Mutating a Graph

• Creating Vertices
• Creating Edges
• Deleting Elements
• Updating Elements
• A Note About Transactions

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Creating Vertices

Create a vertex without any properties

v = g.create_vertex()

Create a vertex with some properties

v = g.create_vertex({type: 'airport', code: 'LGA', name: 'LaGuardia Airport', city: 'New York', country_code: 'US'})

Creating Edges

Pacer edges are directed and labeled, and can optionally contain named properties.

Create an edge from vertex u to vertex v, with the label :flight.

u = g.create_vertex({type: 'airport', code: 'LGA'})
v = g.create_vertex({type: 'airport', code: 'LAX'})
u.add_edges_to(:flight, v)

Create an edge with some properties

u.add_edges_to(:flight, v, {flight_code: 'AC524', aircraft: '747'})

Notice that we can create multiple edges from u to v with the same label.

We can add edges from a vertex u to multiple vertices.

w = g.create_vertex()
u.add_edges_to(:foo, [v,w])

In the example above, the second argument was an array, but we can also pass a route of vertices.
For example, the following command creates an edge from the vertex u to any other vertex in the graph (including u itself)

u.add_edges_to(:bar, g.v())

In fact, the add_edges_to can also be applied to a route of edges.
For example, the following command creates an edge from every vertex in the graph to u.

g.v().add_edges_to(:foo, u)

As you might expect, we can also create edges from many vertices to many vertices.

g.v().add_edges_to(:foo, g.v())

Deleting Elements

Deleting a single vertex

g.v().first().delete!

Deleting a vertex will delete all edges to/from that vertex.

We can delete! all vertices in a route.

g.v().delete!

Similarly, we can delete a single edge

g.e().first().delete!

Or all edges in a route

g.e().delete!

Updating Elements

We can add a property (or update it, if it already exists) to a vertex.

g.v().first()[:foo] = 'bar'

We can also delete a property (if it exists)

g.v().first()[:foo] = nil

The same syntax works for edges.

# Add/set a property
g.e().first()[:foo] = 'bar'
# Delete a property
g.e().first()[:foo] = nil

Notice that the syntax above does not work with routes. That is, calling g.v()[:foo] = 'bar' will result in NoMethodError.

In order to update a property of every element in a route, you can use bulk_job.

g.v().bulk_job {|vertex| vertex[:foo] = 'bar'}

A Note About Transactions

Most graph databases require all changes (i.e. create, update or delete) to a graph to take place inside of a transaction.

require 'pacer-neo4j'
g = Pacer.neo4j('/path/to/graph_dir')
g.transaction do
    # Code that mutates the graph goes here ...
end

Transactions are not required by the in-memory TinkerGraph.