[WIP] Add new mode to wrap each migration in transaction

[garbles]

Addresses #2693

Creates a new, backwards compatible mode for running migrations each in their own transaction. This behaviour is what I think most expect as default from an ORM, so running all migrations in a single transaction seems odd. Using a single transaction also does not allow you to do certain things (in Postgres at least) if you expect to be able to run all migrations at once.

For example, if you have the following two migrations, you can never run all of from scratch.

import { MigrationInterface, QueryRunner } from "typeorm";

export class CreateUuidExtension1544044606093 implements MigrationInterface {
  public up(queryRunner: QueryRunner): Promise<any> {
    return queryRunner.query(`CREATE EXTENSION IF NOT EXISTS "uuid-ossp";`);
  }

  public down(queryRunner: QueryRunner): Promise<any> {
    return queryRunner.query('DROP EXTENSION "uuid-ossp"');
  }
}

import { MigrationInterface, QueryRunner, Table } from "typeorm";

export class CreateUsers1543965157399 implements MigrationInterface {
  public up(queryRunner: QueryRunner): Promise<any> {
    return queryRunner.createTable(
      new Table({
        name: "users",
        columns: [
          { name: "id", type: "uuid", isPrimary: true, default: "uuid_generate_v4()" },
        ]
      })
    );
  }

  public down(queryRunner: QueryRunner): Promise<any> {
    return queryRunner.dropTable("users");
  }
}

The error is function uuid_generate_v4() does not exist because extensions cannot be referenced from the same transaction which they are created.

Changes to the -t flag to accept: all (run all migrations in a single transaction), each (run each migration in a separate transaction), none (run all migrations without transactions) or false (same as none).

TODO:

• Add new tests for 'each' mode
• Clean up code

[pleerock]

I think we can simplify it and just call it transaction

[MatthiasKunnen]

I would prefer transactionMode or a variant thereof in this case. When a parameter is called transaction I would expect to pass an object of type Transaction.

[pleerock]

okay...

[pleerock]

looks like this block is repeated 3 times, probably we should extract it into separate method

[pleerock]

Thanks for the contribution!

Seems tests are failing, can you please fix them?
Also can you please address comments I have left?

[mordof]

@garbles is this something you're going to finish up? this is a feature I'd like to see added; if you're not interested in finishing this i'd be glad to take care of the feedback given to get this ready.

[garbles]

@mordof hey! Sorry I haven't had time to finish it. Please feel free to take on this PR!