光滑-可选地包括/省略大列

问题描述

假设我有一个表，其中包含许多小列和一个大列(例如BLOB):

Suppose I have a table with a number of small columns, and a large (say BLOB) column:

  case class Thing(id: Int, small1: String, small2: String, small3: String, large: String)

  class ThingMapping(tag: Tag) extends Table[Thing](tag, "things") {

    def id = column[Int]("id", O.PrimaryKey, O.NotNull, O.AutoInc)
    def small1 = column[String]("small1")
    def small2 = column[String]("small2")
    def small3 = column[String]("small3")
    def large = column[String]("large")

    def * = (id, small1, small2, small3, large) <> (Thing.tupled, Thing.unapply)

  }

在某些情况下，我想查询表中除large列以外的所有列.在其他情况下，我想将其包括在内.我更喜欢使用案例类而不是元组.

Under some circumstances, I'd like to query the table for all the columns except the large column. In others, I'd like to include it. I prefer to use case classes rather than tuples.

Slick中是否有执行此操作的良好模式?

Is there good pattern in Slick for doing this?

我考虑过的选项:

1. 具有两个映射-瘦"和胖"映射.
2. 将大列拆分为单独的表，然后根据需要将其加入.

推荐答案

我认为您需要的是TableQuery上的map函数，以允许您仅选择字段的子集.像这样:

I think what you need here is the map function on your TableQuery to allow you to select only a subset of fields. So something like this:

case class Thing(id: Int, small1: String, small2: String, small3: String, large: String)
case class LiteThing(id: Int, small1: String, small2: String, small3: String)
class ThingMapping(tag: Tag) extends Table[Thing](tag, "things") {
  def id = column[Int]("id", O.PrimaryKey, O.NotNull, O.AutoInc)
  def small1 = column[String]("small1")
  def small2 = column[String]("small2")
  def small3 = column[String]("small3")
  def large = column[String]("large")
  def * = (id, small1, small2, small3, large) <> (Thing.tupled, Thing.unapply)
}
val things = TableQuery[ThingMapping]

val liteThingQuery = things.map(t => LiteThing(t.id, t.small1, t.small2, t.small3))

因此，我添加了另一个名为LiteThing的案例类，它表示字段的子集，但不包括large列.然后，我使用map创建一个新查询，该查询不会选择该large字段，它映射到LiteThing.我没有对此进行编译，但是我很确定这是您要进入的方向.我是从 Hello Slick激活器模板，在选择特定的列"部分中(完全扩展了教程信息之后).

So I added another case class called LiteThing that represents the subset of fields, excluding the large column. I then use map to create a new query that will not select that large field and it maps to a LiteThing. I have no compiled this, but I'm pretty sure this is the direction you want to go in. I got this from the Hello Slick Activator Template, in the section "Selecting Specific Columns" (after fully expanding the tutorial info).

您可以尝试使用类似的替代方法

You can play around with alternatives like

def small = (id, small1, small2, small3)
def * = (small, large)

或

def small = (id, small1, small2, small3)
def * = small ~ large <> (Thing.tupled, Thing.unapply)

并使用

things.map(_.small)

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