cypher examples

Lars Wilhelmsen edited this page Sep 26, 2017 · 7 revisions

Some Context

Neo4jClient just gives you a nice way to execute Cypher commands against a Neo4j instance. You always need to start with a working Cypher query, then you can write it in C#.

This page just shows some examples of how to translate different Cypher queries into C#.

For more explanation about how we handle parameters, immutable query objects, custom return clauses and things like that, you should really take the time to read the main Neo4jClient Cypher documentation that we have published. This page is just examples.

Neo4j Versions

Most of the examples on this page are written with Neo4j 2.0 in mind, so they skip the START clause, and use clauses like MERGE. The focus of this page is about Cypher-to-C# syntax though, and should be equally useful in helping you translate a Neo4j 1.9 query to C#.

At the end of the day, you always need to start with a working Cypher query, then work out the equivalent C#.

Need more help?

If you have a working Cypher query, but can't translate it to C#, just post it on http://stackoverflow.com/questions/tagged/neo4jclient and we'll help you out pretty quickly.

Then, once we have the answer, we can add it to this page too so it helps other people.

User class

Most of the examples below assume you have the following class, to represent the structure of a user node:

public class User
{
    public long Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public string Email { get; set; }
}

Get all users by label

This Cypher:

MATCH (user:User)
RETURN user

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Return(user => user.As<User>())
    .Results

Get specific user

This Cypher:

MATCH (user:User)
WHERE user.Id = 1234
RETURN user

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 1234)
    .Return(user => user.As<User>())
    .Results

Get a user, and the count of their friends

This Cypher:

OPTIONAL MATCH (user:User)-[FRIENDS_WITH]-(friend:User)
WHERE user.Id = 1234
RETURN user, count(friend) AS NumberOfFriends

Is this C#:

graphClient.Cypher
    .OptionalMatch("(user:User)-[FRIENDS_WITH]-(friend:User)")
    .Where((User user) => user.Id == 1234)
    .Return((user, friend) => new {
        User = user.As<User>(),
        NumberOfFriends = friend.Count()
    })
    .Results

Get a user, and all their friends

This Cypher:

OPTIONAL MATCH (user:User)-[FRIENDS_WITH]-(friend:User)
WHERE user.Id = 1234
RETURN user, collect(friend) AS NumberOfFriends

Is this C#:

graphClient.Cypher
    .OptionalMatch("(user:User)-[FRIENDS_WITH]-(friend:User)")
    .Where((User user) => user.Id == 1234)
    .Return((user, friend) => new {
        User = user.As<User>(),
        Friends = friend.CollectAs<User>()
    })
    .Results

Create a user

This Cypher:

CREATE (user:User { Id: 456, Name: 'Jim' })

Should use parameters:

CREATE (user:User {newUser})

And is this C#:

var newUser = new User { Id = 456, Name = "Jim" };
graphClient.Cypher
    .Create("(user:User {newUser})")
    .WithParam("newUser", newUser)
    .ExecuteWithoutResults();

Note that we're using an explicitly named parameter (newUser) and the query, and the WithParam method to supply it. This keeps our encoding safe, protects against Cypher-injection attacks, and improves performance by allowing query plans to be cached.

Create a user, only if they don't already exist

This Cypher:

MERGE (user:User { Id: 456 })
ON CREATE user
SET user.Name = 'Jim'

Should use parameters:

CREATE (user:User { Id: {id} })
ON CREATE user
SET user = {newUser}

And is this C#:

var newUser = new User { Id = 456, Name = "Jim" };
graphClient.Cypher
    .Merge("(user:User { Id: {id} })")
    .OnCreate()
    .Set("user = {newUser}")
    .WithParams(new {
        id = newUser.Id,
        newUser
    })
    .ExecuteWithoutResults();

Create a user and relate them to an existing one

This Cypher:

MATCH (invitee:User)
WHERE invitee.Id = 123
CREATE (invitee)-[:INVITED]->(invited:User {newUser})

Is this C#:

var newUser = new User { Id = 456, Name = "Jim" };
graphClient.Cypher
    .Match("(invitee:User)")
    .Where((User invitee) => invitee.Id == 123)
    .Create("(invitee)-[:INVITED]->(invited:User {newUser})")
    .WithParam("newUser", newUser)
    .ExecuteWithoutResults();

Relate two existing users

This Cypher:

MATCH (user1:User), (user2:User)
WHERE user1.Id = 123, user2.Id = 456
CREATE user1-[:FRIENDS_WITH]->user2

Is this C#:

graphClient.Cypher
    .Match("(user1:User)", "(user2:User)")
    .Where((User user1) => user1.Id == 123)
    .AndWhere((User user2) => user2.Id == 456)
    .Create("user1-[:FRIENDS_WITH]->user2")
    .ExecuteWithoutResults();

Relate two existing users, only if they aren't related already

This Cypher:

MATCH (user1:User), (user2:User)
WHERE user1.Id = 123, user2.Id = 456
CREATE UNIQUE user1-[:FRIENDS_WITH]->user2

Is this C#:

graphClient.Cypher
    .Match("(user1:User)", "(user2:User)")
    .Where((User user1) => user1.Id == 123)
    .AndWhere((User user2) => user2.Id == 456)
    .CreateUnique("user1-[:FRIENDS_WITH]->user2")
    .ExecuteWithoutResults();

Update a single property on a user

This Cypher:

MATCH (user:User)
WHERE user.Id = 123
SET user.Age = 25

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 123)
    .Set("user.Age = {age}")
    .WithParam("age", 25)
    .ExecuteWithoutResults();

Note: we're using parameters again to pass in data. Never do this via string concatenation like Set("user.Age = " + age.ToString()) otherwise you will introduce encoding bugs, security risks, and significantly impact your query performance by bypassing the query plan cache in Neo4j itself.

Replace all the properties on a user

This Cypher:

MATCH (user:User)
WHERE user.Id = 123
SET user = { Id: 123, Age: 25, Email: 'tatham@oddie.com.au' }

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 123)
    .Set("user = {tatham}")
    .WithParam("tatham", new User { Id = 123, Age = 25, Email = "tatham@oddie.com.au" })
    .ExecuteWithoutResults();

Delete a user

This Cypher:

MATCH (user:User)
WHERE user.Id = 123
DELETE user

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 123)
    .Delete("user")
    .ExecuteWithoutResults();

Delete a user and all inbound relationships

This Cypher:

OPTIONAL MATCH (user:User)<-[r]-()
WHERE user.Id = 123
DELETE r, user

Is this C#:

graphClient.Cypher
    .OptionalMatch("(user:User)<-[r]-()")
    .Where((User user) => user.Id == 123)
    .Delete("r, user")
    .ExecuteWithoutResults();

Get all labels for a specific user

This Cypher:

MATCH (user:User)
WHERE user.Id = 1234
RETURN labels(user)

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 1234)
    .Return(user => user.Labels())
    .Results

Get all labels for a specific user, and still the user too

This Cypher:

MATCH (user:User)
WHERE user.Id = 1234
RETURN user, labels(user)

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 1234)
    .Return(user => new {
        User = user.As<User>(),
        Labels = user.Labels()
    })
    .Results

Get a user, count their friends then add this number to the user and return.

Note: This is an example of using Neo4j 3.0 Stored Procedures. There are other ways of adding a property to an object, this is just an example of CALL and YIELD, using apoc Neo4j Stored Procedures

This Cypher:

MATCH (user:User)
WHERE user.Id = 1234
WITH user, size((user)-[:IS_FRIENDS_WITH]->(:Friend)) as numberOfFriends
CALL apoc.map.setKey(user, 'numberOfFriends', numberOfFriends) YIELD value AS userWithFriends
RETURN userWithFriends

Is this C#:

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 1234)
    .With("user, size((user)-[:IS_FRIENDS_WITH]->(:Friend)) as numberOfFriends")
    .Call("apoc.map.setKey(user, 'numberOfFriends', numberOfFriends)").Yield("value AS userWithFriends")
    .Return(userWithFriends => new {
        User = userWithFriends.As<User>()
    })
    .Results