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Fundamentals

Transactions

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  • Overview
  • Methods
  • Example
  • Additional Information
  • API Documentation

Overview

In this guide, you can learn how to use the MongoDB Go Driver to perform transactions. Transactions allow you to run a series of operations that do not change any data until the transaction is committed. If any operation in the transaction returns an error, the driver cancels the transaction and discards all data changes before they ever become visible.

In MongoDB, transactions run within logical sessions. A session is a grouping of related read or write operations that you intend to run sequentially. Sessions enable causal consistency for a group of operations or allow you to execute operations in an ACID transaction. MongoDB guarantees that the data involved in your transaction operations remains consistent, even if the operations encounter unexpected errors.

When using the Go driver, you can create a new session from a Client instance as a Session type. We recommend that you reuse your client for multiple sessions and transactions instead of instantiating a new client each time.

Warning

You should use a Session only with the Client (or associated Database or Collection) that created it. Using a Session with a different Client results in operation errors.

Warning

Implementations of Session are not safe for concurrent use by multiple goroutines.

Methods

After you start a session by using the StartSession() method, you can modify the session state by using the method set provided by the Session interface. The following table describes these methods:

Method
Description
StartTransaction()
Starts a new transaction, configured with the given options, on this session. Returns an error if there is already a transaction in progress for the session. To learn more about this method, see the startTransaction() page in the Server manual.

Parameter: TransactionOptions
Return Type: error
AbortTransaction()
Ends the active transaction for this session. Returns an error if there is no active transaction for the session or the transaction has been committed or ended. To learn more about this method, see the abortTransaction() page in the Server manual.

Parameter: Context
Return Type: error
CommitTransaction()
Commits the active transaction for this session. Returns an error if there is no active transaction for the session or if the transaction was ended. To learn more about this method, see the commitTransaction() page in the Server manual.

Note

Retrying a Transaction

The CommitTransaction() method is an idempotent function, which means that you can attempt to commit a transaction multiple times without changing data after the first successful commit.

A transaction can succeed but return an error with the UnknownTransactionCommitResult label. If you rerun the CommitTransaction() method after receiving this error, your data is not changed by the repeat attempts.


Parameter: Context
Return Type: error
WithTransaction()
Starts a transaction on this session and runs the fn callback.

Parameters: Context, fn func(ctx SessionContext), TransactionOptions
Return Type: interface{}, error
EndSession()
Ends any existing transactions and closes the session.

Parameter: Context
Return Type: none

The Session interface also has methods to retrieve session properties and modify mutable session properties. Find more information in the API documentation.

Example

The following example shows how you can create a session, create a transaction, and commit a multi-document insert operation through the following steps:

  1. Create a session from the client using the StartSession() method.

  2. Use the WithTransaction() method to start a transaction.

  3. Insert multiple documents. The WithTransaction() method executes the insert and commits the transaction. If any operation results in errors, WithTransaction() handles aborting the transaction.

  4. Close the transaction and session using the EndSession() method.

wc := writeconcern.New(writeconcern.WMajority())
txnOptions := options.Transaction().SetWriteConcern(wc)
session, err := client.StartSession()
if err != nil {
	panic(err)
}
defer session.EndSession(context.TODO())
result, err := session.WithTransaction(context.TODO(), func(ctx mongo.SessionContext) (interface{}, error) {
	result, err := coll.InsertMany(ctx, []interface{}{
		bson.D{{"title", "The Bluest Eye"}, {"author", "Toni Morrison"}},
		bson.D{{"title", "Sula"}, {"author", "Toni Morrison"}},
		bson.D{{"title", "Song of Solomon"}, {"author", "Toni Morrison"}},
	})
	return result, err
}, txnOptions)

If you require more control over your transactions, you can find an example showing how to manually create, commit, and end transactions in the full code example.

Additional Information

For more information about insert operations, see the Insert a Document fundamentals page.

For more information about write concerns, see the Modify Execution of CRUD Operations fundamentals page.

For an additional example using sessions and transactions with the Go driver, see the developer blog post on Multi-Document ACID Transactions.

API Documentation

To learn more about any of the types or methods discussed in this guide, see the following API Documentation:

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