Slick:通过获取列名查询多个表/数据库 [英] Slick: query multiple tables/databases with getting column names

问题描述

我的 Play 应用程序中有一些方法可以查询超过一百列的数据库表.我无法为每个这样的查询定义案例类，因为它会大得离谱，并且必须随着数据库表的每次更改而更改.

I have methods in my Play app that query database tables with over hundred columns. I can't define case class for each such query, because it would be just ridiculously big and would have to be changed with each alter of the table on the database.

我正在使用这种方法，查询结果如下所示:

I'm using this approach, where result of the query looks like this:

Map(columnName1 -> columnVal1, columnName2 -> columnVal2, ...)

代码示例:

implicit val getListStringResult = GetResult[List[Any]] (
    r => (1 to r.numColumns).map(_ => r.nextObject).toList
)

def getSomething(): Map[String, Any] = DB.withSession {
    val columns = MTable.getTables(None, None, None, None).list.filter(_.name.name == "myTable").head.getColumns.list.map(_.column) 
    val result = sql"""SELECT * FROM myTable LIMIT 1""".as[List[Any]].firstOption.map(columns zip _ toMap).get
}

当查询仅在单个数据库和单个表上运行时，这不是问题.我需要能够在我的查询中使用多个表和数据库，如下所示:

This is not a problem when query only runs on a single database and single table. I need to be able to use multiple tables and databases in my query like this:

def getSomething(): Map[String, Any] = DB.withSession {

    //The line below is no longer valid because of multiple tables/databases
    val columns = MTable.getTables(None, None, None, None).list.filter(_.name.name == "table1").head.getColumns.list.map(_.column) 
    val result = sql"""
        SELECT      * 
        FROM        db1.table1
        LEFT JOIN   db2.table2 ON db2.table2.col1 = db1.table1.col1
        LIMIT       1
    """.as[List[Any]].firstOption.map(columns zip _ toMap).get

}

不能再使用相同的方法来检索列名.使用 PHP PDO 或 Java JDBCTemplate 之类的东西时不存在此问题 - 这些无需任何额外工作即可检索列名.

The same approach can no longer be used to retrieve column names. This problem doesn't exist when using something like PHP PDO or Java JDBCTemplate - these retrieve column names without any extra effort needed.

我的问题是:如何使用 Slick 实现这一目标?

My question is: how do I achieve this with Slick?

推荐答案

import scala.slick.jdbc.{GetResult,PositionedResult}
object ResultMap extends GetResult[Map[String,Any]] {
  def apply(pr: PositionedResult) = {
    val rs = pr.rs // <- jdbc result set
    val md = rs.getMetaData();
    val res = (1 to pr.numColumns).map{ i=> md.getColumnName(i) -> rs.getObject(i) }.toMap
    pr.nextRow // <- use Slick's advance method to avoid endless loop
    res
  }
}
val result = sql"select * from ...".as(ResultMap).firstOption

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