Allow to modify the query FillMode (#27)

Author: andresmgot

datasource.go

@@ -92,11 +92,17 @@ func (ds *sqldatasource) handleQuery(req backend.DataQuery) (data.Frames, error)
 		return nil, errors.WithMessage(err, "Could not apply macros")
 	}
 
+	// Apply the default FillMode, overwritting it if the query specifies it
+	fillMode := ds.c.FillMode()
+	if q.FillMissing != nil {
+		fillMode = q.FillMissing
+	}
+
 	// FIXES:
 	//  * Some datasources (snowflake) expire connections or have an authentication token that expires if not used in 1 or 4 hours.
 	//    Because the datasource driver does not include an option for permanent connections, we retry the connection
 	//    if the query fails. NOTE: this does not include some errors like "ErrNoRows"
-	res, err := query(ds.db, ds.c.Converters(), ds.c.FillMode(), q)
+	res, err := query(ds.db, ds.c.Converters(), fillMode, q)
 	if err == nil {
 		return res, nil
 	}
@@ -106,7 +112,7 @@ func (ds *sqldatasource) handleQuery(req backend.DataQuery) (data.Frames, error)
 		if err != nil {
 			return nil, err
 		}
-		return query(ds.db, ds.c.Converters(), ds.c.FillMode(), q)
+		return query(ds.db, ds.c.Converters(), fillMode, q)
 	}
 
 	return nil, err

query.go

@@ -32,6 +32,7 @@ type Query struct {
 	Interval      time.Duration     `json:"-"`
 	TimeRange     backend.TimeRange `json:"-"`
 	MaxDataPoints int64             `json:"-"`
+	FillMissing   *data.FillMissing `json:"fillMode,omitempty"`
 
 	// Macros
 	Schema string `json:"schema,omitempty"`
@@ -48,6 +49,7 @@ func (q *Query) WithSQL(query string) *Query {
 		Interval:      q.Interval,
 		TimeRange:     q.TimeRange,
 		MaxDataPoints: q.MaxDataPoints,
+		FillMissing:   q.FillMissing,
 		Schema:        q.Schema,
 		Table:         q.Table,
 		Column:        q.Column,
@@ -70,6 +72,7 @@ func GetQuery(query backend.DataQuery) (*Query, error) {
 		Interval:      query.Interval,
 		TimeRange:     query.TimeRange,
 		MaxDataPoints: query.MaxDataPoints,
+		FillMissing:   model.FillMissing,
 		Schema:        model.Schema,
 		Table:         model.Table,
 		Column:        model.Column,