grails - Grails GORM：如何创建复合主键并将其用于表关系？

Question

我有两个表，其中一个（旧表：A）有两个字段应该用作复合外键，另一个（新表：B）应该使用复合主键来建立each row:A has one row:B关系。我如何用 GORM 来描述这些表？

到目前为止，我已经能够创建一个反映遗留表的域类：A

class A {

    ...
    //composite foreign key to link B class
    String className;
    String eventName;

    B b; //instance of B to be related

    static mapping = {
        table 'a_table';            
        id column: 'id';
        className column: 'class_name';
        eventName column: 'event_name';
        //b: ???
    }
}

哪个有效，但我无法创建new class:B和关系。

我试图将 B 声明为：

class B implements Serializable{

    static auditable = true;

    String name;
    String className;
    String eventName;

    static mapping = {
        //supposed to make a composite PK
        id composite:[className, eventName] 
    }
}

但这不会编译
ERROR context.GrailsContextLoader - Error executing bootstraps: Error evaluating ORM mappings block for domain [com.package.B]: No such property: eventName for class: org.codehaus.groovy.grails.orm.hibernate.cfg.HibernateMappingBuilder

我想要的是这样的：

static mapping = {
    ...
    b composite: [b.className:className, b.eventName:eventName]
    //or whatever is the right way for this to be done.
}

让 A 类让 GORM 处理这种关系。

Answer 1

您是否尝试使用属性名称而不是使用属性值？

class B implements Serializable{
    String name;
    String className;
    String eventName;

    static mapping = {
        //supposed to make a composite PK
        id composite:['className', 'eventName'] 
    }
}

并在 A 中映射：

class A {
    static hasMany = [ b : B ]
}

无需拥有className或eventName在A

Answer 2

B 类必须声明为 Serializable 并实现 equals 和 hashCode 方法

import org.apache.commons.lang.builder.HashCodeBuilder
class B implements Serializable{

    static auditable = true;

    String name;
    String className;
    String eventName;
    boolean equals(other) {
    if (!(other instanceof B)) {
        return false
    }

    other.className == className && other.eventName == eventName
    }

    int hashCode() {
    def builder = new HashCodeBuilder()
    builder.append className
    builder.append eventName
    builder.toHashCode()
    }

    static mapping = {
        //supposed to make a composite PK
        id composite:["className", "eventName"] 
    }
}

并且A类必须具有B类的属性，而GORM制作复合外键

class A {

    //composite foreign key to link B class
    B b; //instance of B to be related

    static mapping = {
        table 'a_table';            
        id column: 'id';
    }
}

它在数据库中创建两个表

+--------------------------------------------------+
|                       A_TABLE                    |  
+--------+-----------+--------------+--------------+
|   id   |  version  |  b_className | b_eventName  |
+--------+-----------+--------------+--------------+
--where the Primary key is "id" and the foreign key are "b_className and b_eventName" 
+--------------------------------------------------+
|                       B                          |  
+--------+-----------+--------------+--------------+
|  name  |  version  |  className   | eventName    |
+--------+-----------+--------------+--------------+
--where the Primary key are "className and eventName" 

如果您要将列的名称更改为其他名称，只需在映射语句中添加分句

class A {

    //composite foreign key to link B class
    B b; //instance of B to be related

    static mapping = {
        table 'a_table';            
        id column: 'id';
        columns {
              b {
                 column name: "className"
                 column name: "eventName"
              }
        }
    }
}

Answer 3

import org.apache.commons.lang.builder.HashCodeBuilder
class Person implements Serializable {

String firstName
String lastName

boolean equals(other) {
    if (!(other instanceof Person)) {
        return false
    }

    other.firstName == firstName && other.lastName == lastName
}

int hashCode() {
    def builder = new HashCodeBuilder()
    builder.append firstName
    builder.append lastName
    builder.toHashCode()
}

static mapping = {
    id composite: ['firstName', 'lastName']
}
}

这是你可以从 grails 的官方文档中找到的，

http://grails.org/doc/latest/guide/GORM.html#compositePrimaryKeys

只是盲目地遵循这一点，你的问题就会得到解决。解释参考上面的链接