混合连接和单个表继承和查询所有对象 [英] mixing joined and single table inheritance and querying for all objects

问题描述

我有一个正在使用以下配置的web应用程序（我更改了实体名称）：

  @Entity 
 @Inheritance（strategy = InheritanceType.JOINED）
 @Table（name =animals）
 public abstract class Animal {... 
 
 @MappedSuperclass 
 @Inheritance（strategy = InheritanceType.SINGLE_TABLE）
 @DiscriminatorColumn（name =type）
 public abstract class Mammal extends Animal {... 
 
 @Entity 
 @Table（name =mammals）
 @PrimaryKeyJoinColumn（name =mammal_id）
 @DiscriminatorValue（value =dog）
 public class Dog extends Mammal {... 
 
 @Entity 
 @Table（name =mammals）
 @PrimaryKeyJoinColumn（name =mammal_id）
 @DiscriminatorValue（value =cat）
公共类Cat延伸Mammal {... 
  

所以我有2个表格：动物和哺乳动物。
这种配置正在工作，除非我完全不了解。
哺乳动物中的继承类型从JOINED变为SINGLE_TABLE，所以猫和狗都存储在哺乳动物表中与哺乳动物表连接在一起。

问题是不可能以多态的方式检索哺乳动物（猫或狗）：

 哺乳动物哺乳动物=（哺乳动物）hibernateTemplate .get（Mammal.class，id）; 
  

或者带有单个Hibernate查询的哺乳动物（狗和猫）列表：

 列表< Mammal> list =（List ）hibernateTemplate.find（from Mammal）; 
  

我得到：未知实体：哺乳动物，因为哺乳动物不是实体，它只是一个映射的超类。

我尝试了几个配置更改，例如下面的配置。这似乎是有道理的，但在这种情况下，我得到无法加载实体：哺乳动物，因为它寻找表猫和狗（不存在）。

 @Entity 
 @Inheritance（strategy = InheritanceType.JOINED）
 @Table（name =animals）
 public abstract class Animal {... 
 
 @Entity 
 @Inheritance（strategy = InheritanceType.SINGLE_TABLE）
 @Table（name =mammals）
 @PrimaryKeyJoinColumn（name =mammal_id）
 @DiscriminatorColumn（name =type）
 public abstract class Mammal extends Animal {... 
 
 @Entity 
 @DiscriminatorValue（value =dog）
 public class Dog扩展Mammal {... 
 
 @Entity 
 @ DiscriminatorValue（value =cat）
公共类Cat扩展哺乳动物{... 
  

因此，总结一下：我想保持webapp的工作方式相同（2个表格：动物和哺乳动物）但同时能够做一个多态的查询：用一个检索哺乳动物（猫和狗）的列表查询。

我希望我已经清楚了，并且提前感谢您提供任何帮助。

另一个尝试：

涉及以下表格的外键循环依赖：

  @实体
 @Inheritance（strategy = InheritanceType.JOINED）
 @Table（name =animals）
 public abstract class Animal {... 
 
 @Entity 
 @Table（name =mammals）
 @PrimaryKeyJoinColumn（name =mammal_id）
 @Inheritance（strategy = InheritanceType.SINGLE_TABLE）
 @DiscriminatorColumn（name =type ）
 public abstract class Mammal extends Animal {... 
 
 @Entity 
 @Table（name =mammals）
 @DiscriminatorValue（value =dog ）
 public class Dog extends Mammal {... 
 
 @Entity 
 @Table（name =mammals）
 @DiscriminatorValue（value =cat） 
 public class Cat extends Mammal {... 
  

解决方案

你有没有试过 hibernateTemplate.find（来自Mammal ）？

您的 find 查询需要根据 JPA实体不是表名。

BTW表格通常以单数形式命名 - 它通常会使复杂查询读得更好一些 - 例如 WHERE chicken.id = egg.id

I have a webapp that is working with the following configuration (I changed the entity names):

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@Table(name = "animals")
public abstract class Animal { ...

@MappedSuperclass
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type")
public abstract class Mammal extends Animal { ...

@Entity
@Table(name = "mammals")
@PrimaryKeyJoinColumn(name = "mammal_id")
@DiscriminatorValue(value = "dog")
public class Dog extends Mammal { ...

@Entity
@Table(name = "mammals")
@PrimaryKeyJoinColumn(name = "mammal_id")
@DiscriminatorValue(value = "cat")
public class Cat extends Mammal { ...

So I have 2 tables: animals and mammals. This configuration is working, unless I don't completely understand how. The inheritance type is changed from JOINED to SINGLE_TABLE in Mammal, so cats and dogs are stored in mammals table joined with animals table by mammal_id column.

The problem is that is not possible to retrieve a mammal (cat or dog) in a polymorphic way:

Mammal mammal = (Mammal) hibernateTemplate.get(Mammal.class, id);

or a list of mammals (dogs and cats) with a single Hibernate query:

List<Mammal> list = (List<Mammal>) hibernateTemplate.find("from Mammal");

I get: "Unknown entity: Mammal", because Mammal is not an entity, it is just a mapped super class.

I tried several changes in configuration for example the one below. This seems to make sense, but in that case I got "Could not load entity: Mammal" because it looks for tables cats and dogs (which doesn't exist).

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@Table(name = "animals")
public abstract class Animal { ...

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@Table(name = "mammals")
@PrimaryKeyJoinColumn(name = "mammal_id")
@DiscriminatorColumn(name = "type")
public abstract class Mammal extends Animal { ...

@Entity
@DiscriminatorValue(value = "dog")
public class Dog extends Mammal { ...

@Entity
@DiscriminatorValue(value = "cat")
public class Cat extends Mammal { ...

So, to summarize: I want to keep the webapp working the same way (2 tables: animals and mammals) but at the same time be able to do a polymorphic query: retrieve a list of mammals (cats and dogs) with one query.

I hope I was clear enough and thanks in advance for any help.

ANOTHER TRY:

"Foreign key circularity dependency involving the following tables: "

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@Table(name = "animals")
public abstract class Animal { ...

@Entity
@Table(name = "mammals")
@PrimaryKeyJoinColumn(name = "mammal_id")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type")
public abstract class Mammal extends Animal { ...

@Entity
@Table(name = "mammals")
@DiscriminatorValue(value = "dog")
public class Dog extends Mammal { ...

@Entity
@Table(name = "mammals")
@DiscriminatorValue(value = "cat")
public class Cat extends Mammal { ...

解决方案

Did you try hibernateTemplate.find("from Mammal") ?

Your find query needs to be in terms of JPA entities not table names.

BTW tables are typically named in the singular - it generally makes complex queries read a bit better - e.g. WHERE chicken.id = egg.id

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