I have a dynamic query engine which is also handling search functionality. I have managed to make it dynamic in the sense that I pass the search fields as a list of atoms and up until now I was handling only single tables. Now I have a join of three tables and I ideally I want to be able to search in all of them by being more specific in the search fields that I pass.

Here is the function that until now worked for single tables:

search_fields=[ :description, :price]

defp single_table_search(query, search_term, search_fields) do

    or_conditions =
      Enum.reduce(search_fields, nil, fn field, dynamic_acc ->
        condition =
          if field in [:id, :serial_number] do
            dynamic(
              [s],
              ilike(fragment("CAST(? AS text)", field(s, ^field)), ^"%#{search_term}%")
            )
          else
            dynamic([s], ilike(field(s, ^field), ^"%#{search_term}%"))
          end

        if dynamic_acc do
          dynamic([s], ^dynamic_acc or ^condition)
        else
          condition
        end
      end)

    query |> where(^or_conditions)
  end

Now I have a join between 3 tables and ideally I want to pass to the search fields by specifiyng in which table and which columns I want to search on like that for example:

search_fields = [{:device, :name},  {:device_alarm, :level}]

 defp joined_table_search(query, _schema, search_term, search_fields) do
    binding_names = Enum.map(search_fields, fn {binding_name, _field_atom} -> binding_name end)
    IO.inspect(binding_names, label: "BINDING NAMES")
    or_conditions =
      Enum.reduce(search_fields, nil, fn {binding_name, field_atom}, dynamic_acc ->
        IO.inspect(binding_name, label: "BINDING NAME")
        IO.inspect(field_atom, label: "FIELD ATOM")
        condition =
          if field_atom in [:id, :serial_number] do
            dynamic(
              [binding_names],
              ilike(
                fragment("CAST(? AS text)", field(^binding_name, ^field_atom)),
                ^"%#{search_term}%"
              )
            )
          else
            dynamic(
              [binding_names],
              ilike(field(^binding_name, ^field_atom), ^"%#{search_term}%") #Error on this line
            )
          end

        if dynamic_acc do
          dynamic([], ^dynamic_acc or ^condition)
        else
          condition
        end
      end)

    query
    |> where(^or_conditions)
  end

but this gives me a compilation error on the first else condition about the field atom:

** (Protocol.UndefinedError) protocol String.Chars not implemented for {:^, [line: 186, column: 42], [{:field_atom, [line: 186, column: 43], nil}]} of type Tuple
    (elixir 1.16.0) lib/string/chars.ex:3: String.Chars.impl_for!/1
    (elixir 1.16.0) lib/string/chars.ex:22: String.Chars.to_string/1
    (ecto 3.11.2) lib/ecto/query/builder.ex:642: Ecto.Query.Builder.escape_field!/3
    (ecto 3.11.2) lib/ecto/query/builder.ex:88: Ecto.Query.Builder.escape/5
    (elixir 1.16.0) lib/enum.ex:1826: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
    (ecto 3.11.2) lib/ecto/query/builder.ex:618: Ecto.Query.Builder.escape_call/5
    (ecto 3.11.2) lib/ecto/query/builder/dynamic.ex:15: Ecto.Query.Builder.Dynamic.build/3
    (ecto 3.11.2) expanding macro: Ecto.Query.dynamic/2

Which is really strange as this should’t be a tuple. I removed that part of the code just to be able to compile and inspect the values and I get

BINDING NAMES: [:device, :device_alarm]
BINDING NAME: :device
FIELD ATOM: :name
BINDING NAME: :device_alarm
FIELD ATOM: :level

What am I doing wrong or is this a bug?