Question

这些是参数：

 %{
  "$select" => %{
    "$avg" => ["arrive_at"],
    "$count" => ["arrive_at"],
    "$fields" => ["id"],
    "$max" => ["cost"],
    "$min" => ["arrive_at"],
    "$sum" => ["arrive_at"]
  }
 }

这是代码：

 select when is_map(select) ->
        query = from(p in queryable, select: %{})

        fields =
          Enum.reduce(select, [], fn {key, value}, fields ->
            Enum.reduce(value, query, fn {k, v}, query ->
              case k do
                "$avg" ->
                  val = Enum.at(v, 0)

                  query =
                    from(
                      p in query,
                      select_merge: %{avg: avg(field(p, ^String.to_atom(val)))}
                    )

                "$count" ->
                  val = Enum.at(v, 0)

                  query =
                    from(
                      p in query,
                      select_merge: %{count: count(field(p, ^String.to_atom(val)))}
                    )

                "$min" ->
                  val = Enum.at(v, 0)

                  query =
                    from(
                      p in query,
                      select_merge: %{min: min(field(p, ^String.to_atom(val)))}
                    )

                "$max" ->
                  val = Enum.at(v, 0)

                  query =
                    from(
                      p in query,
                      select_merge: %{max: max(field(p, ^String.to_atom(val)))}
                    )

                "$sum" ->
                  val = Enum.at(v, 0)

                  query =
                    from(
                      p in query,
                      select_merge: %{sum: sum(field(p, ^String.to_atom(val)))}
                    )

                "$fields" ->
                  fields = Enum.at(v, 0)
                  IO.inspect(fields)
              end
            end)
           end)
         end

如果我在没有$fields语句的情况下运行此代码。它正确返回选择合并查询。

但如果我用$fields运行它。它给了我错误。

  (Protocol.UndefinedError) protocol Ecto.Queryable not implemented for [:id]

它将$fields的值作为我的模型名称并在查询中使用它

为什么它的表现如此？将$fields的值作为我的模型。

非常感谢任何帮助。

感谢。

Answer 1

您必须返回任何具有Ecto.Queryable实施（即https://docs.silverstripe.org/en/3.1/developer_guides/files/image/）的内容，并且您的代码目前正在返回List（fields。）忘记你在reduce 里面，返回的值是累加器。 FWIW，

"$fields" ->
  fields = Enum.at(v, 0)
  IO.inspect(fields)
  query   # ⇐ NOTE THE RETURNED VALUE

将作为存根工作，直到正确实现。

case语句在select merge中设置为model

1 个答案: