Elixir map check if not empty and key exists

elixir phoenix-framework ecto
Pratik Khadloya picture Pratik Khadloya · Oct 24, 2015 · Viewed 16k times · Source

I am trying to figure out a way to check if the params hash in a Phoenix app (using Elixir) has a particular key or not.

In the below changeset function in a model, the params is defaulted to :empty. 

def changeset(model, params \\ :empty) do

I need to figure out if a key named :username exists in the hash.

Answer

Gazler picture Gazler · Oct 24, 2015

Just a small terminology thing, params is a map and not a hash. This is relevant when knowing where to look in the documentation.

For a map there is has_key?/2 which returns true or false.

Map.has_key?(params, :name)

Since you are using an Ecto changeset then you can also use Ecto.Changeset.get_change/3.

get_change(changeset, key, default \\ nil)

This returns default if key is not set. Please note that if key is set to nil then nil will still be returned. If nil is a permitted value for your change then you may want to set a different default parameter.

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