TopolearnEvery Cypher query and data model is built from these four ingredients, so this is the mental model for everything else.
Neo4j stores a property graph:
- Nodes are the entities: a person, a product, an account. A node can have zero or more labels such as
:Personor:Customerthat group nodes into roles. - Relationships connect two nodes. Each has exactly one type (
:FOLLOWS,:BOUGHT), a direction from a start node to an end node, and always has both ends; there are no dangling relationships. - Properties are key/value pairs on nodes and relationships:
name: 'Ann',since: 2021. Values are strings, numbers, booleans, temporal and spatial types, or lists of those. There are no nested maps as property values.
Compared with a relational database, relationships are stored data, not computed at query time with joins. Following a relationship costs the same whether the database holds a thousand or a billion nodes, which is why multi-hop questions ("friends of friends who bought this") stay fast.
Neo4j is schema-optional: you can add labels, properties and relationship types as you go, and add constraints later.
To try it, create a free Neo4j Aura instance in the cloud, install Neo4j Desktop, or run docker run -p 7474:7474 -p 7687:7687 neo4j. Open Neo4j Browser at http://localhost:7474 to run Cypher and see results drawn as a graph; applications connect over the Bolt protocol on port 7687.
Example
// A tiny graph, written as Cypher patterns:
//
// (:Person {name: 'Ann'})-[:FOLLOWS {since: 2021}]->(:Person {name: 'Bob'})
// (:Person {name: 'Bob'})-[:WORKS_AT]->(:Company {name: 'Acme'})
//
// nodes: (variable:Label {property: value})
// relationships: -[variable:TYPE {property: value}]->
//
// Ann --FOLLOWS--> Bob --WORKS_AT--> Acme
RETURN 'nodes, relationships, labels, types, properties' AS model;Remember
- Nodes have labels; relationships have exactly one type and a direction
- Both nodes and relationships carry properties
- Relationships are stored, so traversals do not need joins
- Use Aura Free, Desktop or Docker plus Neo4j Browser to start
Watch out for
- Storing a relationship as a foreign-key-like property (author_id) instead of a real relationship.