如何改善這種嘗試在蛋糕圖案

Question

這是我實現斯卡拉蛋糕模式早期的嘗試之一：

trait dbConfig { 
    val m: Model = ??? 
} 

trait testDB extends dbConfig { 
    override val m = new Model(Database.forURL("jdbc:h2:mem:testdb", driver = "org.h2.Driver")) 
    m.cleanDB 
} 

trait productionDB extends dbConfig { 
    override val m = new Model(Database.forURL("jdbc:postgresql:silly:productionDB", driver = "org.postgresql.Driver")) 
} 

trait SillySystem extends HttpService with dbConfig { 
.... 
// System logic 
.... 
} 

這將允許我使用我的服務這樣的測試時：

class TestService extends SillySystem with testDB { 
..... 
} 

而且這樣生產：

class ProductionService extends SillySystem with productionDB { 
..... 
} 

這工作，但我在做正確嗎？

Answer 1

這可能是有益的，使DbConfig抽象和使用defsince一個可以覆蓋def與val或lazy val，而不是倒過來。

SillySystem is not a DbConfig，所以使用依賴注入而不是繼承。

trait DbConfig { 
    def m: Model // abstract 
} 

trait TestDB extends DbConfig { 
    // you can override def with val 
    val m = new Model(Database.forURL("jdbc:h2:mem:testdb", driver = "org.h2.Driver")) 
    m.cleanDB 
} 

trait ProductionDB extends DbConfig { 
    val m = new Model(Database.forURL("jdbc:postgresql:silly:productionDB", driver = "org.postgresql.Driver")) 
} 

trait SillySystem extends HttpService { 
    this: DbConfig => // self-type. SillySystem is not a DbConfig, but it can use methods of DbConfig. 
.... 
// System logic 
.... 
} 

val testService = new SillySystem with TestDB 

val productionService = new SillySystem with ProductionDB 

val wrongService1 = new SillySystem // error: trait SillySystem is abstract; cannot be instantiated 
val wrongService2 = new SillySystem with DbConfig // error: object creation impossible, since method m in trait DbConfig of type => Model is not defined 

val correctService = new SillySystem with DbConfig { val m = new Model(...) } // correct