hibernate dynamic-insert 和 dynamic-update使用

默认情况下，在hibernate启动的时候，会为每个实体类生成简单的读取，删除，更新，创建语句，它是怎么生成更新的呢，它怎么知道更新的列，生成更新所有列的sql语句，如果值没有修改，则被设置为它的旧值，如果表的列比较多，即使只更新了一个列，也会生成很长的sql语句，必须关闭启动时生成sql语句，hibernate提供了dynamic-insert和dynamic-update属性，用来关闭生成sql语句，看下面例子。
持久化类

  package com.own.model;

import java.io.Serializable;

public class Goods implements Serializable {
	
	
	private static final long serialVersionUID = 1L;
	private Integer id;
	private  String goodsName;
	private Double price;
	private String goodsDescription;	
	
	public Goods(){}
	
	public Integer getId() {
		return id;
	}
	
	public void setId(Integer id) {
		this.id = id;
	}
	public String getGoodsName() {
		return goodsName;
	}
	public void setGoodsName(String goodsName) {
		this.goodsName = goodsName;
	}
	public Double getPrice() {
		return price;
	}
	public void setPrice(Double price) {
		this.price = price;
	}
	public String getGoodsDescription() {
		return goodsDescription;
	}
	public void setGoodsDescription(String goodsDescription) {
		this.goodsDescription = goodsDescription;
	}

	
	@Override
	public boolean equals(Object o) {
		
		if(o == null || o.getClass() != this.getClass()){
			return false;
		}
		
		if(o == this){
			return true;
		}
		
		Goods goods = (Goods) o;
		
		if(id == null ? goods.id == null : this.id.equals(goods.id)){
			return true;
		}
		
		
		return false;
	}
	
	@Override
	public int hashCode() {
		return this.id.hashCode()  ;
	}
	
}

  <?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
      "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
          "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping >

        <class name="com.own.model.Goods"  table="goods" dynamic-insert="false" dynamic-update="false"     >
          
           <id name="id"  column="goods_id" >
              <generator class="native"></generator>
           </id>
            <property name="price"  column="goods_price" type="double"  ></property>  
            <property name="goodsName"  column="goods_name" type="string"  ></property>  
            <property name="goodsDescription"  column="goods_description" type="string"  ></property>  
            
            
        </class>
  
  
 
      
</hibernate-mapping>
   

调用hibernate的保存和更新方法，会生成如下的sql语句，

   insert 
    into
        goods
        (goods_price, goods_name, goods_description) 
    values
        (?, ?, ?)

   update
        goods 
    set
        goods_price=?,
        goods_name=?,
        goods_description=? 
    where
        goods_id=?

如果把属性修改为true，则hibernat在生成insert语句时，会根据持久化类的属性，如果属性的值为null，则生成不插入该字段的sql语句，在更新的时候，如果该实体在session管理中，修改某个属性，则只生成修改该字段的更新语句，而不是把所有的属性都更新。

      insert 
    into
        goods
        (goods_name) 
    values
        (?)

   update
        goods 
    set
        goods_name=? 
    where
        goods_id=?

如果使用jpa，使用注解元数据的话，则要使用hibernate提供的注解，实体代码如下

  package com.own.model;


import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@org.hibernate.annotations.Entity(dynamicInsert=true,dynamicUpdate=true)
@Table(name="goods")
public class Goods implements Serializable {
	
	
	private static final long serialVersionUID = 1L;
	private Integer id;
	private  String goodsName;
	private Double price;
	private String goodsDescription;	
	
	public Goods(){}
	
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="goods_id")
	public Integer getId() {
		return id;
	}
	
	public void setId(Integer id) {
		this.id = id;
	}
	
	@Column(name="goods_name",length=40,nullable=false)
	public String getGoodsName() {
		return goodsName;
	}
	public void setGoodsName(String goodsName) {
		this.goodsName = goodsName;
	}
	
	@Column(name="goods_price")
	public Double getPrice() {
		return price;
	}
	public void setPrice(Double price) {
		this.price = price;
	}
	
	@Column(name="goods_description")
	public String getGoodsDescription() {
		return goodsDescription;
	}
	public void setGoodsDescription(String goodsDescription) {
		this.goodsDescription = goodsDescription;
	}

	
	@Override
	public boolean equals(Object o) {
		
		if(o == null || o.getClass() != this.getClass()){
			return false;
		}
		
		if(o == this){
			return true;
		}
		
		Goods goods = (Goods) o;
		
		if(id == null ? goods.id == null : this.id.equals(goods.id)){
			return true;
		}
		
		
		return false;
	}
	
	@Override
	public int hashCode() {
		return this.id.hashCode()  ;
	}
	
}

加上这两个属性，就避免了当数据表中字段很多的情况下，更新没有修改的字段，插入的时候，就不生成插入属性为null的字段。