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 * * * (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 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;     } &nbSp;  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/HIBERNATE-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 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!





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Hibernate about one-way, bidirectional Association mappings