One-on-one

One-to-one primary key Association

1.XML configuration

• Must be bi-directional
• The primary key generation strategy of the associated party is a foreign key generation strategy
• The associated party one-to-one needs to set constrained= "true" constraint

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="Person" table="person">
        <id column="id" name="id">
           <generator class="native"/>
        </id>
        <property name="personName" column="person_name"/>
        <one-to-one name="card" cascade="all"/>
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="Card" table="card">
        <id column="id" name="id">
            <generator class="foreign">
                <param name="property">person</param>
            </generator>
        </id>
        <property name="cardNum" column="card_num"/>
        <one-to-one name="person" constrained="true"/>
    </class>
</hibernate-mapping>

2.Java Annotation Configuration

• The main control party uses @PrimaryKey Join Column
• The accused should add (mappedBy = card) in @OneToOne.

//Annotation-based configuration
@Entity
@Table(name = "person")
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "person_name")
    private String personName;

    //Sharing primary key associations using PrimaryKey Join Column
    @OneToOne(cascade = CascadeType.ALL)
    @PrimaryKeyJoinColumn
    private Card card;
  }

@Entity
@Table(name = "card")
public class Card {
    @Id
    @GenericGenerator(name = "generator",strategy = "foreign",
            parameters = @org.hibernate.annotations.Parameter(name = "property",value = "person"))
    @GeneratedValue(generator = "generator")
    private Integer id;

    @Column(name = "card_num")
    private String cardNum;


    //You must set OneToOne,mappedBy, as your attribute name in the other party
    @OneToOne(mappedBy = "card")
    private Person person;
  }

One-to-one foreign key Association

database structure

1.XML configuration

• Each primary key generation strategy has no foreign key constraints
• The main control party (the party with foreign keys) uses many-to-one and adds unique="true" constraints.
• The accused uses one-to-one and adds property-ref="passageContent"

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="Passage" table="passage">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="title" column="title"/>
        <many-to-one name="passageContent" column="content_id" class="PassageContent" unique="true"/>
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="PassageContent" table="passage_content">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="content" column="content"/>
        <one-to-one name="passage" class="Passage" property-ref="passageContent"/>
    </class>
</hibernate-mapping>

2.Java Annotation Configuration

• Unlike XML configuration, all of them use @OneToOne
• The main control party uses @JoinColumn (name = content_id)
• The accused uses @OneToOne (mappedBy = passageContent), which is equivalent to property-ref in XML and is a reverse declaration.

@Entity
@Table(name = "passage")
public class Passage {

    @Id
    @GeneratedValue
    private Integer id;
    private String title;

    @OneToOne
    @JoinColumn(name = "content_id")
    private PassageContent passageContent;
  }

@Entity
@Table(name = "passage_content")
public class PassageContent {

    @Id
    @GeneratedValue
    private Integer id;
    private String content;


    @OneToOne(mappedBy = "passageContent")
    private Passage passage;
  }

One-to-many Association

• Save one end before multiple ends
  database structure

  
  
  
  

  One-to-many Association
  
  

  1.XML configuration

• At one end of the set, the table and associated keys (i.e., table and key attributes) are specified, and relationship maintenance is abandoned.

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="Address" table="address">
        <id name="id" column="id">
            <generator class="native"/>
        </id>


        <property name="cityName" column="city_name"/>
        <property name="address" column="address"/>
        
        <many-to-one name="user" class="User" column="user_id" lazy="false" fetch="join"></many-to-one>
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="User" table="user">
        <cache usage="read-only"/>
        <id name="id" column="id">
            <generator class="native"/>
        </id>


        <property name="username" column="username"/>
        <set name="addressSet" table="address" cascade="delete" inverse="true">
            <key column="user_id"></key>
            <one-to-many class="Address"></one-to-many>
        </set>
    </class>
</hibernate-mapping>

2.Java Annotation Configuration

• Join Column is added to ManyToOne, and mappedBy is added to OneToMany.
• Cascade is added to one end if cascade operation is required

@Entity
@Table
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "city_name")
    private String cityName;
    private String address;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;
  }

@Entity
@Table
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    private String username;

    @OneToMany(mappedBy = "user")
    @Cascade(CascadeType.DELETE)
    private Set<Address> addressSet;
  }

Many-to-many Association

database structure

1.XML configuration

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="Student" table="student">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="studentName" column="student_name"/>

        <set name="teacherSet" table="student_teacher_real">
            <key column="student_id"></key>
            <many-to-many class="Teacher" column="teacher_id"/>
        </set>
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.kaishengit.pojo">
    <class name="Teacher" table="teacher">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="teacherName" column="teacher_name"/>

        <set name="studentSet" table="student_teacher_real" inverse="true">
            <key column="teacher_id"></key>
            <many-to-many class="Student" column="student_id"/>
        </set>
    </class>
</hibernate-mapping>

2.Java Annotation Configuration

@Entity
@Table
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;



    @Column(name = "student_name")
    private String studentName;

    public Integer getId() {
        return id;
    }

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

    @ManyToMany
    @JoinTable(name = "student_teacher_real",joinColumns = {@JoinColumn(name = "student_id")},inverseJoinColumns = {@JoinColumn(name = "teacher_id")})
    private Set<Teacher> teacherSet;
  }

@Entity
@Table
public class Teacher {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "teacher_name")
    private String teacherName;

    @ManyToMany(mappedBy = "teacherSet")
    private Set<Student> studentSet;
  }

Java Annotation Summary

• If it is a primary key association, then use @PrimaryKey JoinColumn, as long as it declares that @JoinColumn, @PrimaryKey JoinColumn, @JoinTable belongs to the main control, and foreign keys are usually stored in the main control, and the corresponding ones containing mappedBy are the accused.
• One-to-one associations, whether primary or foreign key associations, are OneToOne based on annotations

Summary of XML Configuration

• When one-to-one primary key Association occurs, because the primary key of the accused party is the foreign key of the accused party, constrained="true" constraint is required in the OneToOne tag of the accused party.
• The accused usually needs to set inverse="true" to abandon relationship maintenance.
• Labels like < one-to-many > < many-to-many > are placed inside the < set > collection