review: query the db only once

app/models/dossier.rb

@@ -1229,10 +1229,10 @@ class Dossier < ApplicationRecord
     cloned_dossier
   end
 
-  def find_champ_by_stable_id(stable_id)
-    return nil if stable_id.blank?
+  def find_champs_by_stable_ids(stable_ids)
+    return [] if stable_ids.compact.empty?
 
-    champs_public.joins(:type_de_champ).find_by(types_de_champ: { stable_id: stable_id })
+    champs_public.joins(:type_de_champ).where(types_de_champ: { stable_id: stable_ids })
   end
 
   private

app/models/prefill_params.rb

@@ -5,15 +5,47 @@ class PrefillParams
   end
 
   def to_a
-    @params
-      .to_unsafe_hash
-      .map { |key, value| PrefillValue.new(@dossier, key, value) }
+    # Builds: [{ stable_id: 1, value: "a value" }, { stable_id: 2, value: "another value"}]
+    stable_ids_and_values = convert_typed_ids_to_stable_ids
+
+    # Builds: [{stable_id: "1", champ: #<Champs::...>}, {stable_id: "2", champ: #<Champs::...>}]
+    stable_ids_and_champs = find_champs(stable_ids_and_values.map { _1[:stable_id] })
+
+    # Merges the arrays together, filters out the values we don't want and returns [{ id: champ_1_id, value: value_1}, ...]
+    merge_by_stable_ids(stable_ids_and_values + stable_ids_and_champs)
+      .map { PrefillValue.new(champ: _1[:champ], value: _1[:value]) }
       .filter(&:prefillable?)
       .map(&:to_h)
   end
 
   private
 
+  def convert_typed_ids_to_stable_ids
+    @params
+      .to_unsafe_hash
+      .map { |typed_id, value| { stable_id: stable_id_from_typed_id(typed_id), value: value } }
+      .filter { _1[:stable_id].present? && _1[:value].present? }
+  end
+
+  def find_champs(stable_ids)
+    @dossier
+      .find_champs_by_stable_ids(stable_ids)
+      .map { |champ| { stable_id: champ.stable_id.to_s, champ: champ } }
+  end
+
+  def merge_by_stable_ids(arrays_of_hashes_with_stable_id)
+    arrays_of_hashes_with_stable_id
+      .group_by { _1[:stable_id] }
+      .values
+      .map { _1.reduce(:merge) }
+  end
+
+  def stable_id_from_typed_id(typed_id)
+    Champ.id_from_typed_id(typed_id)
+  rescue
+    nil
+  end
+
   class PrefillValue
     AUTHORIZED_TYPES_DE_CHAMPS = [
       TypeDeChamp.type_champs.fetch(:text),
@@ -39,8 +71,8 @@ class PrefillParams
 
     attr_reader :champ, :value
 
-    def initialize(dossier, typed_id, value)
-      @champ = find_champ(dossier, typed_id)
+    def initialize(champ:, value:)
+      @champ = champ
       @value = value
     end
 
@@ -71,12 +103,5 @@ class PrefillParams
       champ.value = value
       champ.valid?
     end
-
-    def find_champ(dossier, typed_id)
-      stable_id = Champ.id_from_typed_id(typed_id) rescue nil
-      return unless stable_id
-
-      dossier.find_champ_by_stable_id(stable_id)
-    end
   end
 end