity: () => User, mapToPk: true },
},
```

  </TabItem>
</Tabs>

## Formulas

`@Formula()` decorator can be used to map some SQL snippet to your entity. The SQL fragment can be as complex as you want and even include subselects.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Box.ts"
@Formula('obj_length * obj_height * obj_width')
objectVolume?: number;
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Box.ts"
@Formula('obj_length * obj_height * obj_width')
objectVolume?: number;
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Box.ts"
properties: {
  objectVolume: { formula: 'obj_length * obj_height * obj_width' },
},
```

  </TabItem>
</Tabs>

Formulas will be added to the select clause automatically. In case you are facing problems with `NonUniqueFieldNameException`, you can define the formula as a callback that will receive the entity alias in the parameter:

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Box.ts"
@Formula(alias => `${alias}.obj_length * ${alias}.obj_height * ${alias}.obj_width`)
objectVolume?: number;
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Box.ts"
@Formula(alias => `${alias}.obj_length * ${alias}.obj_height * ${alias}.obj_width`)
objectVolume?: number;
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Box.ts"
properties: {
  objectVolume: { formula: alias => `${alias}.obj_length * ${alias}.obj_height * ${alias}.obj_width` },
},
```

  </TabItem>
</Tabs>

## Indexes

We can define indexes via `@Index()` decorator, for unique indexes, we can use `@Unique()` decorator. We can use it either on entity class, or on entity property.

To define complex indexes, we can use index expressions. They allow us to specify the final `create index` query and an index name - this name is then used for index diffing, so the schema generator will only try to create it if it's not there yet, or remove it, if it's no longer defined in the entity. Index expressions are not bound to any property, rather to the entity itself (we can still define them on both entity and property level).

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Author.ts"
@Entity()
@Index({ properties: ['name', 'age'] }) // compound index, with generated name
@Index({ name: 'custom_idx_name', properties: ['name'] }) // simple index, with custom name
@Unique({ properties: ['name', 'email'] })
export class Author {

  @Property()
  @Unique()
  email!: string;

  @Property()
  @Index() // generated name
  age?: number;

  @Index({ name: 'born_index' })
  @Property()
  born?: Date;

  @Index({ name: 'custom_index_expr', expression: 'alter table `author` add index `custom_index_expr`(`title`)' })
  @Property()
  title!: string;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Author.ts"
@Entity()
@Index({ properties: ['name', 'age'] }) // compound index, with generated name
@Index({ name: 'custom_idx_name', properties: ['name'] }) // simple index, with custom name
@Unique({ properties: ['name', 'email'] })
export class Author {

  @Property()
  @Unique()
  email!: string;

  @Property()
  @Index() // generated name
  age?: number;

  @Index({ name: 'born_index' })
  @Property()
  born?: Date;

  @Index({ name: 'custom_index_expr', expression: 'alter table `author` add index `custom_index_expr`(`title`)' })
  @Property()
  title!: string;

}

