1 files changed, 107 insertions, 0 deletions
diff --git a/app/models/concerns/optimized_issuable_label_filter.rb b/app/models/concerns/optimized_issuable_label_filter.rb
new file mode 100644
index 00000000000..7be4a26d4fa
--- /dev/null
+++ b/app/models/concerns/optimized_issuable_label_filter.rb
@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+module OptimizedIssuableLabelFilter
+  def by_label(items)
+    return items unless params.labels?
+
+    return super if Feature.disabled?(:optimized_issuable_label_filter)
+
+    target_model = items.model
+
+    if params.filter_by_no_label?
+      items.where('NOT EXISTS (?)', optimized_any_label_query(target_model))
+    elsif params.filter_by_any_label?
+      items.where('EXISTS (?)', optimized_any_label_query(target_model))
+    else
+      issuables_with_selected_labels(items, target_model)
+    end
+  end
+
+  # Taken from IssuableFinder
+  def count_by_state
+    return super if root_namespace.nil?
+    return super if Feature.disabled?(:optimized_issuable_label_filter)
+
+    count_params = params.merge(state: nil, sort: nil, force_cte: true)
+    finder = self.class.new(current_user, count_params)
+
+    state_counts = finder
+      .execute
+      .reorder(nil)
+      .group(:state_id)
+      .count
+
+    counts = state_counts.transform_keys { |key| count_key(key) }
+
+    counts[:all] = counts.values.sum
+    counts.with_indifferent_access
+  end
+
+  private
+
+  def issuables_with_selected_labels(items, target_model)
+    if root_namespace
+      all_label_ids = find_label_ids(root_namespace)
+      # Found less labels in the DB than we were searching for. Return nothing.
+      return items.none if all_label_ids.size != params.label_names.size
+
+      all_label_ids.each do |label_ids|
+        items = items.where('EXISTS (?)', optimized_label_query_by_label_ids(target_model, label_ids))
+      end
+    else
+      params.label_names.each do |label_name|
+        items = items.where('EXISTS (?)', optimized_label_query_by_label_name(target_model, label_name))
+      end
+    end
+
+    items
+  end
+
+  def find_label_ids(root_namespace)
+    finder_params = {
+      include_subgroups: true,
+      include_ancestor_groups: true,
+      include_descendant_groups: true,
+      group: root_namespace,
+      title: params.label_names
+    }
+
+    LabelsFinder
+      .new(nil, finder_params)
+      .execute(skip_authorization: true)
+      .pluck(:title, :id)
+      .group_by(&:first)
+      .values
+      .map { |labels| labels.map(&:last) }
+  end
+
+  def root_namespace
+    strong_memoize(:root_namespace) do
+      (params.project || params.group)&.root_ancestor
+    end
+  end
+
+  def optimized_any_label_query(target_model)
+    LabelLink
+      .where(target_type: target_model.name)
+      .where(LabelLink.arel_table['target_id'].eq(target_model.arel_table['id']))
+      .limit(1)
+  end
+
+  def optimized_label_query_by_label_ids(target_model, label_ids)
+    LabelLink
+      .where(target_type: target_model.name)
+      .where(LabelLink.arel_table['target_id'].eq(target_model.arel_table['id']))
+      .where(label_id: label_ids)
+      .limit(1)
+  end
+
+  def optimized_label_query_by_label_name(target_model, label_name)
+    LabelLink
+      .joins(:label)
+      .where(target_type: target_model.name)
+      .where(LabelLink.arel_table['target_id'].eq(target_model.arel_table['id']))
+      .where(labels: { name: label_name })
+      .limit(1)
+  end
+end