## Why is this an issue?

Transactional methods have a propagation type parameter in the @Transaction annotation that specifies the requirements about the transactional context in which the method can be called and how it creates, appends, or suspends an ongoing transaction.

When an instance that contains transactional methods is injected, Spring uses proxy objects to wrap these methods with the actual transaction code.

However, if a transactional method is called from another method in the same class, the `this` argument is used as the receiver instance instead of the injected proxy object, which bypasses the wrapper code. This results in specific transitions from one transactional method to another, which are not allowed:

From | To
--- | ---
non-`@Transactional` | MANDATORY, NESTED, REQUIRED, REQUIRES_NEW
MANDATORY | NESTED, NEVER, NOT_SUPPORTED, REQUIRES_NEW
NESTED | NESTED, NEVER, NOT_SUPPORTED, REQUIRES_NEW
NEVER | MANDATORY, NESTED, REQUIRED, REQUIRES_NEW
NOT_SUPPORTED | MANDATORY, NESTED, REQUIRED, REQUIRES_NEW
REQUIRED or `@Transactional` | NESTED, NEVER, NOT_SUPPORTED, REQUIRES_NEW
REQUIRES_NEW | NESTED, NEVER, NOT_SUPPORTED, REQUIRES_NEW
SUPPORTS | MANDATORY, NESTED, NEVER, NOT_SUPPORTED, REQUIRED, REQUIRES_NEW

## How to fix it

Change the corresponding functions into a compatible propagation type.

### Code examples

#### Noncompliant code example

    public void doTheThing() {
      // ...
      actuallyDoTheThing(); // Noncompliant, call from non-transactional to transactional
    }

    @Transactional
    public void actuallyDoTheThing() {
      // ...
    }

#### Compliant solution

    @Transactional
    public void doTheThing() {
      // ...
      actuallyDoTheThing(); // Compliant
    }

    @Transactional
    public void actuallyDoTheThing() {
      // ...
    }

#### Noncompliant code example

    @Transactional
    public void doTheThing() {
      // ...
      actuallyDoTheThing(); // Noncompliant, call from REQUIRED to REQUIRES_NEW
    }

    @Transactional(propagation = Propagation.REQUIRES_NEW)
    public void actuallyDoTheThing() {
      // ...
    }

#### Compliant solution

    @Transactional
    public void doTheThing() {
      // ...
      actuallyDoTheThing(); // Compliant, call from REQUIRED to MANDATORY
    }

    @Transactional(propagation = Propagation.MANDATORY)
    public void actuallyDoTheThing() {
      // ...
    }

## Resources

- Spring Framework 6 API: Enum Class propagation
- Spring Framework 6 API: Annotation Interface Transactional
- Spring 6 Documentation: Transaction Propagation

### Articles & blog posts

- Baeldung: Transaction Propagation and Isolation in Spring @Transactional
- DZone: Spring Transaction Propagation in a Nutshell