Class MysqlAdapter

Whether or not this dialect supports the returning in inserts updates and deletes.

Whether or not this dialect supports transactional DDL.

If this is true, migrations are executed inside a transaction.

This method is used to acquire a lock for the migrations so that it's not possible for two migration operations to run in parallel.

Most dialects have explicit locks that can be used, like advisory locks in PostgreSQL and the get_lock function in MySQL.

If the dialect doesn't have explicit locks the lockTable created by Kysely can be used instead. You can access it through the options object. The lock table has two columns id and is_locked and there's only one row in the table whose id is lockRowId. is_locked is an integer. Kysely takes care of creating the lock table and inserting the one single row to it before this method is executed. If the dialect supports schemas and the user has specified a custom schema in their migration settings, the options object also contains the schema name in lockTableSchema.

Here's an example of how you might implement this method for a dialect that doesn't have explicit locks but supports FOR UPDATE row locks and transactional DDL:

{
  async acquireMigrationLock(db, options): Promise<void> {
    const queryDb = options.lockTableSchema
      ? db.withSchema(options.lockTableSchema)
      : db

    // Since our imaginary dialect supports transactional DDL and has
    // row locks, we can simply take a row lock here and it will guarantee
    // all subsequent calls to this method from other transactions will
    // wait until this transaction finishes.
    await queryDb
      .selectFrom(options.lockTable)
      .selectAll()
      .where('id', '=', options.lockRowId)
      .forUpdate()
      .execute()
  }
}
Copy

If supportsTransactionalDdl is true then the db passed to this method is a transaction inside which the migrations will be executed. Otherwise db is a single connection (session) that will be used to execute the migrations.

Releases the migration lock. See acquireMigrationLock.

If supportsTransactionalDdl is true then the db passed to this method is a transaction inside which the migrations were executed. Otherwise db is a single connection (session) that was used to execute the migrations and the acquireMigrationLock call.