View Entities

• What is View Entity?
• View Entity columns
• Complete example

What is View Entity?

View entity is a class that maps to a database view.You can create a view entity by defining a new class and mark it with @ViewEntity():

@ViewEntity() accepts following options:

• name - view name. If not specified, then view name is generated from entity class name.
• database - database name in selected DB server.
• schema - schema name.
• expression - view definition. Required parameter.

expression can be string with properly escaped columns and tables, depend on database used (postgres in example):

@ViewEntity({ 
    expression: `
        SELECT "post"."id" "id", "post"."name" AS "name", "category"."name" AS "categoryName"
        FROM "post" "post"
        LEFT JOIN "category" "category" ON "post"."categoryId" = "category"."id"
    `
})

or an instance of QueryBuilder

@ViewEntity({ 
    expression: (connection: Connection) => connection.createQueryBuilder()
        .select("post.id", "id")
        .addSelect("post.name", "name")
        .addSelect("category.name", "categoryName")
        .from(Post, "post")
        .leftJoin(Category, "category", "category.id = post.categoryId")
})

Note: parameter binding is not supported due to drivers limitations. Use the literal parameters instead.

@ViewEntity({ 
    expression: (connection: Connection) => connection.createQueryBuilder()
        .select("post.id", "id")
        .addSelect("post.name", "name")
        .addSelect("category.name", "categoryName")
        .from(Post, "post")
        .leftJoin(Category, "category", "category.id = post.categoryId")
        .where("category.name = :name", { name: "Cars" })  // <-- this is wrong
        .where("category.name = 'Cars'")                   // <-- and this is right
})

Each view entity must be registered in your connection options:

import {createConnection, Connection} from "typeorm";
import {UserView} from "./entity/UserView";
const connection: Connection = await createConnection({
    type: "mysql",
    host: "localhost",
    port: 3306,
    username: "test",
    password: "test",
    database: "test",
    entities: [UserView]
});

Or you can specify the whole directory with all entities inside - and all of them will be loaded:

import {createConnection, Connection} from "typeorm";
const connection: Connection = await createConnection({
    type: "mysql",
    host: "localhost",
    port: 3306,
    username: "test",
    password: "test",
    database: "test",
    entities: ["entity/*.js"]
});

View Entity columns

To map data from view into the correct entity columns you must mark entity columns with @ViewColumn()decorator and specify these columns as select statement aliases.

example with string expression definition:

import {ViewEntity, ViewColumn} from "typeorm";
@ViewEntity({ 
    expression: `
        SELECT "post"."id" AS "id", "post"."name" AS "name", "category"."name" AS "categoryName"
        FROM "post" "post"
        LEFT JOIN "category" "category" ON "post"."categoryId" = "category"."id"
    `
})
export class PostCategory {
    @ViewColumn()
    id: number;
    @ViewColumn()
    name: string;
    @ViewColumn()
    categoryName: string;
}

example using QueryBuilder:

import {ViewEntity, ViewColumn} from "typeorm";
@ViewEntity({ 
    expression: (connection: Connection) => connection.createQueryBuilder()
        .select("post.id", "id")
        .addSelect("post.name", "name")
        .addSelect("category.name", "categoryName")
        .from(Post, "post")
        .leftJoin(Category, "category", "category.id = post.categoryId")
})
export class PostCategory {
    @ViewColumn()
    id: number;
    @ViewColumn()
    name: string;
    @ViewColumn()
    categoryName: string;
}

Complete example

Let create two entities and a view containing aggregated data from these entities:

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
@Entity()
export class Category {
    @PrimaryGeneratedColumn()
    id: number;
    @Column()
    name: string;
}

import {Entity, PrimaryGeneratedColumn, Column, ManyToOne, JoinColumn} from "typeorm";
import {Category} from "./Category";
@Entity()
export class Post {
    @PrimaryGeneratedColumn()
    id: number;
    @Column()
    name: string;
    @Column()
    categoryId: number;
    @ManyToOne(() => Category)
    @JoinColumn({ name: "categoryId" })
    category: Category;
}

import {ViewEntity, ViewColumn} from "typeorm";
@ViewEntity({ 
    expression: (connection: Connection) => connection.createQueryBuilder()
        .select("post.id", "id")
        .addSelect("post.name", "name")
        .addSelect("category.name", "categoryName")
        .from(Post, "post")
        .leftJoin(Category, "category", "category.id = post.categoryId")
})
export class PostCategory {
    @ViewColumn()
    id: number;
    @ViewColumn()
    name: string;
    @ViewColumn()
    categoryName: string;
}

then fill these tables with data and request all data from PostCategory view:

import {getManager} from "typeorm";
import {Category} from "./entity/Category";
import {Post} from "./entity/Post";
import {PostCategory} from "./entity/PostCategory";
const entityManager = getManager();
const category1 = new Category();
category1.name = "Cars";
await entityManager.save(category1);
const category2 = new Category();
category2.name = "Airplanes";
await entityManager.save(category2);
const post1 = new Post();
post1.name = "About BMW";
post1.categoryId = category1.id;
await entityManager.save(post1);
const post2 = new Post();
post2.name = "About Boeing";
post2.categoryId = category2.id;
await entityManager.save(post2);
const postCategories = await entityManager.find(PostCategory);
const postCategory = await entityManager.findOne(PostCategory, { id: 1 });

the result in postCategories will be:

[ PostCategory { id: 1, name: 'About BMW', categoryName: 'Cars' },
  PostCategory { id: 2, name: 'About Boeing', categoryName: 'Airplanes' } ]

and in postCategory:

PostCategory { id: 1, name: 'About BMW', categoryName: 'Cars' }