```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Author.ts"
export const AuthorSchema = new EntitySchema<Author, CustomBaseEntity>({
  class: Author,
  indexes: [
    { properties: ['name', 'age'] }, // compound index, with generated name
    { name: 'custom_idx_name', properties: ['name'] }, // simple index, with custom name
    { name: 'custom_index_expr', expression: 'alter table `author` add index `custom_index_expr`(`title`)' },
  ],
  uniques: [
    { properties: ['name', 'email'] },
  ],
  properties: {
    email: { type: 'string', unique: true }, // generated name
    age: { type: 'number', nullable: true, index: true }, // generated name
    born: { type: Date, nullable: true, index: 'born_index' },
    title: { type: 'string' },
  },
});
```

  </TabItem>
</Tabs>

## Check constraints

We can define check constraints via `@Check()` decorator. We can use it either on entity class, or on entity property. It has a required `expression` property, that can be either a string or a callback, that receives map of property names to column names. Note that we need to use the generic type argument if we want TypeScript suggestions for the property names.

> Check constraints are currently supported only in postgres driver.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
@Entity()
// with generated name based on the table name
@Check({ expression: 'price1 >= 0' })
// with explicit name
@Check({ name: 'foo', expression: columns => `${columns.price1} >= 0` })
// with explicit type argument we get autocomplete on `columns`
@Check<FooEntity>({ expression: columns => `${columns.price1} >= 0` })
export class Book {

  @PrimaryKey()
  id!: number;

  @Property()
  price1!: number;

  @Property()
  @Check({ expression: 'price2 >= 0' })
  price2!: number;

  @Property({ check: columns => `${columns.price3} >= 0` })
  price3!: number;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
// with generated name based on the table name
@Check({ expression: 'price1 >= 0' })
// with explicit name
@Check({ name: 'foo', expression: columns => `${columns.price1} >= 0` })
// with explicit type argument we get autocomplete on `columns`
@Check<FooEntity>({ expression: columns => `${columns.price1} >= 0` })
export class Book {

  @PrimaryKey()
  id!: number;

  @Property()
  price1!: number;

  @Property()
  @Check({ expression: 'price2 >= 0' })
  price2!: number;

  @Property({ check: columns => `${columns.price3} >= 0` })
  price3!: number;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
export const BookSchema = new EntitySchema<Book>({
  class: Book,
  checks: [
    { expression: 'price1 >= 0' },
    { name: 'foo', expression: columns => `${columns.price1} >= 0` },
    { expression: columns => `${columns.price1} >= 0` },
    { propertyName: 'price2', expression: 'price2 >= 0' },
    { propertyName: 'price3', expression: columns => `${columns.price3} >= 0` },
  ],
  properties: {
    id: { type: 'number', primary: true },
    price1: { type: 'number' },
    price2: { type: 'number' },
    price3: { type: 'number' },
  },
});
```

  </TabItem>
</Tabs>

## Custom Types

We can define custom types by extending `Type` abstract class. It has 4 optional methods:

- `convertToDatabaseValue(value: any, platform: Platform): any`

  Converts a value from its JS representation to its database representation of this type.

- `convertToJSValue(value: any, platform: Platform): any`

  Converts a value from its database representation to its JS representation of this type.

- `toJSON(value: any, platform: Platform): any`

  Converts a value from its JS representation to its serialized JSON form of this type. By default converts to the database value.

- `getColumnType(prop: EntityProperty, platform: Platform): string`

  Gets the SQL declaration snippet for a field of this type.

More information can be found in [Custom Types](./custom-types.md) section.

## Lazy scalar properties

We can mark any property as `lazy: true` to omit it from the select clause. This can be handy for properties that are too large, and you want to have them available only sometimes, like a full text of an article.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
@Property({ columnType: 'text', lazy: true })
text: string;
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Property({ columnType: 'text', lazy: true })
text: string;
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
properties: {
  text: { columnType: 'text', lazy: true },
}
```

  </TabItem>
</Tabs>

We can use `populate` parameter to load them.

```ts
const b1 = await em.find(Book, 1); // this will omit the `text` property
const b2 = await em.find(Book, 1, { populate: ['text'] }); // this will load the `text` property
```

> If the entity is already loaded and you need to populate a lazy scalar property, you might need to pass `refresh: true` in the `FindOptions`.

### `ScalarReference` wrapper

Similarly to the `Reference` wrapper, we can also wrap lazy scalars with `Ref` into a `ScalarReference` object.

```ts
@Property({ lazy: true, ref: true })
passwordHash!: Ref<string>;
```

The `Ref` type automatically resolves to `ScalarReference` for non-object types. You can use it explicitly if you want to wrap an object scalar property (e.g. JSON value).

