Getting started

Connecting

Before executing any neomodel code, set the connection url:

from neomodel import config
config.DATABASE_URL = 'bolt://neo4j:neo4j@localhost:7687'  # default

This must be called early on in your app, if you are using Django the settings.py file is ideal.

If you are using your neo4j server for the first time you will need to change the default password. This can be achieved by visiting the neo4j admin panel (default: http://localhost:7474 ).

You can also change the connection url at any time by calling set_connection:

from neomodel import db
db.set_connection('bolt://neo4j:neo4j@localhost:7687')

The new connection url will be applied to the current thread or process.

In general however, it is better to avoid setting database access credentials in plain sight. Neo4J defines a number of environment variables that are used in its tools and these can be re-used for other applications too.

These are:

  • NEO4J_USERNAME
  • NEO4J_PASSWORD
  • NEO4J_BOLT_URL

By setting these with (for example):

$ export NEO4J_USERNAME=neo4j
$ export NEO4J_PASSWORD=neo4j
$ export NEO4J_BOLT_URL="bolt://$NEO4J_USERNAME:$NEO4J_PASSWORD@localhost:7687"

They can be accessed from a Python script via the environ dict of module os and be used to set the connection with something like:

import os
from neomodel import config

config.DATABASE_URL = os.environ["NEO4J_BOLT_URL"]

Defining Node Entities and Relationships

Below is a definition of two related nodes Person and Country:

from neomodel import (config, StructuredNode, StringProperty, IntegerProperty,
    UniqueIdProperty, RelationshipTo)

config.DATABASE_URL = 'bolt://neo4j:password@localhost:7687'

class Country(StructuredNode):
    code = StringProperty(unique_index=True, required=True)

class Person(StructuredNode):
    uid = UniqueIdProperty()
    name = StringProperty(unique_index=True)
    age = IntegerProperty(index=True, default=0)

    # traverse outgoing IS_FROM relations, inflate to Country objects
    country = RelationshipTo(Country, 'IS_FROM')

Nodes are defined in the same way classes are defined in Python with the only difference that data members of those classes that are intended to be stored to the database must be defined as neomodel property objects. For more detailed information on property objects please see the section on Property types.

If you have a need to attach “ad-hoc” properties to nodes that have not been specified at its definition, then consider deriving from the SemiStructuredNode class.

Relationships are defined via Relationship, RelationshipTo, RelationshipFrom objects. RelationshipTo, RelationshipFrom can also specify the direction that a relationship would be allowed to be traversed. In this particular example, Country objects would be accessible by Person objects but not the other way around.

When the relationship can be bi-directional, please avoid establishing two complementary RelationshipTo, RelationshipFrom relationships and use Relationship, on one of the class definitions instead. In all of these cases, navigability matters more to the model as defined in Python. A relationship will be established in Neo4J but in the case of Relationship it will be possible to be queried in either direction.

Neomodel automatically creates a label for each StructuredNode class in the database with the corresponding indexes and constraints.

Applying constraints and indexes

After creating a model in Python, any constraints or indexes need must be applied to Neo4j and neomodel provides a script to automate this:

$ neomodel_install_labels yourapp.py someapp.models --db bolt://neo4j:neo4j@localhost:7687

It is important to execute this after altering the schema and observe the number of classes it reports.

Remove existing constraints and indexes

Similarly, neomodel provides a script to automate the removal of all existing constraints and indexes from the database, when this is required:

$ neomodel_remove_labels --db bolt://neo4j:neo4j@localhost:7687

After executing, it will print all indexes and constraints it has removed.

Create, Update, Delete operations

Using convenience methods such as:

jim = Person(name='Jim', age=3).save() # Create
jim.age = 4
jim.save() # Update, (with validation)
jim.delete()
jim.refresh() # reload properties from the database
jim.id # neo4j internal id

Retrieving nodes

Using the .nodes class property:

# Return all nodes
all_nodes = Person.nodes.all()

# Returns Person by Person.name=='Jim' or raises neomodel.DoesNotExist if no match
jim = Person.nodes.get(name='Jim')

.nodes.all() and .nodes.get() can also accept a lazy=True parameter which will result in those functions simply returning the node IDs rather than every attribute associated with that Node.

# Will return None unless "bob" exists
someone = Person.nodes.get_or_none(name='bob')

# Will return the first Person node with the name bob. This raises neomodel.DoesNotExist if there's no match.
someone = Person.nodes.first(name='bob')

# Will return the first Person node with the name bob or None if there's no match
someone = Person.nodes.first_or_none(name='bob')

# Return set of nodes
people = Person.nodes.filter(age__gt=3)

Relationships

Working with relationships:

germany = Country(code='DE').save()
jim.country.connect(germany)

if jim.country.is_connected(germany):
    print("Jim's from Germany")

for p in germany.inhabitant.all():
    print(p.name) # Jim

len(germany.inhabitant) # 1

# Find people called 'Jim' in germany
germany.inhabitant.search(name='Jim')

# Find all the people called in germany except 'Jim'
germany.inhabitant.exclude(name='Jim')

# Remove Jim's country relationship with Germany
jim.country.disconnect(germany)

usa = Country(code='US').save()
jim.country.connect(usa)
jim.country.connect(germany)

# Remove all of Jim's country relationships
jim.country.disconnect_all()

jim.country.connect(usa)
# Replace Jim's country relationship with a new one
jim.country.replace(germany)