Handle Param wihich may/may not have key

Questions & Help Questions
,
1

I am getting params that may/may not have the key. For example here is my params

params: %{"job_opening_id" => job_opening_id, "stage_id" => stage_id}

Sometimes, my params only contain job_opening_id and sometimes both. How can make pattern matching that accepts both types of params?

2

You can’t. Pattern matches are meant to ensure the given data fulfills the pattern given. If you have optional data either use multiple patterns/functions or extract the data in the functions body using e.g. Map.get.

3

Aren`t they two different methods matching any of the cases?

4

You can define a function that matches a map having both keys, and afterwards one that matches a partial map and calls the previous after putting defaults:

def foo(%{"param1" => param1, "param2" => param2}) do
end

def foo(params) when is_map(params) do
  params
  |> Map.put_new("param1", default_param1)
  # as many as needed
  |> foo()
end
5

This sounds like a quite complex way of doing params = Map.merge(defaults, params).

6

If you don’t want to use another function head then do something like this:

def foo(%{"job_opening_id" => job_opening_id} = params) do
  # stage_id will be either nil or have a value
  stage_id = params["stage_id"]

  ...
end

You can test for nil via if or case and do something depending on weather stage_id has a value.