Entity Manager

Entity Manager:

⚫ It is from data-jpa.

Add Entity to Database

public void persist(Object entity);

@Override
@Transactional //Handles transaction management
public void save(Student theStudent) {
    // if id=0 then save/insert else error
    entityManager.persist(theStudent); //Save theJava object
}

public <T> T merge(T entity);

@Override
@Transactional //Handles transaction management
public void save(Student theStudent) {
    // if id=0, then save/insert else update
    entityManager.merge(theStudent); //Save theJava object
}

Find Entity by Id

public <T> T find(Class<T> entityClass, Object primaryKey);

@Override //No need to add @Transactional since we are doing a query
public Student findById(Integer id) {
    return entityManager.find(Student.class, id); //If not found, returns null
}

Find All Entities

public <T> TypedQuery<T> createQuery(String qlString, Class<T> resultClass);

@Override
public List<Student> findAll() {
    //
    // create query
    //

    // Name of JPA Entity … the class name

    // this is NOT the name of the database table
    // All JPQL syntax is based on
    // entity name and entity fields
    TypedQuery<Student> theQuery = entityManager.createQuery("FROM Student", Student.class);

    // return query results
    return theQuery.getResultList();
}

Find Entities Based On Condition

public <T> TypedQuery<T> createQuery(String qlString, Class<T> resultClass);

@Override
public List<Student> findByLastName(String theLastName) {
    // create query
    TypedQuery<Student> theQuery = entityManager.createQuery(
                                    "FROM Student WHERE lastName=:theData", Student.class);

    // set query parameters
    theQuery.setParameter("theData", theLastName);

    // return query results
    return theQuery.getResultList();
}

Update Entity

public <T> T merge(T entity);

@Override
@Transactional //Add @Transactional since we are performing an update
public void update(Student theStudent) {

    entityManager.merge(theStudent);
}

Delete Entity

public void remove(Object entity);

@Override
@Transactional //Add @Transactional since we are performing a delete
public void delete(Integer id) {

    // retrieve the student
    Student theStudent = entityManager.find(Student.class, id);

    // delete the student
    entityManager.remove(theStudent);
}

Delete All Entities

public Query createQuery(String qlString);

@Override
@Transactional //Add @Transactional since we are performing a delete
public int deleteAll() {

    int numRowsDeleted = entityManager.createQuery("DELETE FROM Student").executeUpdate();

    return numRowsDeleted;
}