Variable query support (#177)

* Frontend (#168)
* #168 Sample data
* #168 label mapping
* #168 Backend
* Fixed tests
---------

Co-authored-by: Vyacheslav Mitrofanov <[email protected]>

.gitignore

@@ -9,3 +9,6 @@ vendor
 coverage
 .idea
 .vscode
+
+# OS generated files
+.DS_Store

README.md

@@ -23,12 +23,12 @@ To see the datasource in action, please follow the [Quick Demo](https://github.c
 * Query configurator
 * Raw CQL query editor
 * Table mode
+* Variables
 * Annotations
 * Alerting
 
 **Contacts**:
 
-* [![Discord Chat](https://img.shields.io/badge/discord-chat%20with%20us-green)](https://discord.gg/FU2Cb4KTyp) 
 * [![Github discussions](https://img.shields.io/badge/github-discussions-green)](https://github.com/HadesArchitect/GrafanaCassandraDatasource/discussions)
 
 **TOC**
@@ -45,7 +45,7 @@ To see the datasource in action, please follow the [Quick Demo](https://github.c
 
 You can find more detailed instructions in [the datasource wiki](https://github.com/HadesArchitect/GrafanaCassandraDatasource/wiki).
 
-### Installation 
+### Installation
 
 1. Install the plugin using grafana console tool: `grafana-cli plugins install hadesarchitect-cassandra-datasource`. The plugin will be installed into your grafana plugins directory; the default is `/var/lib/grafana/plugins`. Alternatively, download the plugin using [latest release](https://github.com/HadesArchitect/GrafanaCassandraDatasource/releases/latest), please download `cassandra-datasource-VERSION.zip` and uncompress a file into the Grafana plugins directory (`grafana/plugins`).
 2. Add the Apache Cassandra Data Source as a data source at the datasource configuration page.
@@ -162,6 +162,9 @@ PER PARTITION LIMIT 1
 ```
 Note that `PER PARTITION LIMIT 1` used instead of `LIMIT 1` to query one row for each partition and not just one row total.
 
+### Variables
+[Grafana Variables documentation](https://grafana.com/docs/grafana/latest/dashboards/variables/)
+
 ### Annotations
 [Grafana Annotations documentation](https://grafana.com/docs/grafana/latest/dashboards/build-dashboards/annotate-visualizations/)
 

backend/handler/handler.go

@@ -19,6 +19,7 @@ type ds interface {
 	GetKeyspaces(ctx context.Context) ([]string, error)
 	GetTables(keyspace string) ([]string, error)
 	GetColumns(keyspace, table, needType string) ([]string, error)
+	GetVariables(ctx context.Context, query string) ([]plugin.Variable, error)
 	CheckHealth(ctx context.Context) error
 	Dispose()
 }
@@ -37,6 +38,7 @@ func New(fn datasource.InstanceFactoryFunc) datasource.ServeOpts {
 	mux.HandleFunc("/keyspaces", h.getKeyspaces)
 	mux.HandleFunc("/tables", h.getTables)
 	mux.HandleFunc("/columns", h.getColumns)
+	mux.HandleFunc("/variables", h.getVariables)
 
 	// QueryDataHandler
 	queryTypeMux := datasource.NewQueryTypeMux()
@@ -153,6 +155,30 @@ func (h *handler) getColumns(rw http.ResponseWriter, req *http.Request) {
 	writeHTTPResult(rw, columns)
 }
 
+// getVariables is a handle to fetch variable values.
+func (h *handler) getVariables(rw http.ResponseWriter, req *http.Request) {
+	backend.Logger.Debug("Process 'variables' request")
+
+	pluginCtx := httpadapter.PluginConfigFromContext(req.Context())
+	p, err := h.getPluginInstance(req.Context(), pluginCtx)
+	if err != nil {
+		backend.Logger.Error("Failed to get plugin instance", "Message", err)
+		rw.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
+	query := req.URL.Query().Get("query")
+
+	variables, err := p.GetVariables(req.Context(), query)
+	if err != nil {
+		backend.Logger.Error("Failed to get variables", "Message", err)
+		rw.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
+	writeHTTPResult(rw, variables)
+}
+
 // getPluginInstance fetches plugin instance from instance manager, then
 // returns it if it has been successfully asserted that it is a plugin type.
