engine: graph: Pass through the graph struct

We want to use it in the resources.

engine/graph/engine.go

@@ -191,7 +191,7 @@ func (obj *Engine) Commit() error {
 
 		obj.waits[vertex] = &sync.WaitGroup{}
 		obj.state[vertex] = &State{
-			//Graph: obj.graph, // TODO: what happens if we swap the graph?
+			Graph:  obj.graph, // Update if we swap the graph!
 			Vertex: vertex,
 
 			Program:  obj.Program,
@@ -329,14 +329,14 @@ func (obj *Engine) Commit() error {
 	// the changes that we'd made to the previously primary graph. This is
 	// because this function is meant to atomically swap the graphs safely.
 
-	// TODO: update all the `State` structs with the new Graph pointer
-	//for _, vertex := range obj.graph.Vertices() {
-	//	state, exists := obj.state[vertex]
-	//	if !exists {
-	//		continue
-	//	}
-	//	state.Graph = obj.graph // update pointer to graph
-	//}
+	// Update all the `State` structs with the new Graph pointer.
+	for _, vertex := range obj.graph.Vertices() {
+		state, exists := obj.state[vertex]
+		if !exists {
+			continue
+		}
+		state.Graph = obj.graph // update pointer to graph
+	}
 
 	return nil
 }

engine/graph/state.go

@@ -32,7 +32,7 @@ import (
 // State stores some state about the resource it is mapped to.
 type State struct {
 	// Graph is a pointer to the graph that this vertex is part of.
-	//Graph pgraph.Graph
+	Graph *pgraph.Graph
 
 	// Vertex is the pointer in the graph that this state corresponds to. It
 	// can be converted to a `Res` if necessary.
@@ -190,6 +190,16 @@ func (obj *State) Init() error {
 			return res.Recv()
 		},
 
+		// FIXME: pass in a safe, limited query func instead?
+		// TODO: not implemented, use FilteredGraph
+		//Graph: func() *pgraph.Graph {
+		//	_, ok := obj.Vertex.(engine.CanGraphQueryRes)
+		//	if !ok {
+		//		panic("res does not support the GraphQuery trait")
+		//	}
+		//	return obj.Graph // we return in a func so it's fresh!
+		//},
+
 		World:  obj.World,
 		VarDir: obj.varDir,
 

engine/resources.go

@@ -120,6 +120,12 @@ type Init struct {
 
 	// Other functionality:
 
+	// Graph is a function that returns the current graph. The returned
+	// value won't be valid after a graphsync so make sure to call this when
+	// you are about to use it, and discard it right after.
+	// FIXME: it might be better to offer a safer, more limited, GraphQuery?
+	//Graph func() *pgraph.Graph // TODO: not implemented, use FilteredGraph
+
 	// World provides a connection to the outside world. This is most often
 	// used for communicating with the distributed database.
 	World World