CODEWITHSUNDEEP
elixir
hnhl
hnhl

Reputation: 137

elixir map.put not updating map

I have a function that has a Map %{} as its param

def set_data (data) do
...
end

I am trying to update the param data using map.put.

data is a flat map like so

%{
 a: ...
 b: ...
 c: ...
}

What I have an issue with is setting a key/property in the data map with another map that looks like this:

ModuleA.EctoSchemaMap{
 some_key: nil,
 another_key: ModuleB.EctoSchemaMap{
  inner_key_a: "456",
  inner_key_b: nil
 }
}

This map above ModuleA.EctoSchemaMap is returned from a function call like so

some_data = get_data()

So some_data = ModuleA.EctoSchemaMap map above.

For some reason, when I try to update the key b in the param data map in the function, everything will copy over that is a nil value in the ModuleA.EctoSchemaMap map, but the key inner_key_a shows as nil as well, even though before some_data shows inner_key_a is not nil

data
|> map.put(:a, "123")
|> map.put(:b, some_data)

After doing the piping above, I was expecting data to have :b updated with the value

b: ModuleA.EctoSchemaMap{
    some_key: nil,
    another_key: ModuleB.EctoSchemaMap{
     inner_key_a: "456", //I need this value to be there
     inner_key_b: nil
    }
   }

but it is instead showing this

b: ModuleA.EctoSchemaMap{
    some_key: nil,
    another_key: ModuleB.EctoSchemaMap{
     inner_key_a: nil, //NOT sure why this is being set as nil even though `some_data` had a value for this
     inner_key_b: nil
    }
   }

Upvotes: 0

Views: 651

Answers (1)

Shivam Singla
Shivam Singla

Reputation: 2201

All the data structures are immuatable in Elixir. In the code, Map.put creates a new copy of the map with your given key-value added/updated. But it is not storing anywhere. So, reassigne the variable data_map

data_map = data_map
|> map.put(:some_key, data)

Since your have only one operation in the pipe, the recommended way to it is-

data_map = Map.put(data_map, :some_key, data)

Also note that it is Map not map.

Upvotes: 4

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