Grails 2抽象域继承问题 [英] Grails 2 abstract domain inheritance issue

问题描述

在Grails中使用抽象（或非抽象）继承时，以下方法对我不适用。

很快，我的继承如下所示：

 抽象BaseClass {...} 
 SomeClass extends BaseClass {...} 
 SomeOtherClass extends BaseClass {...} 
  

然后在另一个域对象中：

  ThirdClass {
 ... 
 BaseClass baseProperty 
 ... 
} 
  

但是现在，当我尝试将该属性设置为 SomeClass 或 SomeOtherClass 实例，Grails包含：

错误util.JDBCExceptionReporter - 无法添加或更新子行：外键约束失败
...

这是不可能的吗？

---

我也试过让基类不是抽象的，而且还试过casti将 SomeClass 或 SomeOtherClass 实例更改为 BaseClass 。它们会产生相同的错误。

---

更新

我刚刚查过。它适用于我添加的第一个子类。但是，只要我尝试添加其他子类，它就会失败。

换句话说：

<$ p $ b $ def prop1 = new ThirdClass（baseProperty：instanceOfSomeClass）.save（）


工作正常。但是，当我尝试做：

pre $ def prop2 = new ThridClass（baseProperty：instanceOfSomeOtherClass）.save（）


失败。

---

更新2

进一步调查显示表创建过程中出现问题。它正确地将两个外键添加到 ThirdClass 表中，但是键错误地引用了：

  CONSTRAINT`...`FOREIGN KEY（`some_id`）参考`base_class`（`id`），
 CONSTRAINT`...`FOREIGN KEY（`some_id`）REFERENCES`some_class`（`不知道为什么选择基类和其中一个子类？为什么选择基类和其中一个子类？我试过清洗等。
     首先，创建您的BaseClass  outside 域结构。它必须是一个外部类，放在脚本文件夹，源文件夹中。
  package com.example.model 
 
 / ** 
 * @author Inocencio 
 * / 
 class BaseClass {
 
 Date createdAt = new Date（）
 
} 
  
现在，创建一个常规的域类并扩展它。
  package com.example.domain 
 
 import com.example.model.BaseClass 
 $ b $ class SomeClass extends BaseClass {
 
字符串名称
 
静态约束= {
名称（可空值：false）
} 
 
} $ b $正如你所看到的，一旦你坚持SomeClass一个createdAt字段被填充和保存，以及。 
检查测试课出：
  @TestFor（SomeClass）
类SomeClassTests {
 
 void testSomething（）{
 def some = new SomeClass（）
 some.name =Hello There
 some.save（）
 
 //找到它
 def someFind = SomeClass.list（）[0] 
 
 assert someFind 
 
 assertTrue someFind.createdAt！= null 
 
 // println Date：$ someFind.createdAt
 // printlnName：$ someFind.name
} 
} 
  
我希望这可以帮上忙。
 
The following is not working for me when using abstract (or non-abstract for that matter) inheritance in Grails.

Very quickly, my inheritance is as follows:
abstract BaseClass               { ... }
SomeClass      extends BaseClass { ... }
SomeOtherClass extends BaseClass { ... }
And then in another domain object:
ThirdClass {
    ...
    BaseClass baseProperty
    ...
}
But now, when I try to set that property to either a SomeClass or SomeOtherClass instance, Grails compains:

  
ERROR util.JDBCExceptionReporter  - Cannot add or update a child row: a foreign key constraint fails
  ...
Is this not possible?



I have also tried having the base class not be abstract, and also tried casting the SomeClass or SomeOtherClass instances to BaseClass. They generate the same error.



UPDATE

I just checked. It works for the first sub-class that I add. But as soon as I try to add the other sub-class it fails.

In other words:
def prop1 = new ThirdClass(baseProperty: instanceOfSomeClass).save()
works fine. But when I then try and do:
def prop2 = new ThridClass(baseProperty: instanceOfSomeOtherClass).save()
it fails.



UPDATE 2

Further investigation shows that something goes wrong during the table creation process. It correctly adds two foreign keys to the ThirdClass table, but the keys incorrectly references:
CONSTRAINT `...` FOREIGN KEY (`some_id`) REFERENCES `base_class` (`id`),
CONSTRAINT `...` FOREIGN KEY (`some_id`) REFERENCES `some_class` (`id`)
Don't know why it's choosing the base class and one of the sub-classes? I have tried cleaning etc.
解决方案
First of all, create your BaseClass outside domain structure. It must be an external class, put it on script folder, source folder.
package com.example.model

/**
 * @author Inocencio
 */
class BaseClass {

    Date createdAt = new Date()

}
Now, create a regular domain class and extend it.
package com.example.domain

import com.example.model.BaseClass

class SomeClass extends BaseClass {

    String name

    static constraints = {
        name(nullable: false)
    }

}
As you can see, once you persist SomeClass a createdAt field is filled and saved as well. Check the test class out:
@TestFor(SomeClass)
class SomeClassTests {

    void testSomething() {
        def some = new SomeClass()
        some.name = "Hello There"
        some.save()

        //find it
        def someFind = SomeClass.list()[0]

        assert someFind

        assertTrue someFind.createdAt != null

//        println "Date: $someFind.createdAt"
//        println "Name: $someFind.name"
    }
}
I hope it can be helpful.

                        
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