hibernate-jpa-api.jar中的@Transien

1.标签描述：

package javax.persistence;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Specifies that the property or field is not persistent. It is used
 * to annotate a property or field of an entity class, mapped
 * superclass, or embeddable class.
 *
 * <pre>
 *    Example:
 *
 *    &#064;Entity
 *    public class Employee {
 *        &#064;Id int id;
 *        &#064;Transient User currentUser;
 *        ...
 *    }
 * </pre>
 *
 * @since Java Persistence 1.0
 */
@Target({ METHOD, FIELD })
@Retention(RUNTIME)
public @interface Transient {
}

核心点：这个标签是用来指定属性或字段，是瞬时状态，不持久化到数据库中。

2.标签放置位置：亲测只有放置到属性的GET方法上，才会起作用!

@Entity
public class Books {
    private Integer id;
    private String name;
    private String author;
    private Integer price;
    private String description;
    private Date createTime;
    private Date updateTime;

    private String newParameter;


    @Transient
    public String getNewParameter() {
        return newParameter;
    }

    public void setNewParameter(String newParameter) {
        this.newParameter = newParameter;
    }
...

控制台Hibernate底层执行的SQL语句：可以看到在String newParameter;对应的GET方法上加上@Transient标签，插入SQL语句将自动排除这个字段。

Hibernate: 
    insert 
    into
        books
        (author, create_time, description, name, price, update_time) 
    values
        (?, ?, ?, ?, ?, ?)
{"description":"好好学习，承担医学传承","id":21,"name":"神农本草经"}