secondary-adapter-repositories-deisgn-pattern.md

The design pattern for repositories adapters

Three different approaches to handling transactions across multiple repositories let's example business context in Order and Document

• Abstract Repository Combining Two/Multiple Repositories
• Transactor Repository (TransactorRepo)
• Transaction at the Repository Level (BeginTransaction Method) Let's explore the pros and cons of each, and I'll provide guidance on which might be the most suitable...

Approach 1: Abstract Repository Combining Two/Multiple Repositories (OrderDocumentRepo)

In this approach, you create an OrderDocumentRepo that combines both the OrderRepo and DocumentRepo into a single abstract repository, managing the transaction within this repository.

Pros:

• Single Responsibility: Encapsulates the entire transaction logic related to both orders and documents within a single repository, making it easy to manage.
• Consistency: Ensures that both order and document operations are tightly coupled within the same transaction scope, reducing the risk of partial failures.

Cons:

• Complexity: The repository becomes more complex as it handles more than one entity, potentially leading to a violation of the Single Responsibility Principle. Tight Coupling: Tightly couples OrderRepo and DocumentRepo, making it harder to reuse or test them independently.
• Scalability: If more repositories need to be added to the transaction, the OrderDocumentRepo would have to be modified, reducing flexibility.

Best Practice:

• This approach is suitable when the operations on orders and documents are always tied together and never operate independently.
• It can be useful when you need to ensure consistency between two repositories that are closely related and where changes are always made in tandem.

Approach 2: Transactor Repository (TransactorRepo)

In this approach, you define a TransactorRepo that provides a transaction context that can be passed to multiple repositories. The transaction is managed at the service level.

Pros:

• Loose Coupling: Keeps repositories independent from each other. The transaction management is handled separately, allowing repositories to remain focused on their own responsibilities.
• Flexibility: Easily extendable to support more repositories without modifying existing ones. Testability: Easier to test individual repositories independently, as they don't depend on each other.

Cons:

• Complexity: Slightly more complex as it requires managing transaction context explicitly in the service layer.
• Potential for Misuse: Requires careful management of transaction context to ensure it's passed correctly between repositories, which can be error-prone.

Best Practice:

• This approach is a good fit for a Hexagonal Architecture as it aligns well with dependency injection and separation of concerns. It allows you to inject the TransactorRepo into your service layer, making it flexible and scalable.
• It’s suitable for more complex systems where multiple repositories need to be part of a transaction but should remain loosely coupled.

Approach 3: Transaction at the Repository Level (BeginTransaction Method)

Here, each repository has its own BeginTransaction method, and the service manages the transaction by passing the transaction context to the repositories.

Pros:

• Granularity: Allows fine-grained control over transactions, enabling different repositories to manage their own transactions.
• Direct Control: Gives the service layer direct control over the transaction process, which can be useful in certain scenarios.

Cons:

• Code Duplication: Each repository needs to implement its own transaction management logic, leading to potential code duplication.
• Complexity: Increases the complexity of the service layer, as it must coordinate transaction management across multiple repositories. Risk of Inconsistency: Higher risk of inconsistencies if the transaction context is not managed properly across repositories.

Best Practice:

This approach is less common in Hexagonal Architecture because it mixes concerns and adds complexity. It's usually better to centralize transaction management rather than spreading it across repositories. Suitable only in cases where each repository truly needs its own independent transaction management.

Recommendation

Because this is the hexagonal architecture tutorial we will use the Approach 2 because of this below ...

Given your use of Hexagonal Architecture and dependency injection, Approach 2 (Transactor Repository) is generally the best practice:

• Decoupling: It keeps your repositories focused on their primary responsibilities without adding the burden of transaction management.
• Flexibility and Scalability: The transaction logic is centralized, making it easier to manage and extend to additional repositories if needed.
• Ease of Testing: By isolating transaction logic, you can more easily test your repositories and service logic independently.

This approach aligns well with the principles of Hexagonal Architecture, where the business logic (services) is kept separate from infrastructure concerns (like database transactions), and dependencies are injected where needed.

In summary, Approach 2 offers the right balance of flexibility, maintainability, and scalability, making it the most suitable choice for your scenario.