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？
最佳答案
关于database-design - 如何定义一个 m :n relation with additional attributes in Squeryl?，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/6570882/