Add Carte champs support to the API

app/serializers/champs/carte_champ_serializer.rb

@@ -0,0 +1,11 @@
+class Champs::CarteChampSerializer < ChampSerializer
+  has_many :geo_areas
+
+  def value
+    if object.value.present?
+      JSON.parse(object.value)
+    else
+      nil
+    end
+  end
+end

app/serializers/geo_area_serializer.rb

@@ -0,0 +1,16 @@
+class GeoAreaSerializer < ActiveModel::Serializer
+  attributes :geometry,
+    :source,
+    :surface_intersection,
+    :surface_parcelle,
+    :numero,
+    :feuille,
+    :section,
+    :code_dep,
+    :nom_com,
+    :code_com,
+    :code_arr,
+    :code,
+    :nom,
+    :commune
+end

spec/factories/geo_area.rb

@@ -0,0 +1,7 @@
+FactoryBot.define do
+  factory :geo_area do
+    source { GeoArea.sources.fetch(:cadastre) }
+    numero { '42' }
+    feuille { 'A11' }
+  end
+end

spec/serializers/champs/carte_champ_serializer_spec.rb

@@ -0,0 +1,18 @@
+describe Champs::CarteChampSerializer do
+  describe '#attributes' do
+    subject { Champs::CarteChampSerializer.new(champ).serializable_hash }
+
+    context 'when type champ is carte' do
+      let(:geo_area) { create(:geo_area) }
+      let(:champ) { create(:type_de_champ_carte).champ.create(geo_areas: [geo_area]) }
+
+      it {
+        expect(subject[:geo_areas].first).to include(
+          source: GeoArea.sources.fetch(:cadastre),
+          numero: '42',
+          feuille: 'A11'
+        )
+      }
+    end
+  end
+end