Graph Collections (#52)

* Highlighting boolean values

* Adding vertex and edge collection skeleton

* Refactoring serializers

* Using randomized graph name

* Improving helper types

* Facilitating edge and vertex collection creation

* Vertex collection management

* Edge collection management

* Adding cluster testcase

* Adding note about dictionary-like indexing

* Inserting and retrieving vertex documents

* Moving methods from StandardCollection to base Collection so they are available to other subclasses

* Adding CRUD for vertex collections

* Adding "has" for vertex collections

* Marking tests as asyncio

* Inserting and retrieving edges

* Event loop scope

* Event loop scope again

* Updating edge

* Edges CRUD

* Extra edge methods

* Fixing lint

* Added github gist example

* Adding graph docs

* Adding graphs example in the readme

Author: apetenchea

README.md

@@ -73,7 +73,67 @@ async def main():
             student_names = []
             async for doc in cursor:
                 student_names.append(doc["name"])
+```
+
+Another example with [graphs](https://docs.arangodb.com/stable/graphs/):
 
+```python
+async def main():
+    from arangoasync import ArangoClient
+    from arangoasync.auth import Auth
+
+    # Initialize the client for ArangoDB.
+    async with ArangoClient(hosts="http://localhost:8529") as client:
+        auth = Auth(username="root", password="passwd")
+
+        # Connect to "test" database as root user.
+        db = await client.db("test", auth=auth)
+
+        # Get the API wrapper for graph "school".
+        if await db.has_graph("school"):
+            graph = db.graph("school")
+        else:
+            graph = await db.create_graph("school")
+
+        # Create vertex collections for the graph.
+        students = await graph.create_vertex_collection("students")
+        lectures = await graph.create_vertex_collection("lectures")
+
+        # Create an edge definition (relation) for the graph.
+        edges = await graph.create_edge_definition(
+            edge_collection="register",
+            from_vertex_collections=["students"],
+            to_vertex_collections=["lectures"]
+        )
+
+        # Insert vertex documents into "students" (from) vertex collection.
+        await students.insert({"_key": "01", "full_name": "Anna Smith"})
+        await students.insert({"_key": "02", "full_name": "Jake Clark"})
+        await students.insert({"_key": "03", "full_name": "Lisa Jones"})
+
+        # Insert vertex documents into "lectures" (to) vertex collection.
+        await lectures.insert({"_key": "MAT101", "title": "Calculus"})
+        await lectures.insert({"_key": "STA101", "title": "Statistics"})
+        await lectures.insert({"_key": "CSC101", "title": "Algorithms"})
+
+        # Insert edge documents into "register" edge collection.
+        await edges.insert({"_from": "students/01", "_to": "lectures/MAT101"})
+        await edges.insert({"_from": "students/01", "_to": "lectures/STA101"})
+        await edges.insert({"_from": "students/01", "_to": "lectures/CSC101"})
+        await edges.insert({"_from": "students/02", "_to": "lectures/MAT101"})
+        await edges.insert({"_from": "students/02", "_to": "lectures/STA101"})
+        await edges.insert({"_from": "students/03", "_to": "lectures/CSC101"})
+
+        # Traverse the graph in outbound direction, breath-first.
+        query = """
+            FOR v, e, p IN 1..3 OUTBOUND 'students/01' GRAPH 'school'
+            OPTIONS { bfs: true, uniqueVertices: 'global' }
+            RETURN {vertex: v, edge: e, path: p}
+            """
+
+        async with await db.aql.execute(query) as cursor:
+            async for doc in cursor:
+                print(doc)
 ```
 
 Please see the [documentation](https://python-arango-async.readthedocs.io/en/latest/) for more details.