小编san*_*omf的帖子

我正在使用 doobie 查询一些数据，一切正常，如下所示：

case class Usuario(var documento: String, var nombre: String, var contrasena: String)

  def getUsuario(doc: String) =
     sql"""SELECT documento, nombre, contrasena FROM "Usuario" WHERE "documento" = $doc"""
      .query[Usuario]
      .option
      .transact(xa)
      .unsafeRunSync()

但是，如果我声明一个具有类型限制的函数，如下所示：

 def getOption[T](f: Fragment): Option[T] = {
    f.query[T]
     .option
     .transact(xa)
     .unsafeRunSync()

}

我收到了这些错误：

Error:(42, 12) Cannot find or construct a Read instance for type:
  T
This can happen for a few reasons, but the most common case is that a data
member somewhere within this type doesn't have …