Identity: Add endpoint to get display info for an identifier (#91828)

pkg/storage/legacysql/README.md

@@ -0,0 +1,8 @@
+# Legacy SQL
+
+As we transition from our internal sql store towards unified storage, we can sometimes use existing
+services to implement a k8s compatible storage that can then dual write into unified storage.
+
+However sometimes it is more efficient and cleaner to write explicit SQL commands designed for this goal.
+
+This package provides some helper functions to make this easier.

pkg/storage/legacysql/rv.go

@@ -0,0 +1,51 @@
+package legacysql
+
+import (
+	"context"
+	"time"
+
+	"github.com/grafana/grafana/pkg/infra/db"
+	"github.com/grafana/grafana/pkg/services/sqlstore/migrator"
+)
+
+// The database may depend on the request context
+type NamespacedDBProvider func(ctx context.Context) (db.DB, error)
+
+// Get the list RV from the maximum updated time
+type ResourceVersionLookup = func(ctx context.Context) (int64, error)
+
+// Get a resource version from the max value the updated field
+func GetResourceVersionLookup(sql NamespacedDBProvider, table string, column string) ResourceVersionLookup {
+	return func(ctx context.Context) (int64, error) {
+		db, err := sql(ctx)
+		if err != nil {
+			return 1, err
+		}
+
+		table = db.GetDialect().Quote(table)
+		column = db.GetDialect().Quote(column)
+		switch db.GetDBType() {
+		case migrator.Postgres:
+			max := time.Now()
+			err := db.GetSqlxSession().Get(ctx, &max, "SELECT MAX("+column+") FROM "+table)
+			if err != nil {
+				return 1, nil
+			}
+			return max.UnixMilli(), nil
+		case migrator.MySQL:
+			max := int64(1)
+			_ = db.GetSqlxSession().Get(ctx, &max, "SELECT UNIX_TIMESTAMP(MAX("+column+")) FROM "+table)
+			return max, nil
+		default:
+			// fallthrough to string version
+		}
+
+		max := ""
+		err = db.GetSqlxSession().Get(ctx, &max, "SELECT MAX("+column+") FROM "+table)
+		if err == nil && max != "" {
+			t, _ := time.Parse(time.DateTime, max) // ignore null errors
+			return t.UnixMilli(), nil
+		}
+		return 1, nil
+	}
+}