Best way to sum in associations?

[Alex Jonsson]

Hey! I've got two Ecto models like this:

defmodule Parent do
  schema "parents" do
    field :name, :string
    field :is_test, :boolean

    has_many :children, Child

    timestamps
  end
end

defmodule Child do
  schema "children" do
    field :count, :float
    field :value, :float

    belongs_to :parent, Parent

    timestamps
  end
end

When I list the Parents, I want to be able to show the total sum of the "value" properties if its' children. Which is the most efficient way to query this using Ecto?

Thanks!

Alex

[José Valim]

If you are using Ecto 2.0-rc: parent |> assoc(:children) |> Repo.aggregate(:sum)

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José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

[Alex Jonsson]

Thanks José! Actually I realised that Enum.sum worked just fine since I already populated the children. But the aggregate function was new to me and amazing for another use case :)

Great work,

Alex

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