one-to-one双向关联之加载 - 数据库编程

nd_id, name] 2014-02-04 16:52:21 INFO org.hibernate.tool.hbm2ddl.TableMetadata:69 - HHH000108: Foreign keys: [fk_fi3kodkmubgryyblf4935y4dk] 2014-02-04 16:52:21 INFO org.hibernate.tool.hbm2ddl.TableMetadata:70 - HHH000126: Indexes: [pk__t_wife__3213e83f1332dbdc] 2014-02-04 16:52:21 INFO org.hibernate.tool.hbm2ddl.SchemaUpdate:242 - HHH000232: Schema update complete Hibernate: select husband0_.id as id1_0_0_, husband0_.name as name2_0_0_, wife1_.id as id1_1_1_, wife1_.husband_id as husband_3_1_1_, wife1_.name as name2_1_1_ from t_husband husband0_ left outer join t_wife wife1_ on husband0_.id=wife1_.husband_id where husband0_.id= ***************** Hibernate: select wife0_.id as id1_1_0_, wife0_.husband_id as husband_3_1_0_, wife0_.name as name2_1_0_, husband1_.id as id1_0_1_, husband1_.name as name2_0_1_ from t_wife wife0_ left outer join t_husband husband1_ on wife0_.husband_id=husband1_.id where wife0_.id= Hibernate: select wife0_.id as id1_1_1_, wife0_.husband_id as husband_3_1_1_, wife0_.name as name2_1_1_, husband1_.id as id1_0_0_, husband1_.name as name2_0_0_ from t_wife wife0_ left outer join t_husband husband1_ on wife0_.husband_id=husband1_.id where wife0_.husband_id=
首先加载husband对象时会把相关联的字段全部加载出来。

但是可以看出来加载wife表的时候会执行两次查询，虽然这两次查询的内容是一样的，但是第一次是查询出的是主表的信息，第二次是为了查出从表信息，这是hibernate的默认加载策略，因为t_wife表有外键，如果加载的表有从表，他会默认加载同时夹在两个表的信息。是否加载从表信息是由fetch进行设置的。

我们把wife类one-to-one新添加一个属性

/**
 * 
 */
package com.maybe.test_1;

import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;

/**
 * @author MayBe
 *
 * function:
 */
@Entity
@Table(name="t_wife")
public class Wife {
	
	private Integer id;
	private String name;
	private Husband husband;
	@Id
	@GeneratedValue
	public Integer getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public void setName(String name) {
		this.name = name;
	}
	@OneToOne(fetch=FetchType.LAZY)
	public Husband getHusband() {
		return husband;
	}
	public void setHusband(Husband husband) {
		this.husband = husband;
	}
	
}

我们把抓取方式改成懒抓取，加载输出如下所示：

2014-02-04 17:07:38 INFO org.hibernate.tool.hbm2ddl.SchemaUpdate:182 - HHH000228: Running hbm2ddl schema update
2014-02-04 17:07:38 INFO org.hibernate.tool.hbm2ddl.SchemaUpdate:193 - HHH000102: Fetching database metadata
2014-02-04 17:07:38 INFO org.hibernate.tool.hbm2ddl.SchemaUpdate:205 - HHH000396: Updating schema
2014-02-04 17:07:39 INFO org.hibernate.tool.hbm2ddl.TableMetadata:66 - HHH000261: Table found: hibernate.dbo.t_husband
2014-02-04 17:07:39 INFO org.hibernate.tool.hbm2ddl.TableMetadata:67 - HHH000037: Columns: [id, name]
2014-02-04 17:07:39 INFO org.hibernate.tool.hbm2ddl.TableMetadata:69 - HHH000108: Foreign keys: []
2014-02-04 17:07:39 INFO org.hibernate.tool.hbm2ddl.TableMetadata:70 - HHH000126: Indexes: [pk__t_husban__3213e83f0f624af8]
2014-02-04 17:07:40 INFO org.hibernate.tool.hbm2ddl.TableMetadata:66 - HHH000261: Table found: hibernate.dbo.t_wife
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one-to-one双向关联之加载(二)