What is the significance of the @Transactional(propagation = Propagation.REQUIRED) annotation?

Table of Contents

• Introduction
  • 1. What is Transaction Propagation in Spring?
  • 2. How Does **Propagation.REQUIRED** Work?
    • Example 1: Using @Transactional(propagation = Propagation.REQUIRED) with Method Calls
  • 3. When to Use **Propagation.REQUIRED**
    • Practical Use Case: Managing User Registration
  • 4. Benefits of Using **Propagation.REQUIRED**
  • 5. When Not to Use **Propagation.REQUIRED**
• Conclusion

Introduction

In Spring, the @Transactional annotation is used to manage transactions declaratively. One of the key attributes of the @Transactional annotation is propagation, which controls how transactions are handled when a method that is already part of a transaction calls another transactional method. The default behavior of the @Transactional annotation is **Propagation.REQUIRED**, and understanding this propagation type is crucial for correctly managing transactional behavior in your application.

In this article, we'll explore the significance of the @Transactional(propagation = Propagation.REQUIRED) annotation, how it works, and when to use it effectively in your Spring-based application.

1. What is Transaction Propagation in Spring?

Transaction propagation refers to the behavior of transactions when one method, already part of a transaction, calls another method that is also transactional. The propagation setting controls whether the new method should join the existing transaction or start a new one.

Spring provides several propagation types, but **Propagation.REQUIRED** is the most commonly used one. Here are the main propagation types in Spring:

• **Propagation.REQUIRED** (default): Join the existing transaction if one exists; otherwise, start a new transaction.
• **Propagation.REQUIRES_NEW**: Start a new transaction, suspending the current one if it exists.
• **Propagation.NEVER**: Ensure that no transaction exists; if one does, throw an exception.
• **Propagation.MANDATORY**: Ensure that an existing transaction is already active; if not, throw an exception.
• **Propagation.SUPPORTS**: Join the existing transaction if one exists; otherwise, execute non-transactionally.
• **Propagation.NOT_SUPPORTED**: Suspend the existing transaction if one exists; execute non-transactionally.
• **Propagation.NESTED**: Execute within a nested transaction if an existing transaction exists; otherwise, behave like Propagation.REQUIRED.

2. How Does **Propagation.REQUIRED** Work?

**Propagation.REQUIRED** is the default propagation behavior of the @Transactional annotation. It means that if a method annotated with @Transactional(propagation = Propagation.REQUIRED) is called:

• If there is an existing transaction: The current method will join the existing transaction. This ensures that the transactional context is shared, which is ideal when multiple operations need to be part of a single unit of work.
• If there is no existing transaction: The method will start a new transaction. If no transaction is already in progress, Spring will begin a new one for the method call.

Example 1: Using @Transactional(propagation = Propagation.REQUIRED) with Method Calls

Consider the following example where two methods are annotated with @Transactional(propagation = Propagation.REQUIRED):

• When createUser() is called, if there is an existing transaction, saveUserToDatabase() will join that transaction. If not, Spring will create a new transaction for createUser().
• Both methods will either commit or roll back together based on the outcome of the operations inside both methods.

3. When to Use **Propagation.REQUIRED**

The default **Propagation.REQUIRED** is suitable for the majority of use cases in transactional applications. It should be used when you want a method to either:

• Join an existing transaction if one is active, or
• Start a new transaction if no transaction exists.

This ensures that methods are grouped together under one transaction, preserving the consistency of operations that need to be atomic (i.e., either all succeed or all fail).

Practical Use Case: Managing User Registration

Suppose you are building a user registration system, where user details are saved to a database and an email is sent after the user is registered. Both the database insert and the email sending should be part of the same transaction. If the database insert succeeds but the email fails, the database changes should be rolled back, and vice versa. Here's how Propagation.REQUIRED can be used to ensure that both actions are part of a single transaction:

In this case:

• Both saveUserToDatabase() and sendWelcomeEmail() will either be committed or rolled back together. If sending the email fails, the database operation will be rolled back due to the default Propagation.REQUIRED.

4. Benefits of Using **Propagation.REQUIRED**

• Simplicity: As the default propagation type, Propagation.REQUIRED is simple and intuitive for most use cases. It allows you to work with transactional methods without worrying about managing individual transaction boundaries.
• Transaction Consistency: It ensures that related operations (such as saving data to a database and updating related records) are treated as a single unit of work, maintaining the consistency of your application.
• Flexibility: You can safely use @Transactional(propagation = Propagation.REQUIRED) in multiple layers of your application (service, repository) without worrying about transaction management at each level.

5. When Not to Use **Propagation.REQUIRED**

While Propagation.REQUIRED is suitable for most cases, there are situations where other propagation behaviors may be more appropriate:

• When you need a new transaction: If you want a method to always start a new transaction (for example, when the method must execute independently of any existing transaction), use Propagation.REQUIRES_NEW.
• When no transaction is required: If you want a method to execute without a transaction, use Propagation.NOT_SUPPORTED.

Conclusion

The **@Transactional(propagation = Propagation.REQUIRED)** annotation is one of the most commonly used propagation settings in Spring. It ensures that if a transaction is already in progress, the current method will join that transaction; if not, a new transaction will be started. This default behavior helps in managing database operations as atomic units, simplifying transaction management in Spring applications. By using Propagation.REQUIRED, developers can easily ensure that related database operations are either fully committed or rolled back together, maintaining data consistency and integrity.