Question

在我在应用程序中的一个查询中，我刚刚意识到Slick在select中添加了这个add case语句。

以下是我构建查询的方法：

def search(searchCriteria: SearchCriteria,
             drop: Long = 0,
             take: Long = 100): Future[Seq[(School, Option[Address])]] = {
    val query = Schools.schools joinLeft
      Addresses.addresses on ((s, a) => s.addressId === a.id && a.deletedAt.isEmpty)

    val q = for {
      (school, address) <- query.filter{ case (s, a) =>
        List(
          Some(s.deletedAt.isEmpty),
          searchCriteria.school.name.map(n => s.name.toLowerCase like s"%${n.toLowerCase}%"),
          searchCriteria.school.ready.map(r => s.ready === r)
        ).collect({ case Some(criteria) => criteria }).reduceLeftOption(_ && _).getOrElse(true: Rep[Boolean])
      }
    } yield (school, address)

    db.run(q.drop(drop).take(take).result)
  }

这是一个非常简单的连接，有一些过滤。事实上，一切正常。但是，当我检查执行的查询时，我看到了：

SELECT
  x2."id",
  x2."address_id",
  x2."name",
  x2."about",
  x2."number_of_students",
  x2."website_url",
  x2."media_id",
  x2."slug",
  x2."short_description",
  x2."ready",
  x2."classrooms",
  x2."year_established",
  x2."display_copyright",
  x2."createdat",
  x2."updatedat",
  x2."deletedat",
  x2."createdby",
  x2."updatedby",
  x2."dli_number",
  (CASE WHEN (x3."id" IS NULL)
    THEN NULL
   ELSE 1 END),
  x3."id",
  x3."country_id",
  x3."continent_id",
  x3."state_id",
  x3."address1",
  x3."address2",
  x3."city",
  x3."zip",
  x3."createdat",
  x3."updatedat",
  x3."deletedat",
  x3."createdby",
  x3."updatedby"
FROM "school" x2 LEFT OUTER JOIN "address" x3 ON (x2."address_id" = x3."id") AND (x3."deletedat" IS NULL)
WHERE ((x2."deletedat" IS NULL) AND (lower(x2."name") LIKE '%a%')) AND (x2."ready" = TRUE)
LIMIT 100
OFFSET 0

为什么Slick添加了这个： (CASE WHEN (x3."id" IS NULL) THEN NULL ELSE 1 END)

我无法以任何方式看到这有用。

谢谢，

Slick：使用左连接创建查询时出现奇怪的case语句

0 个答案: