Composing an Ecto query with multiple columns in a where clause joined by OR

Question

Let's say I have this query:

User
|> where([u], u.name == "John" or u.age == 24)

I want to turn this into a function that can take a keyword list of field names and field values and dynamically generate this same query. The function definition would look something like this:

def where_any(query, field_names_to_values) do
  ...
end

Is this possible with Elixir and Ecto?

I do this sort of composability in a library of mine with macros as @jisaacstone suggests. See github.com/rcdilorenzo/filtrex/blob/master/test/ast_test.exs for an example. — Christian Di Lorenzo

jisaacstone jisaacstone · Accepted Answer · 2016-01-27T05:16:42

Wouldn't normally advocate a macro, but ecto does so much complex magic I think it's best in this case to keep the abstract syntax tree intact.

defmacro any_expr(var, [{key, value} | rest]) do
  Enum.reduce(
    rest,
    quote do unquote(var).unquote(key) == unquote(value) end,
    fn ({k, v}, acc) ->
      quote do: unquote(acc) or unquote(var).unquote(k) == unquote(v)
    end)
end

should work like this:

User
|> where([u], any_expr(u, [name: "John", age: 24]))

(note that this is untested code...)

Composing an Ecto query with multiple columns in a where clause joined by OR

1 Answers