 func (h *handler) getPluginInstance(ctx context.Context, pluginCtx backend.PluginContext) (ds, error) {
@@ -194,10 +220,9 @@ func (h *handler) CheckHealth(ctx context.Context, req *backend.CheckHealthReque
 	}, nil
 }
 
-// writeHTTPResult is a simple helper to serialize the
-// list of strings and put it in a http response.
-func writeHTTPResult(rw http.ResponseWriter, list []string) {
-	jsonBytes, err := json.MarshalIndent(list, "", "    ")
+// writeHTTPResult is a simple helper to serialize data and put it in a http response.
+func writeHTTPResult(rw http.ResponseWriter, val any) {
+	jsonBytes, err := json.MarshalIndent(val, "", "    ")
 	if err != nil {
 		backend.Logger.Error("Failed to marshal list", "Message", err)
 		rw.WriteHeader(http.StatusInternalServerError)

backend/handler/handler_test.go

@@ -32,6 +32,7 @@ type pluginMock struct {
 	onGetKeyspaces func(ctx context.Context) ([]string, error)
 	onGetTables    func(keyspace string) ([]string, error)
 	onGetColumns   func(keyspace, table, needType string) ([]string, error)
+	onGetVariables func(ctx context.Context, query string) ([]plugin.Variable, error)
 	onCheckHealth  func(ctx context.Context) error
 	onDispose      func()
 }
@@ -52,6 +53,10 @@ func (p *pluginMock) GetColumns(keyspace, table, needType string) ([]string, err
 	return p.onGetColumns(keyspace, table, needType)
 }
 
+func (p *pluginMock) GetVariables(ctx context.Context, query string) ([]plugin.Variable, error) {
+	return p.onGetVariables(ctx, query)
+}
+
 func (p *pluginMock) CheckHealth(ctx context.Context) error {
 	return p.onCheckHealth(ctx)
 }
@@ -228,7 +233,7 @@ func Test_CheckHealth(t *testing.T) {
 func Test_writeHTTPResult(t *testing.T) {
 	testCases := []struct {
 		name   string
-		input  []string
+		input  any
 		status int
 		want   string
 	}{
@@ -260,6 +265,29 @@ func Test_writeHTTPResult(t *testing.T) {
     "ONE",
     "TWO",
     "THREE"
+]`,
+		},
+		{
+			name: "variables",
+			input: []plugin.Variable{
+				{Value: "value1", Label: "text1"},
+				{Value: "value2", Label: "text2"},
+				{Value: "value3", Label: "text3"},
+			},
+			status: http.StatusOK,
+			want: `[
+    {
+        "value": "value1",
+        "text": "text1"
+    },
+    {
+        "value": "value2",
+        "text": "text2"
+    },
+    {
+        "value": "value3",
+        "text": "text3"
+    }
 ]`,
 		},
 	}

backend/main.go

@@ -19,7 +19,7 @@ func newDataSource(settings backend.DataSourceInstanceSettings) (instancemgmt.In
 	err := json.Unmarshal(settings.JSONData, &dss)
 	if err != nil {
 		backend.Logger.Error("Failed to parse connection parameter", "Message", err)
-		return nil, fmt.Errorf("failed to parse connection parameters: %w", err)
+		return nil, fmt.Errorf("Failed to parse connection parameters: %w", err)
 	}
 
 	var tlsConfig *tls.Config
@@ -29,7 +29,7 @@ func newDataSource(settings backend.DataSourceInstanceSettings) (instancemgmt.In
 		tlsConfig, err = prepareTLSCfg(dss.CertPath, dss.RootPath, dss.CaPath, dss.AllowInsecureTLS)
 		if err != nil {
 			backend.Logger.Error("Failed to create TLS config", "Message", err)
-			return nil, fmt.Errorf("failed to create TLS config: %w", err)
+			return nil, fmt.Errorf("Failed to create TLS config: %w", err)
 		}
 	}
 
@@ -46,7 +46,7 @@ func newDataSource(settings backend.DataSourceInstanceSettings) (instancemgmt.In
 	session, err := cassandra.New(sessionSettings)
 	if err != nil {
 		backend.Logger.Error("Failed to create Cassandra connection", "Message", err)
-		return nil, fmt.Errorf("failed to create Cassandra connection, check Grafana logs for more details")
+		return nil, fmt.Errorf("Failed to create Cassandra connection, check Grafana logs for more details")
 	}
 
 	return plugin.New(session), nil

backend/plugin/plugin.go

@@ -97,14 +97,34 @@ func (p *Plugin) GetTables(keyspace string) ([]string, error) {
