Ecto not allowing string interpolation in fragments?

Questions / Help
22

I had a similar issue trying to dynamically build fragment strings (from a trusted source) and it seems like a general escape hatch for these kind of issues, when trying to use third party macros with dynamic inputs where not explicitly supported is to use Code.eval_quoted. So, for example, you can wrap an entire select statement and fool Elixir/Ecto into thinking the variables are in fact literals:

Code.eval_quoted(
      quote do
        select(unquote(escaped_q), [table], %{
          dynamic_select: fragment(unquote(some_var), table.field))
        })
      end
    )

I am pretty positive this is the last tool you should reach for and maybe it would be better to use postgrex directly for these cases. I haven’t tried that so I can’t speak to the pros/cons but I’d love to hear people’s thoughts about the practice, and maybe whether Ecto could adopt some “blessed” way of circumventing protections like this one because I certainly feel dirty doing this.

2 Likes