How to implement transaction processing in MongoDB through SQL statements?

How to implement transaction processing in MongoDB through SQL statements?

Abstract: As a non-relational database, MongoDB has always been known for its high performance and scalability. However, for applications that require transaction processing, MongoDB did not support transaction functionality in earlier versions. However, starting from MongoDB version 4.0, a feature called Multi-Document ACID Transactions has been introduced, which can use SQL statements to implement transaction processing. This article will introduce in detail how to implement transaction processing through SQL statements in MongoDB, and provide specific code examples.

1. Introduction to the use of SQL statements in MongoDB
   In MongoDB, SQL statements can be executed by using MongoDB's official driver or third-party tools. Most SQL statements are valid in MongoDB, but some SQL statements cannot be executed directly in MongoDB because MongoDB is a non-relational database and is somewhat different from traditional relational databases.
2. How to use SQL statements to implement transaction processing in MongoDB
   A transaction refers to a series of operations that are treated as a logical unit, either all of them are executed successfully, or none of them are executed. In MongoDB, we can use SQL statements to implement transaction processing. The specific steps are as follows:

2.1 Create a transaction
Before starting a transaction, you first need to create a session (session). This session will Will be used for subsequent transaction operations. The code example for creating a session is as follows:

var session = db.getMongo().startSession();

2.2 Starting a transaction
After creating a session, we can start a new transaction by executing the BEGIN TRANSACTION statement. The code example is as follows:

session.startTransaction();

2.3 Executing transaction operations
In a transaction, we can execute multiple SQL statements to implement business logic. For example, if we need to insert two records in a transaction, the code example is as follows:

session.getDatabase('test').users.insert({name: '张三', age: 25});
session.getDatabase('test').users.insert({name: '李四', age: 30});

2.4 Submit or rollback the transaction
After all transaction operations are executed, we can choose to commit or rollback the transaction . If all transaction operations are executed successfully, we can use the COMMIT statement to commit the transaction. The code example is as follows:

session.commitTransaction();

If an error or exception occurs during transaction execution, we can use the ROLLBACK statement to roll back the transaction. The code example is as follows:

session.abortTransaction();

2.5 Ending the transaction and session
After committing or rolling back the transaction, we can use the END TRANSACTION statement to end the transaction. At the same time, the session also needs to be ended. The code example is as follows:

session.endSession();

3. Example: Implement transaction processing of transfers in MongoDB
   The following is a simple example that demonstrates how to use SQL statements to implement transaction processing of transfers in MongoDB.

var session = db.getMongo().startSession();
session.startTransaction();

try {
  var fromAccount = session.getDatabase('bank').accounts.findOne({accountNumber: '123456'});
  var toAccount = session.getDatabase('bank').accounts.findOne({accountNumber: '654321'});

  var amount = 100;

  if (fromAccount.balance >= amount) {
    session.getDatabase('bank').accounts.updateOne({accountNumber: '123456'}, {$inc: {balance: -amount}});
    session.getDatabase('bank').accounts.updateOne({accountNumber: '654321'}, {$inc: {balance: amount}});
  } else {
    throw new Error('Insufficient balance');
  }

  session.commitTransaction();
} catch (error) {
  session.abortTransaction();
  print('Transaction failed: ' + error);
} finally {
  session.endSession();
}

In the above example, we first create a session and then start a new transaction. Afterwards, the account information is obtained based on the source account and target account of the transfer. If the balance of the source account is sufficient, the transfer operation is performed and the account balance is updated. Finally, the entire transfer process is completed by submitting the transaction.

Summary: Implementing transaction processing in MongoDB through SQL statements can make cross-document operations more convenient. Although MongoDB is a non-relational database, by introducing the Multi-Document ACID Transactions function, we can use SQL statements to implement transaction processing. In the code example, we use MongoDB's official driver to execute SQL statements, but other third-party tools can also be used to achieve this.

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