typeorm: what is the difference between getRepository() and getConnection()?

https://typeorm.io/#/select-query-builder/how-to-create-and-use-a-querybuilder

There are several ways how you can create a Query Builder:

Using connection:

import {getConnection} from "typeorm";

const user = await getConnection()
    .createQueryBuilder()
    .select("user")
    .from(User, "user")
    .where("user.id = :id", { id: 1 })
    .getOne();

Using entity manager:

import {getManager} from "typeorm";

const user = await getManager()
    .createQueryBuilder(User, "user")
    .where("user.id = :id", { id: 1 })
    .getOne();

Using repository:

import {getRepository} from "typeorm";

const user = await getRepository(User)
    .createQueryBuilder("user")
    .where("user.id = :id", { id: 1 })
    .getOne();

The documentation never explains the difference among these methods. When to use each method?

Solution

Take a look at the source code:

getConnection():

/**
 * Gets connection from the connection manager.
 * If connection name wasn't specified, then "default" connection will be retrieved.
 *
 * @deprecated
 */
export function getConnection(connectionName: string = "default"): DataSource {
    return getConnectionManager().get(connectionName)
}

getRepository()

/**
 * Gets repository for the given entity class.
 *
 * @deprecated
 */
export function getRepository<Entity extends ObjectLiteral>(
    entityClass: EntityTarget<Entity>,
    connectionName: string = "default",
): Repository<Entity> {
    return getConnectionManager()
        .get(connectionName)
        .getRepository<Entity>(entityClass)
}

getManager()

/**
 * Gets entity manager from the connection.
 * If connection name wasn't specified, then "default" connection will be retrieved.
 *
 * @deprecated
 */
export function getManager(connectionName: string = "default"): EntityManager {
    return getConnectionManager().get(connectionName).manager
}

getConnection() returns a DataSource, getRepository() returns a Repository and getManager() returns an EntityManager. All of them have the createQueryBuilder() method, see Repository.ts#L77, DataSource.ts#L555 and EntityManager.ts#L194

So the differences between them are: