JPA之JPQL基础查询

@NamedQuery(name="test_jpql",query="SELECT t FROM TestJPQL t")
@Entity
@Table(name="TEST_JPQL")
public class TestJPQL {

    private Integer id;
    private String name;
    private String address;

    public TestJPQL(String name, String address) {
        super();
        this.name = name;
        this.address = address;
    }

    public TestJPQL() {
        super();
    }

    @Id
    @GeneratedValue
    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "TestJPQL [id=" + id + ", name=" + name + ", address=" + address + "]";
    }
}

createQuery查询基础

Query createQuery = entityManager.createQuery("SELECT t FROM TestJPQL t");

@SuppressWarnings("unchecked")
List<TestJPQL> resultList = createQuery.getResultList();
System.out.println(resultList);

代码中通过对象TestJPQL查询数据，调用getResultList返回一个List结果集

createQuery之new对象代码

Query createQuery = entityManager.createQuery("SELECT new TestJPQL(t.name,t.address) FROM TestJPQL t");

@SuppressWarnings("unchecked")
List<TestJPQL> resultList = createQuery.getResultList();
System.out.println(resultList);

通过在语句中new一个对象，将对应元素以对应参数传入查询。注意: 此时需要对实体类添加对应的有参构造器和和无参构造器。

createNamedQuery代码

Query createQuery = entityManager.createNamedQuery("test_jpql");

@SuppressWarnings("unchecked")
List<TestJPQL> resultList = createQuery.getResultList();
System.out.println(resultList);

在实体类需要添加@NamedQuery注解，name为createNamedQuery方法传入的参数，query为JPQL语句，可以有select部分，也没有没有。

createNativeQuery

Query createQuery = entityManager.createNativeQuery("SELECT id FROM test_jpql WHERE id = ? ");
createQuery.setParameter(1, 1);
Object singleResult = createQuery.getSingleResult();
System.out.println(singleResult);

通过createNativeQuery方法，传入SQL查询。且只能返回一个元素[即只能查询指定行的某列数据],
所以通过getSingleResult查询出对应列的数据。

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