There is a really interesting Hex package named lens (or on github) which allows to easily perform manipulations of deeply nested maps.
Below you’ll find two examples. The first updates user_id without any context (key of current map value) and the second has the context to allow updating user_id with the value of the key (0 or 1). Lens.into/2 is used to reconstruct a map out of the list we get from Lens.all/0.
iex(1)> m = %{
...(1)> "zip" => "",
...(1)> "location" => "",
...(1)> "user_sports" => %{
...(1)> "0" => %{"sport_id" => "1", "user_id" => ""},
...(1)> "1" => %{"sport_id" => "1", "user_id" => ""},
...(1)> },
...(1)> }
%{
"location" => "",
"user_sports" => %{
"0" => %{"sport_id" => "1", "user_id" => ""},
"1" => %{"sport_id" => "1", "user_id" => ""}
},
"zip" => ""
}
iex(2)> lens1 = Lens.key("user_sports") |> Lens.map_values() |> Lens.key("user_id")
#Function<41.112152499/3 in Lens.seq/2>
iex(3)> Lens.map(lens1, m, fn _v -> "updated" end)
%{
"location" => "",
"user_sports" => %{
"0" => %{"sport_id" => "1", "user_id" => "updated"},
"1" => %{"sport_id" => "1", "user_id" => "updated"}
},
"zip" => ""
}
iex(4)> lens2 = Lens.key("user_sports") |> Lens.into(Lens.context(Lens.all(), Lens.at(1) |> Lens.key("user_id")), %{})
#Function<41.112152499/3 in Lens.seq/2>
iex(5)> Lens.map(lens2, m, fn {{id, _map}, _v} -> "updated with #{id}" end)
%{
"location" => "",
"user_sports" => %{
"0" => %{"sport_id" => "1", "user_id" => "updated with 0"},
"1" => %{"sport_id" => "1", "user_id" => "updated with 1"}
},
"zip" => ""
}