Use include ActiveModel::Model to hold metrics data parsed from yaml.

lib/gitlab/prometheus/additional_metrics_parser.rb

@@ -9,26 +9,17 @@ module Gitlab
       private
-      def metrics_from_list(list)
-        list.map { |entry| metric_from_entry(entry) }
-      end
-
-      def metric_from_entry(entry)
-        required_fields = [:title, :required_metrics, :weight, :queries]
-        missing_fields = required_fields.select { |key| entry[key].nil? }
-        raise ParsingError.new("entry missing required fields #{missing_fields}") unless missing_fields.empty?
-
-        Metric.new(entry[:title], entry[:required_metrics], entry[:weight], entry[:y_label], entry[:queries])
+      def validate!(obj)
+        raise ParsingError.new(obj.errors.full_messages.join('\n')) unless obj.valid?
       end
       def group_from_entry(entry)
-        required_fields = [:group, :priority, :metrics]
-        missing_fields = required_fields.select { |key| entry[key].nil? }
-
-        raise ParsingError.new("entry missing required fields #{missing_fields.map(&:to_s)}") unless missing_fields.empty?
-        group = MetricGroup.new(entry[:group], entry[:priority])
-        group.tap { |g| g.metrics = metrics_from_list(entry[:metrics]) }
+        entry[:name] = entry.delete(:group)
+        entry[:metrics]&.map! do |entry|
+          Metric.new(entry).tap(&method(:validate!))
+        end
+        MetricGroup.new(entry).tap(&method(:validate!))
       end
       def additional_metrics_raw

lib/gitlab/prometheus/metric.rb

 module Gitlab
   module Prometheus
     class Metric
-      attr_reader :group, :title, :required_metrics, :weight, :y_label, :queries
-      def initialize(title, required_metrics, weight, y_label, queries = [])
-        @title = title
-        @required_metrics = required_metrics
-        @weight = weight
-        @y_label = y_label || 'Values'
-        @queries = queries
+      include ActiveModel::Model
+      attr_accessor :title, :required_metrics, :weight, :y_label, :queries
+
+      validates :title, :required_metrics, :weight, :y_label, :queries, presence: true
+
+      def initialize(params = {})
+        super(params)
+        @y_label ||= 'Values'
       end
     end
   end

lib/gitlab/prometheus/metric_group.rb

 module Gitlab
   module Prometheus
     class MetricGroup
-      attr_reader :priority, :name
-      attr_accessor :metrics
-      def initialize(name, priority, metrics = [])
-        @name = name
-        @priority = priority
-        @metrics = metrics
-      end
+      include ActiveModel::Model
+      attr_accessor :name, :priority, :metrics
+      validates :name, :priority, :metrics, presence: true
       def self.all
         AdditionalMetricsParser.load_groups_from_yaml

spec/lib/gitlab/prometheus/additional_metrics_parser_spec.rb

@@ -26,7 +26,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
             priority: 1
             metrics: 
               - title: title
-                required_metrics: []
+                required_metrics: ['metric_a']
                 weight: 1
                 queries: [{query_range: query_range_a}]
         EOF
@@ -54,7 +54,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         expect(metrics.count).to eq(3)
         expect(metrics[0]).to have_attributes(title: 'title', required_metrics: %w(metric_a metric_b), weight: 1)
         expect(metrics[1]).to have_attributes(title: 'title', required_metrics: %w(metric_a), weight: 1)
-        expect(metrics[2]).to have_attributes(title: 'title', required_metrics: [], weight: 1)
+        expect(metrics[2]).to have_attributes(title: 'title', required_metrics: %w{metric_a}, weight: 1)
       end
       it 'provides query data' do
@@ -78,7 +78,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         end
         it 'throws parsing error' do
-          expect { subject }.to raise_error(parser_error_class, /missing.*#{field_name}/)
+          expect { subject }.to raise_error(parser_error_class, /#{field_name} can't be blank/i)
         end
       end
@@ -88,13 +88,13 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         end
         it 'throws parsing error' do
-          expect { subject }.to raise_error(parser_error_class, /missing.*#{field_name}/)
+          expect { subject }.to raise_error(parser_error_class, /#{field_name} can't be blank/i)
         end
       end
     end
     describe 'group required fields' do
-      it_behaves_like 'required field', :metrics do
+      it_behaves_like 'required field', 'metrics' do
         let(:field_nil) do
           <<-EOF.strip_heredoc
             - group: group_a
@@ -111,10 +111,11 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         end
       end
-      it_behaves_like 'required field', :group do
+      it_behaves_like 'required field', 'name' do
         let(:field_nil) do
           <<-EOF.strip_heredoc
-            - priority: 1
+            - group:
+              priority: 1
               metrics: []
           EOF
         end
@@ -127,7 +128,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         end
       end
-      it_behaves_like 'required field', :priority do
+      it_behaves_like 'required field', 'priority' do
         let(:field_nil) do
           <<-EOF.strip_heredoc
             - group: group_a
@@ -146,7 +147,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
     end
     describe 'metrics fields parsing' do
-      it_behaves_like 'required field', :title do
+      it_behaves_like 'required field', 'title' do
         let(:field_nil) do
           <<-EOF.strip_heredoc
             - group: group_a
@@ -171,7 +172,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         end
       end
-      it_behaves_like 'required field', :required_metrics do
+      it_behaves_like 'required field', 'required metrics' do
         let(:field_nil) do
           <<-EOF.strip_heredoc
             - group: group_a
@@ -196,7 +197,7 @@ describe Gitlab::Prometheus::AdditionalMetricsParser, lib: true do
         end
       end
-      it_behaves_like 'required field', :weight do
+      it_behaves_like 'required field', 'weight' do
         let(:field_nil) do
           <<-EOF.strip_heredoc
             - group: group_a

spec/support/prometheus/metric_builders.rb

@@ -9,7 +9,7 @@ module Prometheus
     end
     def simple_metric(title: 'title', required_metrics: [], queries: [simple_query])
-      Gitlab::Prometheus::Metric.new(title, required_metrics, 1, nil, queries)
+      Gitlab::Prometheus::Metric.new(title: title, required_metrics: required_metrics, weight: 1, queries: queries)
     end
     def simple_metrics(added_metric_name: 'metric_a')
@@ -21,7 +21,7 @@ module Prometheus
     end
     def simple_metric_group(name: 'name', metrics: simple_metrics)
-      Gitlab::Prometheus::MetricGroup.new( name, 1, metrics)
+      Gitlab::Prometheus::MetricGroup.new(name: name, priority: 1, metrics: metrics)
     end
   end
 end