api/ds/query: simplify data sources lookup for queries and expressions (#41172)

pkg/expr/service.go

@@ -4,21 +4,34 @@ import (
 	"context"
 
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana/pkg/components/simplejson"
+	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/plugins"
 	"github.com/grafana/grafana/pkg/setting"
 )
 
-// DatasourceName is the string constant used as the datasource name in requests
-// to identify it as an expression command.
-const DatasourceName = "__expr__"
+// DatasourceType is the string constant used as the datasource when the property is in Datasource.Type.
+// Type in requests is used to identify what type of data source plugin the request belongs to.
+const DatasourceType = "__expr__"
+
+// DatasourceUID is the string constant used as the datasource name in requests
+// to identify it as an expression command when use in Datasource.UID.
+const DatasourceUID = DatasourceType
 
 // DatasourceID is the fake datasource id used in requests to identify it as an
 // expression command.
 const DatasourceID = -100
 
-// DatasourceUID is the fake datasource uid used in requests to identify it as an
-// expression command.
-const DatasourceUID = "-100"
+// OldDatasourceUID is the datasource uid used in requests to identify it as an
+// expression command. It goes with the query root level datasourceUID property. It was accidentally
+// set to the Id and is now kept for backwards compatibility. The newer Datasource.UID property
+// should be used instead and should be set to "__expr__".
+const OldDatasourceUID = "-100"
+
+// IsDataSource checks if the uid points to an expression query
+func IsDataSource(uid string) bool {
+	return uid == DatasourceUID || uid == OldDatasourceUID
+}
 
 // Service is service representation for expression handling.
 type Service struct {
@@ -52,3 +65,14 @@ func (s *Service) ExecutePipeline(ctx context.Context, pipeline DataPipeline) (*
 	}
 	return res, nil
 }
+
+func DataSourceModel() *models.DataSource {
+	return &models.DataSource{
+		Id:             DatasourceID,
+		Uid:            DatasourceUID,
+		Name:           DatasourceUID,
+		Type:           DatasourceType,
+		JsonData:       simplejson.New(),
+		SecureJsonData: make(map[string][]byte),
+	}
+}