@Entity @Table注解

@Entity @Table注解

来源

Java Persistence API中定义了两个注解@Entity与@Table

@Entity表明这是一个实体类，要与数据库做orm映射，默认表的名字就是类名，表中的字段就是类中的属性。它的定义如下：其中name属性表示用JPQL语句时写的表的名字，如果没有在@Table注解中指定表名，这个名字也将作为表名映射到数据库

@Documented
@Target(TYPE)
@Retention(RUNTIME)
public @interface Entity {
 
	/**
	 * (Optional) The entity name. Defaults to the unqualified
	 * name of the entity class. This name is used to refer to the
	 * entity in queries. The name must not be a reserved literal
	 * in the Java Persistence query language.
	 */
	String name() default "";
}

@Table 就是改变某些默认的映射规则，如表名，schema等，可以添加索引和约束，看一下它的定义

@Target(TYPE)
@Retention(RUNTIME)
public @interface Table {
	/**
	 * (Optional) The name of the table.
	 * <p/>
	 * Defaults to the entity name.
	 */
	String name() default "";
 
	/**
	 * (Optional) The catalog of the table.
	 * <p/>
	 * Defaults to the default catalog.
	 */
	String catalog() default "";
 
	/**
	 * (Optional) The schema of the table.
	 * <p/>
	 * Defaults to the default schema for user.
	 */
	String schema() default "";
 
	/**
	 * (Optional) Unique constraints that are to be placed on
	 * the table. These are only used if table generation is in
	 * effect. These constraints apply in addition to any constraints
	 * specified by the <code>Column</code> and <code>JoinColumn</code>
	 * annotations and constraints entailed by primary key mappings.
	 * <p/>
	 * Defaults to no additional constraints.
	 */
	UniqueConstraint[] uniqueConstraints() default { };
 
	/**
	 * (Optional) Indexes for the table. These are only used if table generation is in effect.  Defaults to no
	 * additional indexes.
	 *
	 * @return The indexes
	 */
	Index[] indexes() default {};
}

name: 用来指定要映射的表名

catalog: 指定table数据库中的路径，这里指数据库名

schema: 映射到哪个schema，用户名

uniqueConstraints： 可以创建单个字段或者联合的唯一约束，只有在创建表成功时才执行

indexes：索引，可以指定联合索引，也是只有表生成成功才有效

我的实体类代码，（只为了演示注解效果，在表结构设计上是非常不规范的，没有实际意义）

package com.xhx.springboot.entity;
 
import javax.persistence.*;
 
/**
 * @author xuhaixing
 * @date 2018/4/28 10:29
 */
@Entity(name = "Acc")
@Table(name = "account", //表名称
        catalog = "mytest2",   //数据库名
        schema = "xuhaixing",  //用户名
        uniqueConstraints = {   //联合或者单个字段 唯一约束
        @UniqueConstraint(columnNames = {"name","money"}), @UniqueConstraint(columnNames = {"name"})
        },
        indexes = {
        @Index(columnList = "name,version")
        }
        )
public class Account {
    @Id
    private int id;
    private String name;
    private Double money;
    @Version
    private int version;
 
 
    public int getVersion() {
        return version;
    }
 
    public void setVersion(int version) {
        this.version = version;
    }
 
    public int getId() {
        return id;
    }
 
    public void setId(int id) {
        this.id = id;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Double getMoney() {
        return money;
    }
 
    public void setMoney(Double money) {
        this.money = money;
    }
}
程序启动过程中执行的sql语句：

Hibernate: create table mytest2.account (id integer not null, money double precision, name varchar(255), version integer not null, primary key (id)) engine=MyISAM
Hibernate: create index IDXpdrwpyis5o4yn1f3n52oc756e on mytest2.account (name, version)
Hibernate: alter table mytest2.account drop index UKdqfeeghd5jfgxqfxae9urq0em
Hibernate: alter table mytest2.account add constraint UKdqfeeghd5jfgxqfxae9urq0em unique (name, money)
Hibernate: alter table mytest2.account drop index UKbb9lrmwswqvhcy1y430ki00ir
Hibernate: alter table mytest2.account add constraint UKbb9lrmwswqvhcy1y430ki00ir unique (name)
 

UniqueConstraint的源码如下，可以用name指定约束的名字

@Target({ })
@Retention(RUNTIME)
public @interface UniqueConstraint {
	/**
	 * (Optional) Constraint name.  A provider-chosen name will be chosen
	 * if a name is not specified.
	 *
	 * @since Java Persistence 2.0
	 */
	String name() default "";
 
	/**
	 * (Required) An array of the column names that make up the constraint.
	 */
	String[] columnNames();
}

Index注解源码如下，还可以用name指定索引的名字

@Target({}) @Retention(RUNTIME)
public @interface Index {
	/**
	 * (Optional) The name of the index.  Defaults to a provider-generated value.
	 *
	 * @return The index name
	 */
	String name() default "";
 
	/**
	 * (Required) The names of the columns to be included in the index.
	 *
	 * @return The names of the columns making up the index
	 */
	String columnList();
 
	/**
	 * (Optional) Whether the index is unique.  Default is false.
	 *
	 * @return Is the index unique?
	 */
	boolean unique() default false;
}

我的dao层代码：

package com.xhx.springboot.dao;
 
import com.xhx.springboot.entity.Account;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
 
/**
 * @author xuhaixing
 * @date 2018/5/2 11:19
 */
@Repository
public interface AccountDao extends JpaRepository<Account, Integer> {
 
 
    @Modifying
    @Query("update Acc set name=:name, money=:money where id=:id")
    int updateAccount(@Param("id") int id,@Param("name") String name, @Param("money") double money);
 
 
    @Modifying  //通知jpa这是一个update或者delete操作，jpql不支持insert操作
    @Query("update Acc set name=:name, money=:money,version=:version+1 where id=:id and version=:version")
    int updateAccountByVersion(@Param("id") int id,@Param("name") String name, @Param("money") double money,@Param("version") int version);
 
    @Query(value = "select count(*) from account",nativeQuery = true)//使用原生sql进行查询
    long selectCount();
 
}
 

至此，@Table和@Entity的注解所有属性就讲解完了