将光滑的查询组合到单个查询中

Question

使用Slick 3.1,如何将多个查询组合成同一类型的单个查询？这不是连接或联合,而是组合查询"段"以创建单个查询请求.这些"段"可以是任何单独有效的查询.

val query = TableQuery[SomeThingValid]

// build up pieces of the query in various parts of the application logic
val q1 = query.filter(_.value > 10)
val q2 = query.filter(_.value < 40)
val q3 = query.sortBy(_.date.desc)
val q4 = query.take(5)

// how to combine these into a single query ?
val finalQ = ??? q1 q2 q3 q4 ???

// in order to run in a single request
val result = DB.connection.run(finalQ.result)

编辑:预期的SQL应该是这样的:

SELECT * FROM "SomeThingValid" WHERE "SomeThingValid"."value" > 10 AND "SomeThingValid"."valid" < 40 ORDER BY "MemberFeedItem"."date" DESC LIMIT 5

Answer 1

val q1 = query.filter(_.value > 10)
val q2 = q1.filter(_.value < 40)
val q3 = q2.sortBy(_.date.desc)
val q4 = q3.take(5)

我认为你应该做上面的事情(并传递Querys),但如果你坚持传递查询"段",这样的事情可以工作:

type QuerySegment = Query[SomeThingValid, SomeThingValid, Seq] => Query[SomeThingValid, SomeThingValid, Seq]

val q1: QuerySegment = _.filter(_.value > 10)
val q2: QuerySegment = _.filter(_.value < 40)
val q3: QuerySegment = _.sortBy(_.date.desc)
val q4: QuerySegment = _.take(5)

val finalQ = Function.chain(Seq(q1, q2, q3, q4))(query)