为Hibernate实体的特定字段设置查询 [英] Setting up query for specific field of Hibernate entity

问题描述

我使用spring和hibernate。出现以下情况，我不知道是否真的有可能实施。例如，有一个hibernate实体

  @Entity 
 public class TestEntity {
 private String field1; 
私人字符串field2; 
 private String specField; 
 
 @Column（name =field1）
 public String getField1（）{
 return field1; 
 
 
 @Column（name =field2）
 public String getField2（）{
 return field2; 
 
 
 public String getSpecField（）{
 return（field1！= null？field1：field2）; 
 
 
 
 
 $ b $ p 
 $ b 
我需要specField的值由SQL查询而不是java代码。 
类似于此 
 
 
  @Entity 
 public class TestEntity {
 private String field1; 
私人字符串field2; 
 private String specField; 
 
 @Column（name =field1）
 public String getField1（）{
 return field1; 
 
 
 @Column（name =field2）
 public String getField2（）{
 return field2; 
 
 
 @Query（value =COALESCE（field1，field2））
 public String getSpecField（）{
 return specField; 
 
 
  
我被告知应该有能力这样做。但没有发现任何证实此事的事情。  
 
 
究竟查询的确实不重要。我需要specField将被一些查询，而不是由java代码。 
 
 
 
感谢您的帮助。
 
 
更新感谢@premkumar，提醒您使用@Formula 
所以现在我有
 
 
  @Entity 
 public class TestEntity {
 private String field1; 
私人字符串field2; 
 private String specField; 
 
 @Column（name =field1）
 public String getField1（）{
 return field1; 
 
 
 @Column（name =field2）
 public String getField2（）{
 return field2; 
 
 $ b @Formula（COALESCE（field2，field2））
 public String getSpecField（）{
 return（field1！= null？field1：field2） ; 
 
 
 
 
 
 
 $ 
但是应用程序无法从使用$ b初始化bean初始化$ b NullPointerException在org.springframework.orm.hibernate3.LocalSessionFactoryBean.newSessionFactory 
 
 
 
我也试过以下内容： 
 
 
 
 
 
将公式放在private String specField上面 - 应用程序已启动，但hibernate失败，无法在数据库中找到spec_field 
  
 
 
将@Formula和@Transient放在getter  -  app开始，没有错误，但specField始终为空。它看起来像hibernate完全忽略了它。
    如果你使用hibernate，请尝试以下操作：
 
 $ pre $ lt; code> @Formula（COALESCE（field1，field2））
 public String getSpecField（）{ 
返回specField; 
} 
  
注意： - 据我所知，在JPA中没有其他选择。注意这会混淆hibernate和jpa注释。
 
I use spring and hibernate. The following situation occured and I don't know if it's really possible to implement. Will appreciate any help.

For example, there is a hibernate entity
    @Entity
public class TestEntity {
    private String field1;
    private String field2;
    private String specField;

    @Column(name = "field1")
    public String getField1() {
        return field1;
    }

    @Column(name = "field2")
    public String getField2() {
        return field2;
    }

    public String getSpecField() {
        return (field1 != null ? field1 : field2);
    }
}
And I need the value for specField to be generated by SQL query and not by java code. 
Something like this
    @Entity
public class TestEntity {
    private String field1;
    private String field2;
    private String specField;

    @Column(name = "field1")
    public String getField1() {
        return field1;
    }

    @Column(name = "field2")
    public String getField2() {
        return field2;
    }

    @Query(value= "COALESCE(field1, field2)")
    public String getSpecField() {
        return specField;
    }
}
I was told that there should be ability to do so. But didn't find anything that approves this. 

it's not actually important what exactly query does. I need that specField will be taken by some query and not by java code. Is it possible?

Thanks for help.

UPDATE Thanks to @premkumar, for advicing to use @Formula
So now I have 
@Entity
public class TestEntity {
    private String field1;
    private String field2;
    private String specField;

    @Column(name = "field1")
    public String getField1() {
        return field1;
    }

    @Column(name = "field2")
    public String getField2() {
        return field2;
    }

    @Formula("COALESCE(field2, field2)")
    public String getSpecField() {
        return (field1 != null ? field1 : field2);
    }
}
But app fails to start on bean initialization with 
NullPointerException at org.springframework.orm.hibernate3.LocalSessionFactoryBean.newSessionFactory

I tried also the following:

Put formula above "private String specField" - app started, but hibernate failed on could not find spec_field in database
Put @Formula and @Transient on getter - app started, no errors, but specField is always null. It looks like hibernate totally ignored it

解决方案
If you are using hibernate, try the following: 
@Formula("COALESCE(field1, field2)")
public String getSpecField() {
    return specField;
}
Note:- As far as I know there is no alternative in JPA. Beware this will mixup hibernate and jpa annotations.

                        
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