Add example of getting only the association as a map (#3293)

elixir-ecto · May 6, 2020 · 1bb17e5 · 1bb17e5
1 parent 5614c30
commit 1bb17e5
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/lib/ecto/query/api.ex b/lib/ecto/query/api.ex
@@ -431,6 431,12 @@ defmodule Ecto.Query.API do
  from(city in City, preload: :country,
  select: map(city, [:country_id, :name, country: [:id, :population]]))
 
  It's also possible to select a struct from one source but only a subset of
  fields from one of its associations:
 
  from(city in City, preload: :country,
  select: %{city | country: map(country: [:id, :population]))
 
  **IMPORTANT**: When filtering fields for associations, you
  MUST include the foreign keys used in the relationship,
  otherwise Ecto will be unable to find associated records.