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cypher examples

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dandeto edited this page Oct 14, 2024 · 9 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.

Need more help?

You always need to start with a working Cypher query, then work out the equivalent C#.

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#:

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

Get specific user

This Cypher:

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

Is this C#:

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

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#:

await 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()
    })
    .ResultsAsync

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#:

await 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>()
    })
    .ResultsAsync

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" };
await graphClient.Cypher
    .Create("(user:User {newUser})")
    .WithParam("newUser", newUser)
    .ExecuteWithoutResultsAsync();

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" };
await graphClient.Cypher
    .Merge("(user:User { Id: {id} })")
    .OnCreate()
    .Set("user = {newUser}")
    .WithParams(new {
        id = newUser.Id,
        newUser
    })
    .ExecuteWithoutResultsAsync();

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" };
await graphClient.Cypher
    .Match("(invitee:User)")
    .Where((User invitee) => invitee.Id == 123)
    .Create("(invitee)-[:INVITED]->(invited:User {newUser})")
    .WithParam("newUser", newUser)
    .ExecuteWithoutResultsAsync();

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#:

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

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#:

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

Update a single property on a user

This Cypher:

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

Is this C#:

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

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: 'user@domain.com' }

Is this C#:

await graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 123)
    .Set("user = {person}")
    .WithParam("person", new User { Id = 123, Age = 25, Email = "user@domain.com" })
    .ExecuteWithoutResultsAsync();

Delete a user

This Cypher:

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

Is this C#:

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

Delete a user and all inbound relationships

This Cypher:

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

Is this C#:

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

Get all labels for a specific user

This Cypher:

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

Is this C#:

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

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#:

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

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

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

await 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>()
    })
    .ResultsAsync

Get the entire path from a user to it's relationships of distance n=1 and return as JSON.

This Cypher:

MATCH path = (user:User)-[r]->(n)
RETURN path

Is this C#:

var json = await graphClient.Cypher
    .Match("path = (user:User)-[r]->(n)")
    .Return<string>("path").ResultsAsync;

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  • Licensed under MS-PL. See LICENSE in the root of this repository for full license text.

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