Add edgeCollections and vertexCollections traversal options.

3.7/aql/graphs-traversals.md

@@ -94,6 +94,22 @@ FOR vertex[, edge[, path]]
       duplicate edge
     - "none" – no uniqueness check is applied on edges. **Note:**
       Using this configuration the traversal will follow edges in cycles.
+  - **edgeCollections** (string\|array): Optionally restrict edge
+    collections the traversal may visit. If omitted, or an
+    empty array is specified, then there are no restrictions.
+    - A string parameter is treated as the equivalent of an array with a single
+      element.
+    - Each element of the array should be a string containing the name of an
+      edge collection.
+  - **vertexCollections** (string\|array): Optionally restrict vertex
+    collections the traversal may visit. If omitted, or an empty array is
+    specified, then there are no restrictions.
+    - A string parameter is treated as the equivalent of an array with a single
+      element.
+    - Each element of the array should be a string containing the name of a
+      vertex collection.
+    - The starting vertex is always allowed, even if it does not belong to one
+      of the collections specified by a restriction.
 
 ### Working with collection sets
 
@@ -109,7 +125,8 @@ FOR vertex[, edge[, path]]
 
 Instead of `GRAPH graphName` you may specify a list of edge collections. Vertex
 collections are determined by the edges in the edge collections. The traversal
-options are the same as with the [named graph variant](#working-with-named-graphs).
+options are the same as with the [named graph variant](#working-with-named-graphs),
+though the `edgeCollections` restriction option is redundant in this case.
 
 If the same edge collection is specified multiple times, it will behave as if it
 were specified only once. Specifying the same edge collection is only allowed when

3.7/release-notes-new-features37.md

@@ -168,6 +168,33 @@ the graph, which can be expensive. In case it is known that only certain edges
 from the named graph are needed, the `edgeCollections` option can be a handy
 performance optimization.
 
+### Traversal collection restrictions
+
+Added traversal options `vertexCollections` and `edgeCollections` to restrict
+traversal to certain vertex or edge collections.
+
+The use case for `vertexCollections` is to not follow any edges that will point
+to other than the specified vertex collections, e.g.
+
+    FOR v, e, p IN 1..3 OUTBOUND 'products/123' components 
+      OPTIONS { vertexCollections: [ "bolts", "screws" ] }
+
+The traversal's start vertex is always considered valid, regardless of whether
+it is present in the `vertexCollections` option.
+
+The use case for `edgeCollections` is to not take into consideration any edges
+from edge collections other than the specified ones, e.g.
+
+    FOR v, e, p IN 1..3 OUTBOUND 'products/123' GRAPH 'components' 
+      OPTIONS { edgeCollections: [ "productsToBolts", "productsToScrews" ] }
+
+This is mostly useful in the context of named graphs, when the named graph
+contains many edge collections. Not restricting the edge collections for the
+traversal will make the traversal search for edges in all edge collections of
+the graph, which can be expensive. In case it is known that only certain edges
+from the named graph are needed, the `edgeCollections` option can be a handy
+performance optimization.
+
 ### AQL functions added
 
 The following AQL functions have been added in ArangoDB 3.7: