JPA之联合主键[复合主键]

ゝ一纸荒年。 2022-05-20 05:34 267阅读 0赞

`方法1:通过@IdClass注解指定复合主键对象`

//复合主键对象:
    public class IdClass implements Serializable{ 
        private Integer a_id;
        private Integer b_id;
        public Integer getA_id() {
            return a_id;
        }
        public void setA_id(Integer a_id) {
            this.a_id = a_id;
        }
        public Integer getB_id() {
            return b_id;
        }
        public void setB_id(Integer b_id) {
            this.b_id = b_id;
        }
    }
    
    
    
    //实体类对象
    @Entity
    @Table(name="A")
    @IdClass(com.ieb.bean.IdClass.class)
    public class A implements Serializable { 
        private Integer a_id;
        private String name;
        private Integer b_id;
    
        @Id
        public Integer getB_id() {
            return b_id;
        }
        public void setB_id(Integer b_id) {
            this.b_id = b_id;
        }
        @Id
        public Integer getA_id() {
            return a_id;
        }
        public void setA_id(Integer a_id) {
            this.a_id = a_id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + ((a_id == null) ? 0 : a_id.hashCode());
            result = prime * result + ((b_id == null) ? 0 : b_id.hashCode());
            result = prime * result + ((name == null) ? 0 : name.hashCode());
            return result;
        }
        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            A other = (A) obj;
            if (a_id == null) {
                if (other.a_id != null)
                    return false;
            } else if (!a_id.equals(other.a_id))
                return false;
            if (b_id == null) {
                if (other.b_id != null)
                    return false;
            } else if (!b_id.equals(other.b_id))
                return false;
            if (name == null) {
                if (other.name != null)
                    return false;
            } else if (!name.equals(other.name))
                return false;
            return true;
        }
    }

**`复合主键对象必须要序列化，且对象需要有一个空构造器[默认存在，如果加了有参构造则需要手动添加无参构造器]。实体类对象可以不需要重写hashCode和Equals方法，也可以不序列化[最好序列化]。@IdClass注解指定对应复合主键类[.class]`**

`方法2:通过通过复合主键对象 + @Embeddable 和实体对象 + @EmbeddedId注解：`

//主键类
    @Embeddable
    public class PrimaryKey implements Serializable{ 
        private Integer a_id;
        private Integer b_id;
        public Integer getA_id() {
            return a_id;
        }
        public void setA_id(Integer a_id) {
            this.a_id = a_id;
        }
        public Integer getB_id() {
            return b_id;
        }
        public void setB_id(Integer b_id) {
            this.b_id = b_id;
        }
    }
    
    //实体类
    @Entity
    @Table(name="A")
    public class A{ 
        @EmbeddedId
        private PrimaryKey idCLass;
    
        public PrimaryKey getIdCLass() {
            return idCLass;
        }
        public void setIdCLass(PrimaryKey idCLass) {
            this.idCLass = idCLass;
        }
        private String name;
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
    }