Creating generic repository using TypeORM

Question

I'm using typeorm and I want to create a generic repository:

import "reflect-metadata";
import { DBManager } from './db-manager';
import { Photo } from './entities/Photo';
import { createConnection, Connection } from "typeorm";

class GenericRepository<T> {
private connection: DBManager;
constructor(connection: DBManager) {
    this.connection = connection;
}

public list(): T[] {
    let result: T[] = [];
    this.connection.connect().then(async  connection => {
        result = await <Promise<T[]>>(connection.entityManager.find(T));
    });
    return result;
 }
}

let genericReposity = new GenericRepository<Photo>(new DBManager());
genericReposity.list();

This code of course doesn't woork and complains on find method that can not find name T

T should be my entity but I don't know how to achieve this

I edited my example hope it is more clear now but basically .find(T) complains that can not fine name T T should be the Photo but since I want to my class be a generic class so I need somehow to pass the type to my generic method — user4092086
– user4092086, Commented Nov 26, 2016 at 16:48

Gao Shenghan · Accepted Answer · 2018-05-08 04:28:15Z

8

Generics in TypeScript are only in compile-type and all information about your generics types are removed in output javascript code. Thats why its not possible to do what you want. Its only possible if you explicitly specify a type to your generic repository, for example via constructor:

import "reflect-metadata";
import { DBManager } from './db-manager';
import { Photo } from './entities/Photo';
import { createConnection, Connection } from "typeorm";

export type ObjectType<T> = { new (): T } | Function;

class GenericRepository<T> {
    private connection: DBManager;
    private type: ObjectType<T>;
    constructor(type: ObjectType<T>, connection: DBManager) {
        this.type = type;        
        this.connection = connection;
}

public list(): T[] {
    let result: T[] = [];
    this.connection.connect().then(async  connection => {
        result = await <Promise<T[]>>(connection.entityManager.find(this.type));
    });
    return result;
 }
}

let genericReposity = new GenericRepository(Photo, new DBManager());
genericReposity.list();

Also side note, you probably don't want to connect to the database each time you request list of entities. So I recommend to redesign your class.

edited May 8, 2018 at 4:28

Gao Shenghan

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answered Nov 26, 2016 at 17:35

pleerock

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4 Comments

user4092086 Over a year ago

Tried this solution too but still complains [ts] Argument of type 'T' is not assignable to parameter of type 'ObjectType'. Type 'T' is not assignable to type 'new () => {}'.

user4092086 Over a year ago

For the connection actually i'm using injectors but didn't bring it here

pleerock Over a year ago

@user4092086 I made small changes, take a look on them. Also take a look on github.com/typeorm/typeorm-typedi-extensions this may help you to organize your code

user4092086 Over a year ago

Thanks this works But I'm wonder how can I bind ObjectType<T> in my injector?

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