database-design - 如何定义一个 m :n relation with additional attributes in Squeryl?

Question

给定一个具有 m:n 关系的旧数据库和该关系的一些附加属性，如何用 squeryl.最后，表格应如下所示:

   +--------------+      +---------------+      +----------------+   | TableA       |      | Rel_A_B       |      | TableB         |   +--------------+ ____ +---------------+ ____ +----------------+   | id: Int      |      | tableA: int   |      | compkey_1: int |   | (more attrs) |      | tableB_1: int |      | compkey_2: int |   +--------------+      | tableB_2: int |      | (more attrs)   |                         | value: Varchar|      +----------------+                         | date: Date    |                         +---------------+

Theres no problem in defining the three tables manually with squeryl. However, as far as I understand the documentation at the moment (0.9.4) there is no possibility to define a many-to-many relationship with additional attributes for the relation.

That's why I defined three tables and two one-to-many relations:

// TableA
class TableA(val id: Int, ...) extends KeyedEntity[Int] {
    def this() = this(0, ...)
}

// TableB
class TableB(val compkey1: Int, val compkey2: Int, ...) 
        extends KeyedEntity[CompositeKey2[Int, Int]] {

    def id = CompositeKey2(compkey1, compkey2)
}

// Rel_A_B
class RelAB(val tabA: Int, val tabB1: Int, val tabB2: Int, val value: String, 
            val date: Date) extends KeyedEntity[CompositeKey3[Int, Int, Int]] {

    def id = CompositeKey3(tabA, tabB1, tabB2)
}

定义 TableA 和 RelAB 之间的关系很容易。我使用普通的一对多关系:

val relA =
    oneToManyRelation(tableA, relAB).
    via((a, r) => a.id === r.tableA)

但我没有看到定义第二个关系的方法。我已经尝试在仅包含 tableB 中的列的关系表(名为 compkeyB)上定义一个额外的复合值，并将其与 tableB 的复合键进行比较，但这不起作用:

val relB =
    oneToManyRelation(tableB, relAB).
    via((b, r) => b.id === r.compkeyB)

它抛出一个“类型不匹配”异常:

found   : org.squeryl.dsl.ast.LogicalBoolean
required: org.squeryl.dsl.ast.EqualityExpression

任何想法如何解决这个问题？

Answer 1

你被这个限制咬了:

http://www.assembla.com/spaces/squeryl/tickets/25-compositekeys-cannot-be-the-binding-expression-for-relations