Slick 2.0:删除多行 [英] Slick 2.0: Delete multiple rows

问题描述

我想要做的是使用此功能从表中删除N个最早的ID:

What I wanted to do is delete the N oldest ids from my table using this function:

def deleteOldRows(size: Int)(implicit s: Session): Int =
  MyTable.sortBy(_.id.asc).take(size).delete

此操作将抛出SlickException，因为

对DELETE语句的查询必须解析为具有单个表的理解-不支持的形状:Comprehension(fetch = None，offset = None)

A query for a DELETE statement must resolve to a comprehension with a single table -- Unsupported shape: Comprehension(fetch = None, offset = None)

如文档中所述:

用于删除的查询只能从单个表中选择.任何投影都会被忽略(它总是删除整行).

A query for deleting must only select from a single table. Any projection is ignored (it always deletes full rows).

什么触发了多重表?是因为sortBy子句创建了一个临时表来存储结果吗?目前，我将查询重写为:

What is triggering the multiple table? Is it because the sortBy clause creates a temporary table to store the results? For the moment I rewrote my query to this:

MyTable.sortBy(_.id.asc).take(size).list().map(result => MyTable.filter(_.id === result.id).delete)

基本上是哪个ID，对于每个过滤器并删除它们，是否有一种更具可读性和直接性的方式即可一次删除多行?

Which is basically take the ids and for each one filter and delete, is there a more readable and direct way to delete multiple rows at once?

推荐答案

尝试MyTable.filter(_.id in MyTable.sortBy(_.id.asc).take(size).map(_.id)).delete.暂时不查看详细信息，我假设错误消息具有误导性，并且DELETE不支持原因ORDER BY和LIMIT.

Try MyTable.filter(_.id in MyTable.sortBy(_.id.asc).take(size).map(_.id)).delete. Without looking at the details right now, I am assuming the error message to be misleading and the cause to be ORDER BY and LIMIT to not be supported for DELETE.

我创建了一张票证: https://github.com/slick/slick/issues/872

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