feat: Ability to select DocumentIds (#16)

* feat: Ability to select DocumentIds

closes #14

README.md

@@ -78,6 +78,7 @@ select * from users order by 'address.city' desc limit 10
 select * from `users` where id > 50
 select id, LENGTH(contacts) as total_contacts from `users`
 select id, (age > 100) as centenarian as total_contacts from `users`
+select __name__ from users // to select document id
 ```
 
 `FireQL` depend on [govaluate](https://github.com/Knetic/govaluate) to evaluate expressions in `SELECT`. See list of possible expressions and operators [here](https://github.com/Knetic/govaluate/blob/master/MANUAL.md#operators). 

pkg/select/select.go

@@ -88,7 +88,7 @@ func (sel *SelectStatement) Execute() (*util.QueryResult, error) {
 
 func (sel *SelectStatement) readResults(docs *firestore.DocumentIterator, selectedColumns []*selectColumn) (*util.QueryResult, error) {
 	document, err := docs.Next()
-	if err == iterator.Done {
+	if errors.Is(err, iterator.Done) {
 		var columns []string
 		for _, column := range selectedColumns {
 			columns = append(columns, column.alias)
@@ -147,7 +147,7 @@ func (sel *SelectStatement) readResults(docs *firestore.DocumentIterator, select
 			row[idx] = val
 		}
 		document, err = docs.Next()
-		if err == iterator.Done {
+		if errors.Is(err, iterator.Done) {
 			break
 		}
 	}
@@ -159,16 +159,20 @@ func readColumnValue(document *firestore.DocumentSnapshot, data *map[string]inte
 	var val interface{}
 	switch column.colType {
 	case Field:
-		fieldPaths := strings.Split(column.field, ".")
-		var colData interface{}
-		colData = *data
-		for _, fPath := range fieldPaths {
-			colData = colData.(map[string]interface{})[fPath]
-			if colData == nil {
-				return nil, fmt.Errorf(`unknown field "%s" in doc "%s"`, column.field, document.Ref.ID)
+		if column.field == firestore.DocumentID {
+			val = document.Ref.ID
+		} else {
+			fieldPaths := strings.Split(column.field, ".")
+			var colData interface{}
+			colData = *data
+			for _, fPath := range fieldPaths {
+				colData = colData.(map[string]interface{})[fPath]
+				if colData == nil {
+					return nil, fmt.Errorf(`unknown field "%s" in doc "%s"`, column.field, document.Ref.ID)
+				}
 			}
+			val = colData
 		}
-		val = colData
 		break
 	case Function:
 		params := make([]interface{}, len(column.params))

pkg/select/select_test.go

@@ -95,6 +95,12 @@ var selectTests = []TestExpect{
 		length:  "1",
 		records: [][]interface{}{[]interface{}{true}},
 	},
+	TestExpect{
+		query:   "select __name__ from users where id = 1",
+		columns: []string{"__name__"},
+		length:  "1",
+		records: [][]interface{}{[]interface{}{"1"}},
+	},
 }
 
 func newFirestoreTestClient(ctx context.Context) *firestore.Client {