Annotation of Hibernate

When the project becomes relatively large, how to use the hbm. xml file to configure Hibernate entities becomes more complex. Here, Hibernate provides the Annotation method, which makes the Hibernate ing file easy to manage.

Here is a brief introduction to the Annotation of Hibernate.

@ Entity

Annotate objects. This annotation is required for any Hibernate ing object.

@ Table

Declare the data table mapped to the database. You can specify the table (talbe), directory (Catalog), and schema names for the object. This annotation is not required. If not, the system uses the default value (short class name of the object ).

@ Version

This annotation can be used to add optimistic lock support to the Entity Bean.

 

@ Id

Declare this attribute as the primary key. This attribute value can be created by itself, but it is recommended that it be generated by Hibernate.

@ GeneratedValue

Specifies the primary key generation policy. There are four values:

TABLE: use the TABLE to save the id value.

IDENTITY: identitycolumn

SEQUENCR: sequence

AUTO: Use the preceding three methods based on different databases.

@ Column

Declares the ing between this attribute and the database fields.

 @Column(nam=”category_name” length=20 Public      Return  } 

1. When POJO has attributes that do not need to be mapped, it must be modified with @ Transitent. This comment indicates that this attribute has no ing relationship with the table and is only a temporary attribute.

2. @ Lob annotation indicates that the attribute persists to the Blob or Clob type, depending on the attribute type.

 

One-to-Multiple Association

@ OneToMany (mappedBy = "person", cascade = CascadeType. ALL, fetch = FetchType. LAZY)

One-to-multiple Declaration

@ ManyToOne (cascade = CascadeType. REFRESH ,)

@ JoinColumn

Multiple-to-one declaration, declared as two-way Association

 

One-to-one Association

@ OneToOne (optional = true, cascade = CascadeType. ALL, mappedBy = "person ")
One-to-one association statement
@ OneToOne (optional = false, cascade = CascadeType. REFRESH)
@ JoinColumn (name = "Person_ID", referencedColumnName = "personid", unique = true)
Declared as bidirectional Association

 

Multi-to-Multi-Association

@ ManyToMany (mappedBy = "students ")
Multiple-to-Multiple Association Declaration.
@ ManyToMany (cascade = CascadeType. PERSIST, fetch = FetchType. LAZY)
@ JoinTable (name = "Teacher_Student ",
JoinColumns = {@ JoinColumn (name = "Teacher_ID", referencedColumnName = "teacherid ")},
InverseJoinColumns = {@ JoinColumn (name = "Student_ID", referencedColumnName = "studentid ")})

 

Instance:

There are two entities: Goods and Category. The two are many-to-one associations.

The Hibernate Annotation is as follows:

    @Table(name = "goods", catalog = "test"   Goods           serialVersionUID = 1L                                            @Column(name = "goods_id", unique = , nullable = , length = 20                                .goodsId =                      @ManyToOne(fetch = FetchType.LAZY,cascade=     @JoinColumn(name = "category_id"                                .category =       @Column(name = "goods_name", nullable = , length = 50                                .goodsName =   }

 

Category. java

  @Table(name = "category", catalog = "test"   Category           serialVersionUID = -1877960009126534682L                 Set<Goods> goodses =  HashSet<Goods>(0                             @Column(name = "category_id", unique = , length = 10                                .categoryId =       @Column(name = "category_name", length = 20                                .categoryName =                      @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "category"      Set<Goods>                   setGoodses(Set<Goods>         .goodses =   }