JPA实体的自定义映射规则 [英] custom mapping rule for JPA entity

问题描述

我想为JPA实体映射设置一些实体规则.一个非常简单的例子是，如果有一个实体

I want to set some entity rules for JPA entity mapping. Very simple example would be if have an entity

@Entity
@Table(name = "my_table")
public class {
   @Id
   private Integer id;
   private boolean flagged;
   ....

  }

我标记的值是db中标记为Yes/null/No的String.如果值是null/是，我希望将我标记的值设置为true.否则为假.有什么方法可以在JPA实体的bean映射上定义此自定义规则.这是一个简单的示例，也需要将其用于复杂的规则.感谢您的帮助.

my flagged value is String in db marked as Yes/null/No. I want my flagged value to be set as true if value null/yes. false otherwise. Is there any way to define this custom rule on bean mapping for JPA entities. This is a simple example, would need to use this for complex rules as well. Appreciate your help.

谢谢

推荐答案

您可以编写自己的转换器.使用下面的代码作为起点并适应您的用例

You could write your own converter. Use the code below as a start point and adapt to your use case

@Entity
@Table(name = "my_table")
public class Myclass{    

  @Convert(converter=BoolToString.class)
  private Boolean flagged;    
  ...

}

转换器为:

  @Converter
  public class BoolToString implements AttributeConverter<Boolean, 
String> {
  @Override
  public String convertToDatabaseColumn(Boolean value) {
  if (value == null) return "-";
  else return value ? "Y" : "N";
 }

 @Override
 public Boolean convertToEntityAttribute(String value) {
  if (value.equals("-") return null;
  else if (value.equals("Y")) return true;
  else if (value.equals("N")) return false;
  else throw new IllegalStateException("Invalid boolean character: " + 
  value);
 }

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