```ts
const user = await em.findOne(User, 1);
const passwordHash = await user.passwordHash.load();
```

## Virtual Properties

We can define our properties as virtual, either as a method, or via JavaScript `get/set`.

Following example defines User entity with `firstName` and `lastName` database fields, that are both hidden from the serialized response, replaced with virtual properties `fullName` (defined as a classic method) and `fullName2` (defined as a JavaScript getter).

> For JavaScript getter you need to provide `{ persist: false }` option otherwise the value would be stored in the database.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/User.ts"
@Entity()
export class User {

  [HiddenProps]?: 'firstName' | 'lastName';

  @Property({ hidden: true })
  firstName!: string;

  @Property({ hidden: true })
  lastName!: string;

  @Property({ name: 'fullName' })
  getFullName() {
    return `${this.firstName} ${this.lastName}`;
  }

  @Property({ persist: false })
  get fullName2() {
    return `${this.firstName} ${this.lastName}`;
  }

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/User.ts"
@Entity()
export class User {

  [HiddenProps]?: 'firstName' | 'lastName';

  @Property({ hidden: true })
  firstName!: string;

  @Property({ hidden: true })
  lastName!: string;

  @Property({ name: 'fullName' })
  getFullName() {
    return `${this.firstName} ${this.lastName}`;
  }

  @Property({ persist: false })
  get fullName2() {
    return `${this.firstName} ${this.lastName}`;
  }

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/User.ts"
export class User {

  [HiddenProps]?: 'firstName' | 'lastName';

  firstName!: string;
  lastName!: string;

  getFullName() {
    return `${this.firstName} ${this.lastName}`;
  }

  get fullName2() {
    return `${this.firstName} ${this.lastName}`;
  }
}

properties: {
  firstName: { type: String, hidden: true },
  lastName: { type: String, hidden: true },
  fullName: { type: 'method', persist: false, getter: true, getterName: 'getFullName' },
  fullName2: { type: 'method', persist: false, getter: true },
}
```

  </TabItem>
</Tabs>

```ts
const repo = em.getRepository(User);
const author = repo.create({ firstName: 'Jon', lastName: 'Snow' });

console.log(author.getFullName()); // 'Jon Snow'
console.log(author.fullName2); // 'Jon Snow'
console.log(wrap(author).toJSON()); // { fullName: 'Jon Snow', fullName2: 'Jon Snow' }
```

## Entity file names

Starting with MikroORM 4.2, there is no limitation for entity file names. It is now also possible to define multiple entities in a single file using folder based discovery.

## Using custom base entity

We can define our own base entity with properties that are required on all entities, like primary key and created/updated time. Single table inheritance is also supported.

Read more about this topic in [Inheritance Mapping](./inheritance-mapping.md) section.

> If you are initializing the ORM via `entities` option, you need to specify all your base entities as well.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/CustomBaseEntity.ts"
import { v4 } from 'uuid';

export abstract class CustomBaseEntity {

  @PrimaryKey()
  uuid = v4();

  @Property()
  createdAt = new Date();

  @Property({ onUpdate: () => new Date() })
  updatedAt = new Date();

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/CustomBaseEntity.ts"
import { v4 } from 'uuid';

export abstract class CustomBaseEntity {

  @PrimaryKey()
  uuid = v4();

  @Property()
  createdAt = new Date();

  @Property({ onUpdate: () => new Date() })
  updatedAt = new Date();

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/CustomBaseEntity.ts"
import { v4 } from 'uuid';

export interface CustomBaseEntity {
  uuid: string;
  createdAt: Date;
  updatedAt: Date;
}

export const schema = new EntitySchema<CustomBaseEntity>({
  name: 'CustomBaseEntity',
  abstract: true,
  properties: {
    uuid: { type: 'uuid', onCreate: () => v4(), primary: true },
    createdAt: { type: 'Date', onCreate: () => new Date(), nullable: true },
    updatedAt: { type: 'Date', onCreate: () => new Date(), onUpdate: () => new Date(), nullable: true },
  },
});
```

  </TabItem>
</Tabs>

There is a special case, when we need to annotate the base entity - if we are using folder based discovery, and the base entity is not using any decorators (e.g. it does not define any decorated property). In that case, we need to mark it as abstract:

