JPA如何为可嵌入对象提供继承关系 [英] JPA how to supply inheritance relationships for embeddable objects

问题描述

我有一个抽象类BaseUnit来表示我的应用程序中的每个单元。我将它定义为 @MappedSuperclass 。

  @MappedSuperclass 
公共类BaseUnit实现UnitMultiplierInterface ，可序列化{
 / ** 
 * 
 * / 
 private static final long serialVersionUID = -2648650210129120993L; 
 @Enumerated（EnumType.STRING）
 private UnitMultiplier乘数; 
 @Enumerated（EnumType.STRING）
私人UnitSymbol单位; 
 @Column（name =value）
 private double value; 
 
 @Override 
 public void setMultiplier（UnitMultiplier multiplier）{
 this.multiplier = multiplier; 
} 
 
 @Override 
 public UnitMultiplier getMultiplier（）{
 return multiplier; 
} 
 
 @Override 
 public void setUnit（UnitSymbol unit）{
 this.unit = unit; 
} 
 
 @Override 
 public UnitSymbol getUnit（）{
 return unit; 
} 
 
 @Override 
 public void setValue（double currentL1）{
 this.value = currentL1; 
} 
 
 @Override 
 public double getValue（）{
返回值; 
}} 
  

我有一些子类型，例如百分比，阻力。

百分比：我将它定义为@Embeddable

  @可嵌入的
 public class Percentage extends BaseUnit {
 / ** 
 * 
 * / 
 private static final long serialVersionUID = 2693623337277305483L; 
 
 public百分比（）{
 super（）; 
} 
 
 public百分比（双值）{
 setUnit（UnitSymbol.Percentage）; 
 setValue（value）; 
} 
  

}

的电阻：即可。我将它定义为@Embeddable

  @Embeddable 
公共类阻力扩展BaseUnit {
 / ** 
 * 
 * / 
 private static final long serialVersionUID = -4171744823025503292L; 
 
 public Resistance（）{
 super（）; 
} 
 
公众抵抗（双值）{
 setUnit（UnitSymbol.Ohm）; 
 setValue（value）; 
} 
  

}

  @Entity 
公共类A实现Serializable {
 / ** 
 * 
 * / 
 private static final long serialVersionUID = 5167318523929930442L; 
 @Id 
 @GeneratedValue 
 @Column（name =id）
私人长ID; 
 @嵌入
私人抵抗; 
 @Embedded 
 / **方案阻力。 * / 
私人百分比; 
  

}

现在，我的问题是你认为这个jpa定义可以毫无问题地工作吗？或者你能告诉我最正确的方法来达到我的要求吗？ 更好的方法是将 @Embeddable 和 @MappedSuperclass ，然后以两种不同的方式使用它。如果百分比需要与阻力类似，那么根本不需要 @MappedSuperClass ，但如果不相似，则可以通过以下方式达到要求。 p>

  @MappedSuperclass 
 @Embeddable 
公共类BaseUnit实现Serializable {
 ... 
} 
  

案例1：BaseUnit作为主键

  @Entity 
 public class AWithResistance实现可序列化{
 
 @EmbeddedId 
私有BaseUnit键; 
 .... 
} 
  

案例2：BaseUnit as Super Class继承公共属性

  @Entity 
公共类AWithPercentage扩展BaseUnit实现Serializable {
 .... 
} 
  

I have an abstract class "BaseUnit" to represent each unit in my application. I have defined it as @MappedSuperclass.

@MappedSuperclass
public class BaseUnit implements UnitMultiplierInterface, Serializable {
/**
 * 
 */
private static final long serialVersionUID = -2648650210129120993L;
@Enumerated(EnumType.STRING)
private UnitMultiplier multiplier;
@Enumerated(EnumType.STRING)
private UnitSymbol unit;
@Column(name = "value")
private double value;

@Override
public void setMultiplier(UnitMultiplier multiplier) {
    this.multiplier = multiplier;
}

@Override
public UnitMultiplier getMultiplier() {
    return multiplier;
}

@Override
public void setUnit(UnitSymbol unit) {
    this.unit = unit;
}

@Override
public UnitSymbol getUnit() {
    return unit;
}

@Override
public void setValue(double currentL1) {
    this.value = currentL1;
}

@Override
public double getValue() {
    return value;
}}

I have some subtypes like Percentage, Resistance.

Percentage: I have defined it as @Embeddable

@Embeddable
public class Percentage extends BaseUnit {
/**
 * 
 */
private static final long serialVersionUID = 2693623337277305483L;

public Percentage() {
    super();
}

public Percentage(double value) {
    setUnit(UnitSymbol.Percentage);
    setValue(value);
}

}

Resistance:. I have defined it as @Embeddable

@Embeddable
public class Resistance extends BaseUnit {
/**
 * 
 */
private static final long serialVersionUID = -4171744823025503292L;

public Resistance() {
    super();
}

public Resistance(double value) {
    setUnit(UnitSymbol.Ohm);
    setValue(value);
}

}

I can use same/different unit type while defining an entity.Here is an example.

@Entity
public class A implements Serializable {
/**
 * 
 */
private static final long serialVersionUID = 5167318523929930442L;
@Id
@GeneratedValue
@Column(name = "id")
private long id;
@Embedded
private Resistance resistance;
@Embedded
/** resistance of scenario. */
private Percentage percentage;

}

Now, my question do you think this jpa definitions can work without problem? Or can you please tell me most proper way to achieve my requirement?

解决方案

A better way is to mix both @Embeddable and @MappedSuperclass in your abstract class and then use it in 2 different ways. If Percentage needs to be similar to Resistance, then you wouldn't need @MappedSuperClass at all but if not similar, then below is the way you can achieve the requirement.

@MappedSuperclass
@Embeddable
public class BaseUnit implements Serializable {
...
}

Case 1: BaseUnit as Primary Key

@Entity 
public class AWithResistance implements Serializable {

@EmbeddedId
private BaseUnit key;
....
}

Case 2: BaseUnit as Super Class to inherit common properties

@Entity 
public class AWithPercentage extends BaseUnit implements Serializable {
....
}

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