Method Schema

runtime/metricsview/executor/executor.go:273–332

Schema returns a schema for the metrics view's dimensions and measures.

(ctx context.Context)

// Schema returns a schema for the metrics view's dimensions and measures.
func (e *Executor) Schema(ctx context.Context) (*runtimev1.StructType, error) {
	if !e.security.CanAccess() {
		return nil, runtime.ErrForbidden
	}

	// Build a query that selects all dimensions and measures.
	//
	// NOTE: We don't give special treatment to time dimensions here because:
	// 1. if we use TimeFloor on a time idmension, it might its actual type (e.g. from DATE to TIMESTAMP or vice versa),
	// 2. we may not know all the time dimensions yet (that inference happens later based on the result from this query).
	qry := &metricsview.Query{}

	for _, d := range e.metricsView.Dimensions {
		if e.security.CanAccessField(d.Name) {
			qry.Dimensions = append(qry.Dimensions, metricsview.Dimension{Name: d.Name})
		}
	}

	for _, m := range e.metricsView.Measures {
		if e.security.CanAccessField(m.Name) {
			qry.Measures = append(qry.Measures, metricsview.Measure{Name: m.Name})
		}
	}

	// Setting both base and comparison time ranges in case there are time_comparison measures.
	// Do not set it for BigQuery because it requires datatype to be already discovered to set time parameter.
	if e.olap.Dialect().String() != drivers.DialectNameBigQuery && e.metricsView.TimeDimension != "" {
		now := time.Now()
		qry.TimeRange = &metricsview.TimeRange{
			Start: now.Add(-time.Second),
			End:   now,
		}
		qry.ComparisonTimeRange = &metricsview.TimeRange{
			Start: now.Add(-2 * time.Second),
			End:   now.Add(-time.Second),
		}
	}

	// Importantly, limit to 0 rows
	zero := int64(0)
	qry.Limit = &zero

	// Execute the query to get the schema
	ast, err := metricsview.NewAST(e.metricsView, e.security, qry, e.olap.Dialect())
	if err != nil {
		return nil, err
	}

	sql, args, err := ast.SQL()
	if err != nil {
		return nil, err
	}

	schema, err := e.olap.QuerySchema(ctx, sql, args)
	if err != nil {
		return nil, err
	}