`.transaction()`

Fetch a preconfigured, deferred object hooked up to the sails-mysql or sails-postgresql adapter (and consequently the appropriate driver).

usage

await datastore.transaction(during);

var result = await datastore.transaction(during);

Usage

	Argument	Type	Details
1	during	((function))	See parameters in the "`during` usage" table below.

During

	Argument	Type	Details
1	db	((ref))	The leased (transactional) database connection. (See `.usingConnection()` for more information on what to do with this.)

Note that prior to Sails 1.1.0, the recommended usage of .transaction() expected your "during" code to call a callback (proceed) when it finished. This is no longer necessary as long as you do not actually include a second argument in the function signature of your "during" code.

Result

Type	Details
((Ref?))	The optional result data sent back from `during`. In other words, if in your `during` function you did `return 'foo';`, then this will be `'foo'`.

Errors

Name	Type	When?
UsageError	((Error))	Thrown if something invalid was passed in.
AdapterError	((Error))	Thrown if something went wrong in the database adapter.
Error	((Error))	Thrown if anything else unexpected happens.

See Concepts > Models and ORM > Errors for examples of negotiating errors in Sails and Waterline.

Example

Subtract the specified amount from one user's balance and add it to another's.

javascript

// e.g. in an action:

var flaverr = require('flaverr');

await sails.getDatastore()
.transaction(async (db)=> {

  var myAccount = await BankAccount.findOne({ owner: this.req.session.userId })
  .usingConnection(db);
  if (!myAccount) {
    throw new Error('Consistency violation: Database is corrupted-- logged in user record has gone missing');
  }

  var recipientAccount = await BankAccount.findOne({ owner: inputs.recipientId }).usingConnection(db)
  if (!recipientAccount) {
    throw flaverr('E_NO_SUCH_RECIPIENT', new Error('There is no recipient with that id'));
  }

  // Do the math to subtract from the logged-in user's account balance,
  // and add to the recipient's bank account balance.
  var myNewBalance = myAccount.balance - inputs.amount;

  // If this would put the logged-in user's account balance below zero,
  // then abort.  (The transaction will be rolled back automatically.)
  if (myNewBalance < 0) {
    throw flaverr('E_INSUFFICIENT_FUNDS', new Error('Insufficient funds'));
  }

  // Update the current user's bank account
  await BankAccount.update({ owner: this.req.session.userId })
  .set({
    balance: myNewBalance
  })
  .usingConnection(db);

  // Update the recipient's bank account
  await BankAccount.update({ owner: inputs.recipientId })
  .set({
    balance: recipientAccount.balance + inputs.amount
  })
  .usingConnection(db);
})
.intercept('E_INSUFFICIENT_FUNDS', ()=>'badRequest')
.intercept('E_NO_SUCH_RECIPIENT', ()=>'notFound');

Note that the example above is just a demonstration; in practice, this kind of increment/decrement logic should also include row-level locking. Unsure?.