查询的RESULTSET的隐式转换 [英] implicit conversion of RESULTSET for queries

问题描述

我正在使用Scala 2.10，并且在Slick上遇到问题(普通查询，java.sql.ResultSet).如果我写

这样的查询

Q.query[String, ResultSet](query).list(rs.getString("id"))

日食会告诉我could not find implicit value for parameter rconv: scala.slick.jdbc.GetResult[java.sql.ResultSet]

此问题的最重要来源( http://slick.typesafe. com/doc/0.11.2/sql.html )没有帮助.如何编写这些隐式转换?还有其他其他熟悉的方式来表示Slick中的ResultSet吗?

解决方案

让我尝试阐明一下:).如果有ResultSet，则应具有实际将结果集映射到的类型.例如.将保留您的行的元组或案例类.如果是自定义(案例)类，则必须提供一个implicit GetResult来描述如何从jdbc ResultSet映射到您的类. .list的参数应该是您希望Slick放在准备好的语句的占位符中的值，而不是您得到的ResultSet的值(假设这就是rs的意思).

建议的用法如下:

import scala.slick.jdbc.{GetResult, StaticQuery}
import StaticQuery.interpolation

val price = 1000.0

// use tuples
val expensiveDevices: List[Device] =
  Q.query[String, (Long,Double,Date)]("select * from DEVICE where PRICE > ?").list( price )

// or a case class (needs implicit GetResult for Device)
case class Device(id: Long,price: Double,acquisition: Date)
implicit val getDeviceResult =
  GetResult(r => Device(r.<<, r.<<, r.<<))
val expensiveDevices2: List[Device] =
  Q.query[String, Device]("select * from DEVICE where PRICE > ?").list( price )

// or the even nicer interpolation syntax
val expensiveDevices3: List[Device] =
  sql"select * from DEVICE where PRICE > $price"    .as[Device].list

I'm using Scala 2.10 and have problems with Slick (plain queries, java.sql.ResultSet). If I write queries like

Q.query[String, ResultSet](query).list(rs.getString("id"))

eclipse will tell me could not find implicit value for parameter rconv: scala.slick.jdbc.GetResult[java.sql.ResultSet]

My most important source for this issue ( http://slick.typesafe.com/doc/0.11.2/sql.html ) does not help. How do I write these implicit conversions? And is there any other, familar way of representing ResultSets in Slick?

解决方案

Let's me try to shed some light :). Where you have ResultSet, you should have a type you actually map result sets to. E.g. a tuple or a case class that will hold your row. In case of a custom (case) class you will have to provide an implicit GetResult that describes how to map from a jdbc ResultSet to your class. The argument to .list should be a value that you want Slick to put in the placeholder of your prepared statement, not something that you get our of a ResultSet (assuming that that is what rs stands for).

The suggested use is something like this:

import scala.slick.jdbc.{GetResult, StaticQuery}
import StaticQuery.interpolation

val price = 1000.0

// use tuples
val expensiveDevices: List[Device] =
  Q.query[String, (Long,Double,Date)]("select * from DEVICE where PRICE > ?").list( price )

// or a case class (needs implicit GetResult for Device)
case class Device(id: Long,price: Double,acquisition: Date)
implicit val getDeviceResult =
  GetResult(r => Device(r.<<, r.<<, r.<<))
val expensiveDevices2: List[Device] =
  Q.query[String, Device]("select * from DEVICE where PRICE > ?").list( price )

// or the even nicer interpolation syntax
val expensiveDevices3: List[Device] =
  sql"select * from DEVICE where PRICE > $price"    .as[Device].list

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