```ts
@Entity({ abstract: true })
export abstract class CustomBaseEntity {
  // ...
}
```

## SQL Generated columns

To use generated columns, you can either use the `generated` option, or specify it as part of the `columnType`:

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/User.ts"
@Entity()
export class User {

  @PrimaryKey()
  id!: number;

  @Property({ length: 50 })
  firstName!: string;

  @Property({ length: 50 })
  lastName!: string;

  @Property<User>({ length: 100, generated: cols => `(concat(${cols.firstName}, ' ', ${cols.lastName})) stored` })
  fullName!: string & Opt;

  @Property({ columnType: `varchar(100) generated always as (concat(first_name, ' ', last_name)) virtual` })
  fullName2!: string & Opt;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
export class User {

  @PrimaryKey()
  id!: number;

  @Property({ length: 50 })
  firstName!: string;

  @Property({ length: 50 })
  lastName!: string;

  @Property<User>({ length: 100, generated: cols => `(concat(${cols.firstName}, ' ', ${cols.lastName})) stored` })
  fullName!: string & Opt;

  @Property({ columnType: `varchar(100) generated always as (concat(first_name, ' ', last_name)) virtual` })
  fullName2!: string & Opt;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/User.ts"
export interface IUser {
  id: number;
  firstName: string;
  lastName: string;
  fullName: string & Opt;
  fullName2: string & Opt;
}

export const User = new EntitySchema<IUser>({
  name: 'User',
  properties: {
    id: { type: 'number', primary: true },
    firstName: { type: 'string', length: 50 },
    lastName: { type: 'string', length: 50 },
    fullName: {
      type: 'string',
      length: 100,
      generated: cols => `(concat(${cols.firstName}, ' ', ${cols.lastName})) stored`,
    },
    fullName2: {
      type: 'string',
      columnType: `varchar(100) generated always as (concat(first_name, ' ', last_name)) virtual`,
    },
  },
});
```

  </TabItem>
</Tabs>

To use a generated identity column in PostgreSQL, set the `generated` option to `identity`:

> To allow providing the value explicitly, use `generated: 'by default as identity'`.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/User.ts"
@Entity()
export class User {

  @PrimaryKey({ generated: 'identity' })
  id!: number;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
export class User {

  @PrimaryKey({ generated: 'identity' })
  id!: number;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/User.ts"
export interface IUser {
  id: number;
}

export const User = new EntitySchema<IUser>({
  name: 'User',
  properties: {
    id: { type: 'number', primary: true, generated: 'identity' },
  },
});
```

  </TabItem>
</Tabs>

## Examples of entity definition with various primary keys

### Using id as primary key (SQL drivers)

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
@Entity()
export class Book {

  @PrimaryKey()
  id!: number; // string is also supported

  @Property()
  title!: string;

  @ManyToOne(() => Author)
  author!: Author;

  @ManyToOne(() => Publisher, { ref: true, nullable: true })
  publisher?: Ref<Publisher>;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
export class Book {

  @PrimaryKey()
  id!: number; // string is also supported

  @Property()
  title!: string;

  @ManyToOne()
  author!: Author;

  @ManyToOne()
  publisher?: Ref<Publisher>;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
export interface Book {
  id: number;
  title: string;
  author: Author;
}

export const BookSchema = new EntitySchema<Book>({
  name: 'Book',
  properties: {
    id: { type: Number, primary: true },
    title: { type: String },
    author: { kind: 'm:1', entity: 'Author' },
    publisher: { kind: 'm:1', entity: 'Publisher', ref: true, nullable: true },
  },
});
```

  </TabItem>
</Tabs>

### Using UUID as primary key (SQL drivers)

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
import { v4 } from 'uuid';

@Entity()
export class Book {

  @PrimaryKey()
  uuid = v4();

  @Property()
  title!: string;

  @ManyToOne(() => Author)
  author!: Author;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
import { v4 } from 'uuid';

@Entity()
export class Book {

  @PrimaryKey()
  uuid = v4();

  @Property()
  title!: string;

  @ManyToOne()
  author!: Author;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
export interface IBook {
  uuid: string;
  title: string;
  author: Author;
}

