光滑的左外部联接获取整个联接行作为选项 [英] Slick left outer join fetching whole joined row as option

问题描述

我的加入看起来像这样:

My join looks like this:

def byIdWithImage = for {
    userId <- Parameters[Long]
    (user, image) <- Users leftJoin RemoteImages on (_.imageId === _.id) if user.id === userId
} yield (user, image)

但是当user.imageId为null时，滑动会在运行时失败

but slick fails at runtime when user.imageId is null

[SlickException:读取列RemoteImage.url的NULL值]

[SlickException: Read NULL value for column RemoteImage.url]

将产量更改为

} yield (user, image.?)

为我提供了一个编译时异常，它仅适用于单个列

gives me a compile time exception, it only works on individual columns

找不到类型为scala.slick.lifted.TypeMapper [image.type]的证据参数的隐含值

could not find implicit value for evidence parameter of type scala.slick.lifted.TypeMapper[image.type]

会有其他方法来完成我在这里要做的事情吗? (在单个查询中)

Would there be a different way to accomplish what I'm trying to do here? (in a single query)

推荐答案

使用以下代码，您可以将其表示为: yield(用户，image.maybe)

With the code below you can put it like: yield (user, image.maybe)

case class RemoteImage(id: Long, url: URL)

class RemoteImages extends Table[RemoteImage]("RemoteImage") {
    def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
    def url = column[URL]("url", O.NotNull)
    def * = id.? ~ url <> (RemoteImage.apply _, RemoteImage.unapply _)

    def maybe = id.? ~ url.? <> (applyMaybe,unapplyBlank)

    val unapplyBlank = (c:Option[RemoteImage])=>None        

    val applyMaybe = (t: (Option[Long],Option[URL])) => t match {
        case (Some(id),Some(url)) => Some(RemoteImage(Some(id),url))
        case _ => None
    } 
}

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