Hibernate: CRUD Generic DAO

Question

My web application has got a lot of service tables/entities, such as payment_methods, tax_codes, province_codes, etc.

Each time

Answer 1

you can use Generic DAO as leverage for other Domain specific DAO classes. Suppose you have an Employee Domain class as:

  @Entity
  @Table(name="employee")
  public class Employee {

    @Id
    @Column(name="id")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    @Column(name="emp_name")
    private String empName;

    @Column(name="emp_designation")
    private String empDesignation;

    @Column(name="emp_salary")
    private Float empSalary;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    public String getEmpDesignation() {
        return empDesignation;
    }

    public void setEmpDesignation(String empDesignation) {
        this.empDesignation = empDesignation;
    }

    public Float getEmpSalary() {
        return empSalary;
    }

    public void setEmpSalary(Float empSalary) {
        this.empSalary = empSalary;
    }


}

then the required generic DAO would look something like this:

Generic DAO Interface:

 public interface GenericRepositoryInterface {

    public T save(T emp);
    public Boolean delete(T emp);
    public T edit(T emp);
    public T find(Long empId);
}

Generic DAO implementation:

@Repository
public class GenericRepositoryImplementation implements GenericRepositoryInterface {

protected EntityManager entityManager;
private Class type;

public GenericRepositoryImplementation() {
    // TODO Auto-generated constructor stub

}

public GenericRepositoryImplementation(Class type) {
    // TODO Auto-generated constructor stub

    this.type = type;
}

public EntityManager getEntityManager() {
    return entityManager;
}

@PersistenceContext
public void setEntityManager(EntityManager entityManager) {
    this.entityManager = entityManager;
}
@Override
public T save(T emp) {
    // TODO Auto-generated method stub
    entityManager.persist(emp);
    entityManager.flush();
    return emp;
}

@Override
public Boolean delete(T emp) {
    // TODO Auto-generated method stub
    try {
         entityManager.remove(emp);
    } catch (Exception ex) {
        return false;
    }
    return true;
}

@Override
public T edit(T emp) {
    // TODO Auto-generated method stub
    try{
       return entityManager.merge(emp);
    } catch(Exception ex) {
        return null;
    }
}

@Override
public T find(Long empId) {
    // TODO Auto-generated method stub
    return (T) entityManager.find(Employee.class, empId);
}
} 

This generic DAO class then needs to be extended by every Domain specific DAO class. The Domain specific DAO class may even implement another interface for operations that are not common in general. And prefer sending type information using constructor.