perf(graphql): improuve dossier loading

app/graphql/connections/dossiers_connection.rb

@@ -0,0 +1,23 @@
+module Connections
+  class DossiersConnection < GraphQL::Pagination::ActiveRecordRelationConnection
+    def initialize(items, lookahead: nil, **kwargs)
+      super(items, **kwargs)
+      @lookahead = lookahead
+    end
+
+    def nodes
+      if @nodes.nil? && preload?
+        DossierPreloader.new(super).all
+      else
+        super
+      end
+    end
+
+    private
+
+    # We check if the query selects champs form dossier. If it's the case we preload the dossier.
+    def preload?
+      @lookahead.selection(:nodes).selects?(:champs) || @lookahead.selection(:nodes).selects?(:annotations)
+    end
+  end
+end

app/graphql/types/champs/repetition_champ_type.rb

@@ -5,7 +5,11 @@ module Types::Champs
     field :champs, [Types::ChampType], null: false
 
     def champs
-      Loaders::Association.for(object.class, :champs).load(object)
+      if object.champs.loaded?
+        object.champs
+      else
+        Loaders::Association.for(object.class, :champs).load(object)
+      end
     end
   end
 end

app/graphql/types/demarche_type.rb

@@ -32,7 +32,7 @@ module Types
     field :groupe_instructeurs, [Types::GroupeInstructeurType], null: false
     field :service, Types::ServiceType, null: true
 
-    field :dossiers, Types::DossierType.connection_type, "Liste de tous les dossiers d’une démarche.", null: false do
+    field :dossiers, Types::DossierType.connection_type, "Liste de tous les dossiers d’une démarche.", null: false, extras: [:lookahead] do
       argument :order, Types::Order, default_value: :asc, required: false, description: "L’ordre des dossiers."
       argument :created_since, GraphQL::Types::ISO8601DateTime, required: false, description: "Dossiers déposés depuis la date."
       argument :updated_since, GraphQL::Types::ISO8601DateTime, required: false, description: "Dossiers mis à jour depuis la date."
@@ -72,7 +72,7 @@ module Types
       Loaders::Association.for(object.class, :revisions).load(object)
     end
 
-    def dossiers(updated_since: nil, created_since: nil, state: nil, archived: nil, revision: nil, max_revision: nil, min_revision: nil, order:)
+    def dossiers(updated_since: nil, created_since: nil, state: nil, archived: nil, revision: nil, max_revision: nil, min_revision: nil, order:, lookahead:)
       dossiers = object
         .dossiers
         .visible_by_administration
@@ -108,7 +108,11 @@ module Types
         dossiers = dossiers.order_by_created_at(order)
       end
 
-      dossiers
+      # We wrap dossiers in a custom connection alongsite the lookahead for the query.
+      # The custom connection is responsible for preloading paginated dossiers.
+      # https://graphql-ruby.org/pagination/custom_connections.html#using-a-custom-connection
+      # https://graphql-ruby.org/queries/lookahead.html
+      Connections::DossiersConnection.new(dossiers, lookahead: lookahead)
     end
 
     def deleted_dossiers(deleted_since: nil, order:)

app/graphql/types/dossier_type.rb

@@ -120,6 +120,8 @@ module Types
         Loaders::Champ
           .for(object, private: false)
           .load(ApplicationRecord.id_from_typed_id(id))
+      elsif object.champs.loaded?
+        object.champs
       else
         Loaders::Association.for(object.class, champs: :type_de_champ).load(object)
       end
@@ -130,6 +132,8 @@ module Types
         Loaders::Champ
           .for(object, private: true)
           .load(ApplicationRecord.id_from_typed_id(id))
+      elsif object.champs_private.loaded?
+        object.champs_private
       else
         Loaders::Association.for(object.class, champs_private: :type_de_champ).load(object)
       end

app/models/dossier_preloader.rb

@@ -11,6 +11,12 @@ class DossierPreloader
     dossiers
   end
 
+  def all
+    dossiers = @dossiers.to_a
+    load_dossiers(dossiers)
+    dossiers
+  end
+
   private
 
   # returns: { revision_id : { type_de_champ_id : position } }