如何解决如何使用休眠条件连接 3 个表?
我有三张桌子。
- 父母
- parent_child_mapping
- 孩子
我想加入 3 个表并使用“CriteriaBuilder”和“Predicate”按子名称过滤。 我如何使用“CriteriaBuilder”和“Predicate”来实现以下 sql 查询。
SELECT p.parent_id
FROM parent p
JOIN parent_child_mapping pcmap on p.parent_id = pcmap.mapping_parent_id
JOIN child c on pcmap.mapping_child_id = c.child_id
WHERE c.child_name = 'abc'
父实体
@Entity
@Table(name = "parent")
public class Parent {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "parent_id")
private Long parentId;
....
@OneToMany(cascade = CascadeType.ALL,mappedBy = "mappingParentId")
private Collection<ParentChildMapping> parentChildMappingCollection;
}
父子映射实体
@Entity
@Table(name = "parent_child_mapping")
public class ParentChildMapping{
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "mapping_id")
private Long mappingId;
@JoinColumn(name = "mapping_child_id")
@ManyToOne(optional = false)
private ChildEntity mappingChildId;
@JoinColumn(name = "mapping_parent_id")
@ManyToOne(optional = false)
private ParentEntity mappingParentId;
}
子实体
@Data
@Entity
@Table(name = "child")
public class Child implements Serializable
{
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "child_id")
private Long childId;
@Basic(optional = false)
@NotNull
@Size(min = 1,max = 255)
@Column(name = "child_name")
private String childName;
}
解决方法
您只需为每个实体创建一个根并将条件添加到 where 子句中。像这样:
Root<Parent> parent = criteriaQuery.from(Parent.class);
Root<ParentChildMapping> mapping = criteriaQuery.from(ParentChildMapping.class);
Root<Child> child = criteriaQuery.from(Child.class);
criteriaQuery.select(parent.get("parentId"));
criteriaQuery.where(
criteriaBuilder.and(
criteriaBuilder.equal(parent.get("parentId"),mapping.get("mappingParentId")),criteriaBuilder.equal(child.get("childId"),mapping.get("mappingChildId")),criteriaBuilder.equal(child.get("childName"),"abc")
)
);
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