嵌入式实体

通过使用embedded columns,可以减少应用程序中的重复(使用组合而不是继承)。

嵌入列是一个列,它接受具有自己列的类,并将这些列合并到当前实体的数据库表中。

例如:

假设我们有UserEmployeeStudent实体。

这些属性都有少量的共同点,first namelast name属性。

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
@Entity()
export class User {
@PrimaryGeneratedColumn()
id: string;
@Column()
firstName: string;
@Column()
lastName: string;
@Column()
isActive: boolean;
}
import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
@Entity()
export class Employee {
@PrimaryGeneratedColumn()
id: string;
@Column()
firstName: string;
@Column()
lastName: string;
@Column()
salary: string;
}
import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
@Entity()
export class Student {
@PrimaryGeneratedColumn()
id: string;
@Column()
firstName: string;
@Column()
lastName: string;
@Column()
faculty: string;
}

我们可以做的是通过创建一个包含firstNamelastName的新类:

import {Entity, Column} from "typeorm";
export class Name {
@Column()
first: string;
@Column()
last: string;
}

然后"connect"实体中的这些列:

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
import {Name} from "./Name";
@Entity()
export class User {
@PrimaryGeneratedColumn()
id: string;
@Column(type => Name)
name: Name;
@Column()
isActive: boolean;
}
import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
import {Name} from "./Name";
@Entity()
export class Employee {
@PrimaryGeneratedColumn()
id: string;
@Column(type => Name)
name: Name;
@Column()
salary: number;
}
import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";
import {Name} from "./Name";
@Entity()
export class Student {
@PrimaryGeneratedColumn()
id: string;
@Column(type => Name)
name: Name;
@Column()
faculty: string;
}

Name实体中定义的所有列将合并为useremployeestudent

+-------------+--------------+----------------------------+
| user |
+-------------+--------------+----------------------------+
| id | int(11) | PRIMARY KEY AUTO_INCREMENT |
| nameFirst | varchar(255) | |
| nameLast | varchar(255) | |
| isActive | boolean | |
+-------------+--------------+----------------------------+
+-------------+--------------+----------------------------+
| employee |
+-------------+--------------+----------------------------+
| id | int(11) | PRIMARY KEY AUTO_INCREMENT |
| nameFirst | varchar(255) | |
| nameLast | varchar(255) | |
| salary | int(11) | |
+-------------+--------------+----------------------------+
+-------------+--------------+----------------------------+
| student |
+-------------+--------------+----------------------------+
| id | int(11) | PRIMARY KEY AUTO_INCREMENT |
| nameFirst | varchar(255) | |
| nameLast | varchar(255) | |
| faculty | varchar(255) | |
+-------------+--------------+----------------------------+

这种方式可以减少实体类中的代码重复。 你可以根据需要在嵌入式类中使用尽可能多的列(或关系)。 甚至可以在嵌入式类中嵌套嵌套列。