 	return tables, nil
 }
 
-// GetColumns fetches and returns Cassandra's list of columns of given type for provided keyspace and table.
+// GetColumns fetches and returns Cassandra's list of columns
+// of given type for provided keyspace and table.
 func (p *Plugin) GetColumns(keyspace, table, needType string) ([]string, error) {
-	tables, err := p.repo.GetColumns(keyspace, table, needType)
+	columns, err := p.repo.GetColumns(keyspace, table, needType)
 	if err != nil {
 		return nil, fmt.Errorf("repo.GetColumns: %w", err)
 	}
 
-	return tables, nil
+	return columns, nil
+}
+
+// GetVariables fetches and returns data to create variables.
+func (p *Plugin) GetVariables(ctx context.Context, query string) ([]Variable, error) {
+	backend.Logger.Debug("GetVariables", "query", query)
+
+	idRows, err := p.repo.Select(ctx, query)
+	if err != nil {
+		return nil, fmt.Errorf("repo.Select: %w", err)
+	}
+
+	vars := make([]Variable, 0, len(idRows))
+	for _, rows := range idRows {
+		for _, row := range rows {
+			vars = append(vars, makeVariableFromRow(row))
+		}
+	}
+
+	return vars, nil
 }
 
 // CheckHealth executes repository Ping method to check database health.
@@ -272,3 +292,22 @@ func removeNonTSFields(frame *data.Frame) *data.Frame {
 
 	return frame
 }
+
+// Variable is a type to transfer variable data from backend to frontend,
+// where it will be put into MetricFindValue type.
+// https://github.com/grafana/grafana/blob/main/packages/grafana-data/src/types/datasource.ts#L595
+type Variable struct {
+	Value string `json:"value"`
+	Label string `json:"text"`
+}
+
+func makeVariableFromRow(row cassandra.Row) Variable {
+	var v Variable
+	v.Value = fmt.Sprintf("%v", row.Fields[row.Columns[0]])
+	v.Label = v.Value
+	if len(row.Columns) > 1 {
+		v.Label = fmt.Sprintf("%v", row.Fields[row.Columns[1]])
+	}
+
+	return v
+}

backend/plugin/plugin_test.go

@@ -193,6 +193,78 @@ func TestPlugin_ExecQuery(t *testing.T) {
 	}
 }
 
+func TestPlugin_GetVariables(t *testing.T) {
+	testCases := []struct {
+		name string
+		repo *repositoryMock
+		want []Variable
+	}{
+		{
+			name: "response with labels",
+			repo: &repositoryMock{
+				onSelect: func(ctx context.Context, query string, values ...interface{}) (rows map[string][]cassandra.Row, err error) {
+					return map[string][]cassandra.Row{
+						"1": {
+							{
+								Columns: []string{"Value", "Label"},
+								Fields:  map[string]interface{}{"Value": "1", "Label": "Text1"},
+							},
+						},
+						"2": {
+							{
+								Columns: []string{"Value", "Label"},
+								Fields:  map[string]interface{}{"Value": "2", "Label": "Text2"},
+							},
+						},
+					}, nil
+				},
+			},
+			want: []Variable{
+				{Value: "1", Label: "Text1"},
+				{Value: "2", Label: "Text2"},
+			},
+		},
+		{
+			name: "response without labels",
+			repo: &repositoryMock{
+				onSelect: func(ctx context.Context, query string, values ...interface{}) (rows map[string][]cassandra.Row, err error) {
+					return map[string][]cassandra.Row{
+						"1": {
+							{
+								Columns: []string{"Value"},
+								Fields:  map[string]interface{}{"Value": "1"},
+							},
+						},
+						"2": {
+							{
+								Columns: []string{"Value"},
+								Fields:  map[string]interface{}{"Value": "2"},
+							},
+						},
+					}, nil
+				},
+			},
+			want: []Variable{
+				{Value: "1", Label: "1"},
+				{Value: "2", Label: "2"},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			p := &Plugin{repo: tc.repo}
+			vars, err := p.GetVariables(context.TODO(), "SELECT * FROM keyspace.table")
+			assert.NoError(t, err)
+
+			sort.Slice(vars, func(i, j int) bool {
+				return vars[i].Value < vars[j].Value
+			})
+			assert.Equal(t, tc.want, vars)
+		})
+	}
+}
+
 func Test_makeDataFrameFromRows(t *testing.T) {
 	testCases := []struct {
 		name  string