# Separating Entity Definition ## Defining Schemas[​](#defining-schemas "Direct link to Defining Schemas") You can define an entity and its columns right in the model, using decorators. But some people prefer to define an entity and its columns inside separate files which are called "entity schemas" in TypeORM. Simple definition example: ``` import { EntitySchema } from "typeorm" export const CategoryEntity = new EntitySchema({ name: "category", columns: { id: { type: Number, primary: true, generated: true, }, name: { type: String, }, }, }) ``` Example with relations: ``` import { EntitySchema } from "typeorm" export const PostEntity = new EntitySchema({ name: "post", columns: { id: { type: Number, primary: true, generated: true, }, title: { type: String, }, text: { type: String, }, }, relations: { categories: { type: "many-to-many", target: "category", // CategoryEntity }, }, }) ``` Complex example: ``` import { EntitySchema } from "typeorm" export const PersonSchema = new EntitySchema({ name: "person", columns: { id: { primary: true, type: "int", generated: "increment", }, firstName: { type: String, length: 30, }, lastName: { type: String, length: 50, nullable: false, }, age: { type: Number, nullable: false, }, countryCode: { type: String, length: 2, foreignKey: { target: "countries", // CountryEntity inverseSide: "code", }, }, cityId: { type: Number, foreignKey: { target: "cities", // CityEntity }, }, }, checks: [ { expression: `"firstName" <> 'John' AND "lastName" <> 'Doe'` }, { expression: `"age" > 18` }, ], indices: [ { name: "IDX_TEST", unique: true, columns: ["firstName", "lastName"], }, ], uniques: [ { name: "UNIQUE_TEST", columns: ["firstName", "lastName"], }, ], foreignKeys: [ { target: "cities", // CityEntity columnNames: ["cityId", "countryCode"], referencedColumnNames: ["id", "countryCode"], }, ], }) ``` If you want to make your entity typesafe, you can define a model and specify it in schema definition: ``` import { EntitySchema } from "typeorm" export interface Category { id: number name: string } export const CategoryEntity = new EntitySchema({ name: "category", columns: { id: { type: Number, primary: true, generated: true, }, name: { type: String, }, }, }) ``` ## Extending Schemas[​](#extending-schemas "Direct link to Extending Schemas") When using the `Decorator` approach it is easy to `extend` basic columns to an abstract class and simply extend this. For example, your `id`, `createdAt` and `updatedAt` columns may be defined in such a `BaseEntity`. For more details, see the documentation on [concrete table inheritance](https://typeorm.io/docs/entity/entity-inheritance.md#concrete-table-inheritance). When using the `EntitySchema` approach, this is not possible. However, you can use the `Spread Operator` (`...`) to your advantage. Reconsider the `Category` example from above. You may want to `extract` basic column descriptions and reuse it across your other schemas. This may be done in the following way: ``` import { EntitySchemaColumnOptions } from "typeorm" export const BaseColumnSchemaPart = { id: { type: Number, primary: true, generated: true, } as EntitySchemaColumnOptions, createdAt: { name: "created_at", type: "timestamp with time zone", createDate: true, } as EntitySchemaColumnOptions, updatedAt: { name: "updated_at", type: "timestamp with time zone", updateDate: true, } as EntitySchemaColumnOptions, } ``` Now you can use the `BaseColumnSchemaPart` in your other schema models, like this: ``` export const CategoryEntity = new EntitySchema({ name: "category", columns: { ...BaseColumnSchemaPart, // the CategoryEntity now has the defined id, createdAt, updatedAt columns! // in addition, the following NEW fields are defined name: { type: String, }, }, }) ``` You can use embedded entities in schema models, like this: ``` export interface Name { first: string last: string } export const NameEntitySchema = new EntitySchema({ name: "name", columns: { first: { type: "varchar", }, last: { type: "varchar", }, }, }) export interface User { id: string name: Name isActive: boolean } export const UserEntitySchema = new EntitySchema({ name: "user", columns: { id: { primary: true, generated: "uuid", type: "uuid", }, isActive: { type: "boolean", }, }, embeddeds: { name: { schema: NameEntitySchema, prefix: "name_", }, }, }) ``` Be sure to add the `extended` columns also to the `Category` interface (e.g., via `export interface Category extend BaseEntity`). ### Single Table Inheritance[​](#single-table-inheritance "Direct link to Single Table Inheritance") In order to use [Single Table Inheritance](https://typeorm.io/docs/entity/entity-inheritance.md#single-table-inheritance): 1. Add the `inheritance` option to the **parent** class schema, specifying the inheritance pattern ("STI") and the **discriminator** column, which will store the name of the *child* class on each row 2. Set the `type: "entity-child"` option for all **children** classes' schemas, while extending the *parent* class columns using the spread operator syntax described above ``` // entity.ts export abstract class Base { id!: number type!: string createdAt!: Date updatedAt!: Date } export class A extends Base { constructor(public a: boolean) { super() } } export class B extends Base { constructor(public b: number) { super() } } export class C extends Base { constructor(public c: string) { super() } } ``` ``` // schema.ts const BaseSchema = new EntitySchema({ target: Base, name: "Base", columns: { id: { type: Number, primary: true, generated: "increment", }, type: { type: String, }, createdAt: { type: Date, createDate: true, }, updatedAt: { type: Date, updateDate: true, }, }, // NEW: Inheritance options inheritance: { pattern: "STI", column: "type", }, }) const ASchema = new EntitySchema({ target: A, name: "A", type: "entity-child", // When saving instances of 'A', the "type" column will have the value // specified on the 'discriminatorValue' property discriminatorValue: "my-custom-discriminator-value-for-A", columns: { ...BaseSchema.options.columns, a: { type: Boolean, }, }, }) const BSchema = new EntitySchema({ target: B, name: "B", type: "entity-child", discriminatorValue: undefined, // Defaults to the class name (e.g. "B") columns: { ...BaseSchema.options.columns, b: { type: Number, }, }, }) const CSchema = new EntitySchema({ target: C, name: "C", type: "entity-child", discriminatorValue: "my-custom-discriminator-value-for-C", columns: { ...BaseSchema.options.columns, c: { type: String, }, }, }) ``` ## Using Schemas to Query / Insert Data[​](#using-schemas-to-query--insert-data "Direct link to Using Schemas to Query / Insert Data") Of course, you can use the defined schemas in your repositories or entity manager as you would use the decorators. Consider the previously defined `Category` example (with its `Interface` and `CategoryEntity` schema) in order to get some data or manipulate the database. ``` // request data const categoryRepository = dataSource.getRepository(CategoryEntity) const category = await categoryRepository.findOneBy({ id: 1, }) // category is properly typed! // insert a new category into the database const categoryDTO = { // note that the ID is autogenerated; see the schema above name: "new category", } const newCategory = await categoryRepository.save(categoryDTO) ```