How to save nodes and relationships

Through this guide, you will learn how to save nodes and relationships to a graph database.

Make sure you have a running Memgraph instance. If you're not sure how to run Memgraph, check out the Memgraph Quick start.

Let's say you want to save node User and node Language, for which you have defined classes in Python:

from gqlalchemy import Memgraph, Node, Relationship, Field

db = Memgraph()

class User(Node):
    id: str = Field(index=True, exist=True, unique=True, db=db)
    username: str = Field(index=True, exist=True, unique=True, db=db)

class Language(Node):
    name: str = Field(unique=True, db=db)

info

You can also use this feature with Neo4j:

db = Neo4j(host="localhost", port="7687", username="neo4j", password="test")

Then you create and save objects with:

user = User(id="3", username="John").save(db)
language = Language(name="en").save(db)

There is another way of creating and saving objects:

user = User(id="3", username="John")
db.save_node(user)

language = Language(name="en")
db.save_node(language)

These methods will check if the node is already in Memgraph and if not, create a new one. If it existed before in Memgraph, then the internal id of that node in Memgraph remains the same.

Next, let's say that John speaks English. You need to create and save a relationship of type SPEAKS. First, we define a class which maps to the relationship in the database:

class Speaks(Relationship, type="SPEAKS"):
    pass

This relationship doesn't have any properties. To save it, you need to first create it with appropriate start and end nodes:

speaks_rel = Speaks(
    _start_node_id = user._id,
    _end_node_id = language._id
).save(db)

Another way is by first creating the relationship and then saving it using the method save_relationship():

speaks_rel = Speaks(
    _start_node_id = user._id,
    _end_node_id = language._id
)
db.save_relationship(speaks_rel)

The property _id is an internal Memgraph id - an id given to each node upon saving to the database.

Hopefully this guide has taught you how to create and save nodes and relationships. If you have any more questions, join our community and ping us on Discord.