export const Book = new EntitySchema<IBook>({
  name: 'Book',
  properties: {
    uuid: { type: 'uuid', onCreate: () => v4(), primary: true },
    title: { type: 'string' },
    author: { entity: () => Author, kind: 'm:1' },
  },
});
```

  </TabItem>
</Tabs>

### Using PostgreSQL built-in [gen_random_uuid](https://www.postgresql.org/docs/current/functions-uuid.html) function as primary key

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
@Entity()
export class Book {

  @PrimaryKey({ type: 'uuid', defaultRaw: 'gen_random_uuid()' })
  uuid: string;

  @Property()
  title!: string;

  @ManyToOne(() => Author)
  author!: Author;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
export class Book {

  @PrimaryKey({ type: 'uuid', defaultRaw: 'gen_random_uuid()' })
  uuid: string;

  @Property()
  title!: string;

  @ManyToOne()
  author!: Author;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
export class Book {
  uuid: string;
  title!: string;
  author!: Author;
}

export const BookSchema = new EntitySchema<Book>({
  class: Book,
  properties: {
    uuid: { type: 'uuid', defaultRaw: 'gen_random_uuid()', primary: true },
    title: { type: 'string' },
    author: { entity: () => Author, kind: 'm:1' },
  },
});
```

  </TabItem>
</Tabs>

### Using BigInt as primary key (MySQL and PostgreSQL)

Since v6, `bigint`s are represented by the native `BigInt` type, and as such, they don't require explicit type in the decorator options:

```ts
@PrimaryKey()
id: bigint;
```

You can also specify the target type you want your bigints to be mapped to:

```ts
@PrimaryKey({ type: new BigIntType('bigint') })
id1: bigint;

@PrimaryKey({ type: new BigIntType('string') })
id2: string;

@PrimaryKey({ type: new BigIntType('number') })
id3: number;
```

> JavaScript cannot represent all the possible values of a `bigint` when mapping to the `number` type - only values up to `Number.MAX_SAFE_INTEGER` (2^53 - 1) are safely supported.

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/CustomBaseEntity.ts"
@Entity()
export class Book {

  @PrimaryKey()
  id: bigint;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/CustomBaseEntity.ts"
@Entity()
export class Book {

  @PrimaryKey()
  id: bigint;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/CustomBaseEntity.ts"
properties: {
  id: { type: 'bigint' },
},
```

  </TabItem>
</Tabs>

If you want to use native `bigint`s, read the following guide: [Using native BigInt PKs](./using-bigint-pks.md).

### Example of Mongo entity

<Tabs
groupId="entity-def"
defaultValue="reflect-metadata"
values={[
{label: 'reflect-metadata', value: 'reflect-metadata'},
{label: 'ts-morph', value: 'ts-morph'},
{label: 'EntitySchema', value: 'entity-schema'},
]
}>
<TabItem value="reflect-metadata">

```ts title="./entities/Book.ts"
@Entity()
export class Book {

  @PrimaryKey()
  _id!: ObjectId;

  @SerializedPrimaryKey()
  id!: string; // string variant of PK, will be handled automatically

  @Property()
  title!: string;

  @ManyToOne(() => Author)
  author!: Author;

}
```

  </TabItem>
  <TabItem value="ts-morph">

```ts title="./entities/Book.ts"
@Entity()
export class Book {

  @PrimaryKey()
  _id!: ObjectId;

  @SerializedPrimaryKey()
  id!: string; // string variant of PK, will be handled automatically

  @Property()
  title!: string;

  @ManyToOne()
  author!: Author;

}
```

  </TabItem>
  <TabItem value="entity-schema">

```ts title="./entities/Book.ts"
export interface IBook {
  _id: ObjectId;
  id: string;
  title: string;
  author: Author;
}

export const Book = new EntitySchema<IBook>({
  name: 'Book',
  properties: {
    _id: { type: 'ObjectId', primary: true },
    id: { type: String, serializedPrimaryKey: true },
    title: { type: String },
  },
});
```

  </TabItem>
</Tabs>

### Using MikroORM's BaseEntity (previously WrappedEntity)

From v4 `BaseEntity` class is provided with `init`, `isInitialized`, `assign` and other methods that are otherwise available via the `wrap()` helper.

> Usage of the `BaseEntity` is optional.

```ts
import { BaseEntity } from '@mikro-orm/core';

@Entity()
export class Book extends BaseEntity {

  @PrimaryKey()
  id!: number;

  @Property()
  title!: string;

  @ManyToOne()
  author!: Author;

}

const book = new Book();
console.log(book.isInitialized()); // true
```

Having the entities set up, we can now start [using entity manager](./entity-manager.md) and [repositories](./repositories.md) as described in following sections.
