bus: support multiple dispatch in one transaction

this makes it possible to run multiple DispatchCtx
in one transaction. The TransactionManager will
start/end the transaction and pass the dbsession
in the context.Context variable

pkg/services/sqlstore/stats.go

@@ -1,6 +1,7 @@
 package sqlstore
 
 import (
+	"context"
 	"time"
 
 	"github.com/grafana/grafana/pkg/bus"
@@ -13,6 +14,7 @@ func init() {
 	bus.AddHandler("sql", GetDataSourceAccessStats)
 	bus.AddHandler("sql", GetAdminStats)
 	bus.AddHandler("sql", GetSystemUserCountStats)
+	bus.AddCtxHandler("sql", GetSystemUserCountStatsCtx)
 }
 
 var activeUserTimeLimit = time.Hour * 24 * 30
@@ -133,6 +135,22 @@ func GetAdminStats(query *m.GetAdminStatsQuery) error {
 	return err
 }
 
+func GetSystemUserCountStatsCtx(ctx context.Context, query *m.GetSystemUserCountStatsQuery) error {
+	return withDbSession(ctx, func(sess *DBSession) error {
+
+		var rawSql = `SELECT COUNT(id) AS Count FROM ` + dialect.Quote("user")
+		var stats m.SystemUserCountStats
+		_, err := sess.SQL(rawSql).Get(&stats)
+		if err != nil {
+			return err
+		}
+
+		query.Result = &stats
+
+		return err
+	})
+}
+
 func GetSystemUserCountStats(query *m.GetSystemUserCountStatsQuery) error {
 	var rawSql = `SELECT COUNT(id) AS Count FROM ` + dialect.Quote("user")
 	var stats m.SystemUserCountStats