From 4e68e5e2cee7c6a0c00dd9d5e78ab90087e0a2ba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Santiago=20Hern=C3=A1ndez?=
 <santiagohernandez.1997@gmail.com>
Date: Fri, 12 Dec 2025 15:05:29 +0100
Subject: [PATCH] Alerting: Add compact model for alert rules

---
 pkg/services/ngalert/store/compat.go      | 38 ++++++++++++++++++++---
 pkg/services/ngalert/store/compat_test.go | 12 +++++++
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/pkg/services/ngalert/store/compat.go b/pkg/services/ngalert/store/compat.go
index 4f4194facc1..cb076bbd763 100644
--- a/pkg/services/ngalert/store/compat.go
+++ b/pkg/services/ngalert/store/compat.go
@@ -10,11 +10,38 @@ import (
 	"github.com/grafana/grafana/pkg/services/ngalert/models"
 )
 
+// We only care about the data source UIDs.
+type compactQuery struct {
+	DatasourceUID string `json:"datasourceUid"`
+}
+
 func alertRuleToModelsAlertRule(ar alertRule, l log.Logger) (models.AlertRule, error) {
+	return transformRule(ar, l, false)
+}
+
+// alertRuleToModelsAlertRuleCompact transforms an alertRule to a models.AlertRule
+// ignoring alert queries (except for data source UIDs), notification settings, and metadata.
+func alertRuleToModelsAlertRuleCompact(ar alertRule, l log.Logger) (models.AlertRule, error) {
+	return transformRule(ar, l, true)
+}
+
+// transformRule creates a models.AlertRule from an alertRule.
+// When 'compact' is set to 'true', it skips parsing the alert queries (except for the data source UID), notification
+// settings, and metadata, thus reducing the number of JSON serializations needed.
+func transformRule(ar alertRule, l log.Logger, compact bool) (models.AlertRule, error) {
 	var data []models.AlertQuery
-	err := json.Unmarshal([]byte(ar.Data), &data)
-	if err != nil {
-		return models.AlertRule{}, fmt.Errorf("failed to parse data: %w", err)
+	if compact {
+		var cqs []compactQuery
+		if err := json.Unmarshal([]byte(ar.Data), &cqs); err != nil {
+			return models.AlertRule{}, fmt.Errorf("failed to parse data: %w", err)
+		}
+		for _, cq := range cqs {
+			data = append(data, models.AlertQuery{DatasourceUID: cq.DatasourceUID})
+		}
+	} else {
+		if err := json.Unmarshal([]byte(ar.Data), &data); err != nil {
+			return models.AlertRule{}, fmt.Errorf("failed to parse data: %w", err)
+		}
 	}
 
 	result := models.AlertRule{
@@ -52,6 +79,7 @@ func alertRuleToModelsAlertRule(ar alertRule, l log.Logger) (models.AlertRule, e
 		result.UpdatedBy = util.Pointer(models.UserUID(*ar.UpdatedBy))
 	}
 
+	var err error
 	if ar.NoDataState != "" {
 		result.NoDataState, err = models.NoDataStateFromString(ar.NoDataState)
 		if err != nil {
@@ -90,7 +118,7 @@ func alertRuleToModelsAlertRule(ar alertRule, l log.Logger) (models.AlertRule, e
 		}
 	}
 
-	if ar.NotificationSettings != "" {
+	if !compact && ar.NotificationSettings != "" {
 		ns, err := parseNotificationSettings(ar.NotificationSettings)
 		if err != nil {
 			return models.AlertRule{}, fmt.Errorf("failed to parse notification settings: %w", err)
@@ -98,7 +126,7 @@ func alertRuleToModelsAlertRule(ar alertRule, l log.Logger) (models.AlertRule, e
 		result.NotificationSettings = ns
 	}
 
-	if ar.Metadata != "" {
+	if !compact && ar.Metadata != "" {
 		err = json.Unmarshal([]byte(ar.Metadata), &result.Metadata)
 		if err != nil {
 			return models.AlertRule{}, fmt.Errorf("failed to metadata: %w", err)
diff --git a/pkg/services/ngalert/store/compat_test.go b/pkg/services/ngalert/store/compat_test.go
index 990ec5dd3e1..4f7b4f41f3f 100644
--- a/pkg/services/ngalert/store/compat_test.go
+++ b/pkg/services/ngalert/store/compat_test.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/infra/log/logtest"
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
 	"github.com/grafana/grafana/pkg/util"
@@ -81,3 +82,14 @@ func TestAlertRuleVersionToAlertRule(t *testing.T) {
 		}
 	})
 }
+
+func BenchmarkAlertRuleToModelsAlertRule(b *testing.B) {
+	r := ngmodels.RuleGen.Generate()
+	ar, err := alertRuleFromModelsAlertRule(r)
+	require.NoError(b, err)
+	l := log.NewNopLogger()
+
+	for range b.N {
+		alertRuleToModelsAlertRuleCompact(ar, l)
+	}
+}