How to Create a Graph using existing Collections (Documents and Edges)

Question

I am using pyArango Python package to create several Collections (documents (vertices) and edges). How can I programmatically create a graph using existing vertices and edges? I know how to create a graph using ArangoDB web interface "Add Graph" but that requires a tedious task because of a large number of Collections.

Hi, have you figured it out? I am facing the same problem and yet found nothing helpful... — Yikang Luo

Yikang Luo Yikang Luo · Accepted Answer · 2020-06-28T13:19:29

After inspect the network flow from the WebGui, I found out that Add graph essentially is sending a json post request with Edge and Document connection name as string input. Thus, what is prevent us using existing edges and documents is the validation built default in pyarango

def _checkCollectionList(lst):
    for colName in lst:
        if not COL.isCollection(colName):
            raise ValueError("'%s' is not a defined Collection" % colName)

graphClass = GR.getGraphClass(name)

ed = []
for e in graphClass._edgeDefinitions:
    if not COL.isEdgeCollection(e.edgesCollection):
        raise ValueError("'%s' is not a defined Edge Collection" % e.edgesCollection)
    _checkCollectionList(e.fromCollections)
    _checkCollectionList(e.toCollections)

    ed.append(e.toJson())

_checkCollectionList(graphClass._orphanedCollections)

To overcome this issue, we only need to implement class first before create graph. for e.g., I have two documents collections people and department, and I want to create a graph which:

people -> knowns -> people
people -> belongs_to -> department

suppose I already have collection "people", "department", "knowns", "belongs_to" in my arangodb, the code to create a graph is as following:

from pyArango.collection import Collection, Field
from pyArango.graph import Graph, EdgeDefinition

class knowns(Edges):
    pass

class belongs_to(Edges):
    pass

class people(Collection):
    pass

class department(Collection):
    pass

# Here's how you define a graph
class MyGraph(Graph) :
    _edgeDefinitions = [EdgeDefinition('knowns', ['people'], ['people']),
                        EdgeDefinition('belongs_to', ['people'], ['department'])]
    _orphanedCollections = []

theGraph = arrango_db.createGraph(name="MyGraph", createCollections=False)

Be aware that the class name is exactly the same as the string I passed into graph creation. Now we have the graph created in ArangoDB:

How to Create a Graph using existing Collections (Documents and Edges)

2 Answers