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Working with Query Runner

What is QueryRunner

Each new QueryRunner instance takes a single connection from connection pool, if RDBMS supports connection pooling. For databases not supporting connection pools, it uses the same connection across data source.

Creating a new QueryRunner instance

Use createQueryRunner method to create a new QueryRunner:
const queryRunner = dataSource.createQueryRunner()

Using QueryRunner

After you create a new instance of QueryRunner use connect method to actually obtain a connection from the connection pool:
const queryRunner = dataSource.createQueryRunner()
await queryRunner.connect()
Important: make sure to release it when it is not needed anymore to make it available to the connection pool again:
await queryRunner.release()
After connection is released it is not possible to use the query runner methods.
QueryRunner has bunch of methods you can use, it also has its own EntityManager instance, which you can use through manager property in order to run EntityManager methods on a particular database connection used by QueryRunner instance:
const queryRunner = connection.createQueryRunner()
​
// take a connection from the connection pool
await queryRunner.connect()
​
// use this particular connection to execute queries
const users = await queryRunner.manager.find(User)
​
// don't forget to release connection after you are done using it
await queryRunner.release()