OneToOne 、OneToMany 、 ManyToMany

OneToOne   OneToMany   ManyToMany

@ManyToOne   默认fetch=FetchType.enger
@OneToMany   默认fetch=FetchType.Lazy

重要：
双向关系：一定分别在两个类里面设“双向关联”即（假如dish和Sort双向关系：sort里面设：OneToMany（mappedBy="sort"）    dish里面设：@ManyToOne）
双向关联:一定要设   XXToXX(mappedBy="")  便于表之间数据一致



一、联合主键

@Entity
class Customer {
   @EmbeddedId CustomerId id;
   boolean preferredCustomer;
}

@Embeddable
class CustomerId implements Serializable {
   @OneToOne
   @JoinColumns({
      @JoinColumn(name="userfirstname_fk", referencedColumnName="firstName"),
      @JoinColumn(name="userlastname_fk", referencedColumnName="lastName")
   }) 
   User user;
   String customerNumber;

   //implements equals and hashCode
}

@Entity 
class User {
   @EmbeddedId UserId id;
   Integer age;
}

@Embeddable
class UserId implements Serializable {
   String firstName;
   String lastName;


   //implements equals and hashCode
}

<class name="Customer">
   <composite-id name="id" class="CustomerId">
      <key-property name="firstName" column="userfirstname_fk"/>
      <key-property name="lastName" column="userfirstname_fk"/>
      <key-property name="customerNumber"/>
   </composite-id>

   <property name="preferredCustomer"/>

   <many-to-one name="user">
      <column name="userfirstname_fk" updatable="false" insertable="false"/>
      <column name="userlastname_fk" updatable="false" insertable="false"/>
   </many-to-one>
</class>

<class name="User">
   <composite-id name="id" class="UserId">
      <key-property name="firstName"/>
      <key-property name="lastName"/>
   </composite-id>

   <property name="age"/>
</class>

二、one-To-many单向关联

public class Parent {
    @Id
    @GeneratedValue
    private long id;

    @OneToMany
    private Set<Child> children;

    // getter/setter
    ...
}


public class Child {
   @Id
   @GeneratedValue
   private long id;
   private String name;

   
   // getter/setter
   ...
}

<hibernate-mapping>

    <class name="Parent">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <set name="children">
            <key column="parent_id"/>
            <one-to-many class="Child"/>
        </set>
    </class>

    <class name="Child">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <property name="name"/>
    </class>

</hibernate-mapping>

create table parent ( id bigint not null primary key )
create table child ( id bigint not null primary key, name varchar(255), parent_id bigint )
alter table child add constraint childfk0 (parent_id) references parent

三、one-To-many 双向关联如果父亲是必须的，那么就可以使用双向 one-to-many 的关联了

public class Parent {
    @Id
    @GeneratedValue
    private long id;

    @OneToMany(mappedBy="parent")
    private Set<Child> children;

    // getter/setter
    ...
}


public class Child {
   @Id
   @GeneratedValue
   private long id;

   private String name;
 
   @ManyToOne
   @JoinColumn(name="parent_id")//与上面的OneToMany(mappedBy="parent")对应
   private Parent parent;

   
   // getter/setter
   ...
}

<hibernate-mapping>

    <class name="Parent">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <set name="children" inverse="true">
            <key column="parent_id"/>
            <one-to-many class="Child"/>
        </set>
    </class>

    <class name="Child">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <property name="name"/>
        <many-to-one name="parent" class="Parent" column="parent_id" not-null="true"/>
    </class>

</hibernate-mapping>

create table parent ( id bigint not null primary key )
create table child ( id bigint not null
                     primary key,
                     name varchar(255),
                     parent_id bigint not null )
alter table child add constraint childfk0 (parent_id) references parent

四、one-To-many单向   外键不为空Not Null

public class Parent {
    @Id
    @GeneratedValue
    private long id;

    @OneToMany(optional=false)
    private Set<Child> children;

    // getter/setter
    ...
}


public class Child {
   @Id
   @GeneratedValue
   private long id;
   private String name;

   
   // getter/setter
   ...
}

hibernate-mapping>

    <class name="Parent">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <set name="children">
            <key column="parent_id" not-null="true"/>
            <one-to-many class="Child"/>
        </set>
    </class>

    <class name="Child">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <property name="name"/>
    </class>

</hibernate-mapping>

五、many-To-many

public class Parent {
    @Id
    @GeneratedValue
    private long id;

    @ManyToMany
    private Set<Child> children;

    // getter/setter
    ...
}


public class Child {
   @Id
   @GeneratedValue
   private long id;

   private String name;

   
   // getter/setter
   ...
}

<hibernate-mapping>

    <class name="Parent">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <set name="children" table="childset">
            <key column="parent_id"/>
            <many-to-many class="Child" column="child_id"/>
        </set>
    </class>

    <class name="Child">
        <id name="id">
            <generator class="sequence"/>
        </id>
        <property name="name"/>
    </class>

</hibernate-mapping>

create table parent ( id bigint not null primary key )
create table child ( id bigint not null primary key, name varchar(255) )
create table childset ( parent_id bigint not null,
                        child_id bigint not null,
                        primary key ( parent_id, child_id ) )
alter table childset add constraint childsetfk0 (parent_id) references parent
alter table childset add constraint childsetfk1 (child_id) references child