Concrete Table Inheritance

You can reduce duplication in your code by using entity inheritance patterns. The simplest and the most effective is concrete table inheritance.

For example, you have Photo, Question, Post entities:

@Entity()
export class Photo {
    @PrimaryGeneratedColumn()
    id: number

    @Column()
    title: string

    @Column()
    description: string

    @Column()
    size: string
}

@Entity()
export class Question {
    @PrimaryGeneratedColumn()
    id: number

    @Column()
    title: string

    @Column()
    description: string

    @Column()
    answersCount: number
}

@Entity()
export class Post {
    @PrimaryGeneratedColumn()
    id: number

    @Column()
    title: string

    @Column()
    description: string

    @Column()
    viewCount: number
}

As you can see all those entities have common columns: id, title, description. To reduce duplication and produce a better abstraction we can create a base class called Content for them:

export abstract class Content {
    @PrimaryGeneratedColumn()
    id: number

    @Column()
    title: string

    @Column()
    description: string
}

@Entity()
export class Photo extends Content {
    @Column()
    size: string
}

@Entity()
export class Question extends Content {
    @Column()
    answersCount: number
}

@Entity()
export class Post extends Content {
    @Column()
    viewCount: number
}

All columns (relations, embeds, etc.) from parent entities (parent can extend other entity as well) will be inherited and created in final entities.

This example will create 3 tables – photo, question and post.