Key Error in Livebook

Postgrex.query! returns a single Postgrex.Result value, you’ll need to extract the data from the result’s rows and columns.

Thanks for the reply.

Yes. I can call result.rows and get returned a map of maps with all the values. I can call result.columns and get a map of column (field) names as strings.

What I want to do is pass a map of the values of a column into another function (the “id” column, or the “geom” column. How do I access that value?

I think I am missing something basic in elixir… but if I try
result.rows.id I get a key error.

Thinking the issue was the keys are strings, not atoms, I tried result.rows["id"]and received the following error:

** (ArgumentError) the Access module supports only keyword lists (with atom keys), got "id"

What am I missing?

Thanks again for the help.
Regards
DJ

Okay, so I solve my particular issue. I merged teh column and row values into a map and then worked with that.

Here is the function that did that if anyone else is interested:

stn_map = Enum.map(result.rows, fn row ->
  result.columns
  |> Enum.zip(row)
  # |> Map.new()
  |> Map.new(fn {k, v} -> {String.to_atom(k), v} end)
end)

Thanks again for all help.
DJ

Neither of those things are maps.

• rows is a list of lists of mixed types
• columns is a list of binaries

A simple way to get something closer to what you want might be:

Enum.map(result.rows, fn row ->
  result.columns
  |> Enum.zip(result.columns, row)
  |> Map.new()
end)

This will give you a list of maps with string keys. HOWEVER, the results may not be what you expect if result.columns has duplicate names (since a Map can only have one value for a key).

Alternatively, consider a library like Ecto that has already taken care of details llke this.

cross reply … I was working on that this morning.

Thanks again, al2o3cr

DJ

You can also use Table.to_rows(stations) to convert the result to list of maps : )