Transactions

The transact function and with-transaction macro were briefly mentioned in the Getting Started section but we'll go into more detail here.

Although (transact connectable thunk) is available, it is expected that you will mostly use (with-transaction [tx connectable] body...) when you want to execute multiple SQL operations in the context of a single transaction so that is what this section focuses on.

By default, all connections that next.jdbc creates are automatically committable, i.e., as each operation is performed, the effect is committed to the database directly before the next operation is performed. Any exceptions only cause the current operation to be aborted -- any prior operations have already been committed.

It is possible to tell next.jdbc to create connections that do not automatically commit operations: pass {:auto-commit false} as part of the options map to anything that creates a connection (including get-connection itself). You can then decide when to commit or rollback by calling .commit or .rollback on the connection object itself. You can also create save points ((.setSavePoint con), (.setSavePoint con name)) and rollback to them ((.rollback con save-point)). You can also change the auto-commit state of an open connection at any time ((.setAutoCommit con on-off)).

next.jdbc's transaction handling provides a convenient baseline for either committing a group of operations if they all succeed or rolling them all back if any of them fails, by throwing an exception. You can either do this on an existing connection -- and next.jdbc will try to restore the state of the connection after the transaction completes -- or by providing a datasource and letting with-transaction create and manage its own connection:

(jdbc/with-transaction [tx my-datasource]
  (jdbc/execute! tx ...)
  (jdbc/execute! tx ...))

You can also provide an options map as the third element of the binding vector (or the third argument to the transact function). The following options are supported:

• :isolation -- the isolation level for this transaction (see All The Options for specifics),
• :read-only -- set the transaction into read-only mode (if true),
• :rollback-only -- set the transaction to always rollback, even on success (if true).

The latter can be particularly useful in tests, to run a series of SQL operations during a test and then roll them all back at the end.

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