||A migration for the
||Represents a database "migration", which can be composed together with other migrations across multiple components to initialise a database and update it with updates.
||Represents an instance of a query, which can be executed and results fetched.
||Represents a database that stores the state of updated tables, and uses either replicated database hosts based on the type of query.
||Represents a query which may have used a replicated connection.
||Represents an instance of a single database connection.