Docs Menu

Write Transactions - Android SDK

On this page

  • Run a Transaction

Realm Database uses a highly efficient storage engine to persist objects. You can create objects in a realm, update objects in a realm, and eventually delete objects from a realm. Because these operations modify the state of the realm, we call them writes.

Realm handles writes in terms of transactions. A transaction is a list of read and write operations that Realm treats as a single indivisible operation. In other words, a transaction is all or nothing: either all of the operations in the transaction succeed or none of the operations in the transaction take effect.

Note

All writes must happen in a transaction.

A realm allows only one open write transaction at a time. Realm blocks other writes on other threads until the open transaction is complete. Consequently, there is no race condition when reading values from the realm within a transaction.

When you are done with your transaction, Realm either commits it or cancels it:

  • When Realm commits a transaction, Realm writes all changes to disk. For synced realms, Realm queues the change for synchronization with MongoDB Realm.
  • When Realm cancels a write transaction or an operation in the transaction causes an error, all changes are discarded (or "rolled back").

Realm represents each transaction as a callback function that contains zero or more read and write operations. To run a transaction, define a transaction callback and pass it to the realm's write method. Within this callback, you are free to create, read, update, and delete on the realm. If the code in the callback throws an exception when Realm runs it, Realm cancels the transaction. Otherwise, Realm commits the transaction immediately after the callback.

Example

The following code shows how to run a transaction with executeTransaction() or executeTransactionAsync(). If the code in the callback throws an exception, Realm cancels the transaction. Otherwise, Realm commits the transaction.

Tip
See also:

On this page

Give Feedback
MongoDB logo
© 2021 MongoDB, Inc.

About

  • Careers
  • Legal Notices
  • Privacy Notices
  • Security Information
  • Trust Center
© 2021 MongoDB, Inc.