Hibernate about one-way, bidirectional Association mappings

"Hibernate" About one-way, bidirectional Association mappings

First we look at Hibernate's official explanation for one-to-one unidirectional association:

The one-way and one-way associations based on the foreign Key association are almost the same as the unidirectional many-to-one association. The only difference is a one-way off.

The Foreign key field in the union has a uniqueness constraint.

OK, then we can also understand that one-to-many is a special form of association, we know that hibernate is configured in two ways, namely, Annotations,XML two configuration mode!

Annotations One-way Association mappings

Person (User) and Social Security Number (card)

@Entity @table (name= "T_user") publicclass user {    private Integer ID;    private String name;    Private card card;         @OneToOne    @JoinColumn (name= "card_id", Unique=true)//name is the column name of the Custom Association foreign key public    card Getcard () {       Returncard ;    }    Publicvoid Setcard (card) {       this.card = card;    }    @Id    @GeneratedValue public    Integer getId () {       returnid;    }    Publicvoid setId (integerid) {       this.id = ID;    }         @Column (name= "name") public    String GetName () {       returnname;    }    Publicvoid SetName (stringname) {       this.name = name;    }

@Entity @table (name= "T_card") Publicclass card {    private Integer ID;    Private String num;         @Id    @GeneratedValue public    Integer getId () {       returnid;    }    Publicvoid setId (integerid) {       this.id = ID;    }    @Column (name= "card_id") public    String Getnum () {       returnnum;    }    Publicvoid Setnum (stringnum) {       this.num = num;    }}

XML One-Way Association

Person and the Group , a person can only be in a group

Publicclass Group {    private Integer ID;    private String name;    Public Integer getId () {       returnid;    }    Publicvoid setId (integerid) {       this.id = ID;    }    Public String GetName () {       returnname;    }    Publicvoid SetName (stringname) {       this.name = name;    }}

Publicclass person {    private Integer ID;    private String name;    Private Integer age;    Private group group;    Public Group Getgroup () {       returngroup;    }    Publicvoid Setgroup (groupgroup) {       this.group = group;    }    Public Integer getId () {       returnid;    }    Publicvoid setId (integerid) {       this.id = ID;    }    Public String GetName () {       return name;    }    public void SetName (Stringname) {       this.name = name;    }    Public Integer Getage () {       return age;    }    Publicvoid setage (Integer age) {       this.age = age;    }}

<?xml version= "1.0"? ><! DOCTYPE hibernate-mapping public     "-//hibernate/hibernate mapping DTD 3.0//en"    "http// Hibernate.sourceforge.net/hibernate-mapping-3.0.dtd ">

<?xml version= "1.0"? ><! DOCTYPE hibernate-mapping Public "-//hibernate/hibernate mapping DTD 3.0//en" "Http://hibernate.sourceforge.net/hib Ernate-mapping-3.0.dtd ">
Ok, here, everyone is a little puzzled, why our annotaions configuration is one-to-one and our XML configuration is Many-to-one?
Of course, the XML configuration is my reference to hibernate's documentation, because one on the other is a multi-pair special form,
But configuration Many-to-one gives us a hint that multiple numbers correspond to one person, so hibernate provides unique uniqueness to confirm this situation!

Annotations one-to-one bidirectional correlation mapping

User and the Card

@Entity @table (name= "T_user") publicclass user {    private Integer ID;    private String name;    Private card card;    @OneToOne    @JoinColumn (name= "card_id", Unique=true)//name is primarily a custom association foreign key column name public    card Getcard () {       Returncard;    }    Publicvoid Setcard (cardcard) {       this.card = card;    }    @Id    @GeneratedValue public    Integer getId () {       returnid;    }    Publicvoid setId (integerid) {       this.id = ID;    }    @Column (name= "name") public    String GetName () {       returnname;    }    Publicvoid SetName (stringname) {       this.name = name;    }}

@Entity @table (name= "T_card") Publicclass card {    private Integer ID;    Private String num;    private user user;         @OneToOne (mappedby= "card")//mappedby means to specify the card in user as the associated foreign key, otherwise the user and card will appear the foreign key public    user GetUser () {       Returnuser;    }    Publicvoid SetUser (useruser) {       this.user = user;    }    @Id    @GeneratedValue public    Integer getId () {       returnid;    }    Publicvoid setId (integerid) {       this.id = ID;    }    @Column (name= "card_id") public    String Getnum () {       returnnum;    }    Publicvoid Setnum (stringnum) {       this.num = num;    }}

Ok? So we can see that the configuration in Annotaions is Ont-to-one, so what are our configurations in XML? 
<?xml version= "1.0"? ><! DOCTYPE hibernate-mapping public     "-//hibernate/hibernate mapping DTD 3.0//en"    "http// Hibernate.sourceforge.net/hibernate-mapping-3.0.dtd ">

<?xml version= "1.0"? ><! DOCTYPE hibernate-mapping public     "-//hibernate/hibernate mapping DTD 3.0//en"    "http// Hibernate.sourceforge.net/hibernate-mapping-3.0.dtd ">

OK, to here a one-way correlation mapping is basically the case, essays, there are problems, please leave a message!






Hibernate about one-way, bidirectional Association mappings