layout: page title: “repositories” permalink: /repositories

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Repositories 🏠

layer : domain 🔴 / infrastructure 🟢

Repository pattern is the way that DDD has to decouple domain and infrastructure in terms of entities.They are the entities persistance manager classes.

• First, in domain layer 🔴, you have to create an INTERFACE which does something (usually CRUD methods) but you only specify WHAT the repository does.

package com.workers.domain;

import java.util.ArrayList;
import org.springframework.stereotype.Service;
import com.incidences.domain.Incidence.IncidenceAssignation;

@Service // this annotation is important

public interface WorkerRepository {
  //just a few methods as demo
  
	public void save(Worker worker);
	public Worker searchById(WorkerId id);
	public ArrayList<String> getAllWorkers();
	public ArrayList<IncidenceAssignation>allAssignedIncidencesByWorker(WorkerId id);
	
}

• Later, in domain 🟢 layer, you have to implement the interface in order to tell the app HOW to accomplish the task of each method. Is in this layer where SQL commands, transactions, MongoDB… may appear. Nowhere else.

package com.workers.infrastructure;

import java.util.ArrayList;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.transaction.Transactional;
import org.springframework.stereotype.Repository;
import com.incidences.domain.IncidenceId;
import com.incidences.domain.Incidence.IncidenceAssignation;
import com.workers.domain.Worker;
import com.workers.domain.WorkerId;
import com.workers.domain.WorkerRepository;


@Repository //this annotation is needed

public class WorkerRepositoryMysqlImplementation implements WorkerRepository {
	
 
	@PersistenceContext  //this is used in order to avoid JPA and make the app less framework dependent, but I have also watched injected JPA examples.
    private EntityManager entityManager;
	
	
	@Override
	@Transactional // This annotation is necessary for saving methods
	public void save(Worker worker) {
		//this could be a sql statemnt
		 entityManager.persist(worker);
		 entityManager.close();
	}
  
  rest of methods

In my opinion, the most repository method influenced by business rules are searchs (e.g: search all entities following some criteria), but maybe a company just saves entities which “starts with R” or whatever. As I said this is only my experience. I’m sure there will be many different opinions.

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some interesting external links :

• microsoft - Repository pattern

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index

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