linkedql: Allow no from in final steps

cayleygraph · Jan 18, 2020 · 5f8ddfe · 5f8ddfe
1 parent 87fbc46
commit 5f8ddfe
Show file tree

Hide file tree

Showing 2 changed files with 28 additions and 28 deletions.
diff --git a/query/linkedql/iter_docs.go b/query/linkedql/iter_docs.go
@@ -22,8 +22,7 @@ type DocumentIterator struct {
 }
 
 // NewDocumentIterator returns a new DocumentIterator for a QuadStore and Path.
-func NewDocumentIterator(valueIt *ValueIterator) *DocumentIterator {
-	tagsIt := &TagsIterator{ValueIt: valueIt, Selected: nil}
+func NewDocumentIterator(tagsIt *TagsIterator) *DocumentIterator {
 	return &DocumentIterator{tagsIt: tagsIt, current: -1}
 }
 

diff --git a/query/linkedql/steps/steps_final.go b/query/linkedql/steps/steps_final.go
@@ -15,12 +15,29 @@ func init() {
 	linkedql.Register(&Documents{})
 }
 
+func newTagsIteratorFrom(from linkedql.PathStep, selected []string, qs graph.QuadStore, ns *voc.Namespaces) (*linkedql.TagsIterator, error) {
+	fromPath, err := linkedql.BuildFrom(from, qs, ns)
+	if err != nil {
+		return nil, err
+	}
+	valueIt := linkedql.NewValueIterator(fromPath, qs)
+	return &linkedql.TagsIterator{ValueIt: valueIt, Selected: selected}, nil
+}
+
+func singleValueIteratorFrom(from linkedql.PathStep, qs graph.QuadStore, ns *voc.Namespaces) (*linkedql.ValueIterator, error) {
+	fromPath, err := linkedql.BuildFrom(from, qs, ns)
+	if err != nil {
+		return nil, err
+	}
+	return linkedql.NewValueIterator(fromPath.Limit(1), qs), nil
+}
+
 var _ linkedql.IteratorStep = (*Select)(nil)
 
 // Select corresponds to .select().
 type Select struct {
+	From linkedql.PathStep `json:"from" minCardinality:"0"`
 	Tags []string          `json:"tags"`
-	From linkedql.PathStep `json:"from"`
 }
 
 // Type implements Step.
@@ -35,19 +52,15 @@ func (s *Select) Description() string {
 
 // BuildIterator implements IteratorStep
 func (s *Select) BuildIterator(qs graph.QuadStore, ns *voc.Namespaces) (query.Iterator, error) {
-	valueIt, err := linkedql.NewValueIteratorFromPathStep(s.From, qs, ns)
-	if err != nil {
-		return nil, err
-	}
-	return &linkedql.TagsIterator{ValueIt: valueIt, Selected: s.Tags}, nil
+	return newTagsIteratorFrom(s.From, s.Tags, qs, ns)
 }
 
 var _ linkedql.IteratorStep = (*SelectFirst)(nil)
 
 // SelectFirst corresponds to .selectFirst().
 type SelectFirst struct {
+	From linkedql.PathStep `json:"from" minCardinality:"0"`
 	Tags []string          `json:"tags"`
-	From linkedql.PathStep `json:"from"`
 }
 
 // Type implements Step.
@@ -60,28 +73,20 @@ func (s *SelectFirst) Description() string {
 	return "Like Select but only returns the first result"
 }
 
-func singleValueIteratorFromPathStep(step linkedql.PathStep, qs graph.QuadStore, ns *voc.Namespaces) (*linkedql.ValueIterator, error) {
-	p, err := step.BuildPath(qs, ns)
-	if err != nil {
-		return nil, err
-	}
-	return linkedql.NewValueIterator(p.Limit(1), qs), nil
-}
-
 // BuildIterator implements IteratorStep
 func (s *SelectFirst) BuildIterator(qs graph.QuadStore, ns *voc.Namespaces) (query.Iterator, error) {
-	it, err := singleValueIteratorFromPathStep(s.From, qs, ns)
+	it, err := singleValueIteratorFrom(s.From, qs, ns)
 	if err != nil {
 		return nil, err
 	}
-	return &linkedql.TagsIterator{it, s.Tags}, nil
+	return &linkedql.TagsIterator{ValueIt: it, Selected: s.Tags}, nil
 }
 
 var _ linkedql.IteratorStep = (*Value)(nil)
 
 // Value corresponds to .value().
 type Value struct {
-	From linkedql.PathStep `json:"from"`
+	From linkedql.PathStep `json:"from" minCardinality:"0"`
 }
 
 // Type implements Step.
@@ -96,14 +101,14 @@ func (s *Value) Description() string {
 
 // BuildIterator implements IteratorStep
 func (s *Value) BuildIterator(qs graph.QuadStore, ns *voc.Namespaces) (query.Iterator, error) {
-	return singleValueIteratorFromPathStep(s.From, qs, ns)
+	return singleValueIteratorFrom(s.From, qs, ns)
 }
 
 var _ linkedql.IteratorStep = (*Documents)(nil)
 
 // Documents corresponds to .documents().
 type Documents struct {
-	From linkedql.PathStep `json:"from"`
+	From linkedql.PathStep `json:"from" minCardinality:"0"`
 }
 
 // Type implements Step.
@@ -118,13 +123,9 @@ func (s *Documents) Description() string {
 
 // BuildIterator implements IteratorStep
 func (s *Documents) BuildIterator(qs graph.QuadStore, ns *voc.Namespaces) (query.Iterator, error) {
-	p, err := s.From.BuildPath(qs, ns)
-	if err != nil {
-		return nil, err
-	}
-	it, err := linkedql.NewValueIterator(p, qs), nil
+	tagsIt, err := newTagsIteratorFrom(s.From, nil, qs, ns)
 	if err != nil {
 		return nil, err
 	}
-	return linkedql.NewDocumentIterator(it), nil
+	return linkedql.NewDocumentIterator(tagsIt), nil
 }