Neo4j使用简单例子（转）

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

MATCH (user:User)
WHERE user.Id = 123
SET user = { Id: 123, Age: 25, Email: '[email protected]' }
           

graphClient.Cypher
    .Match("(user:User)")
    .Where((User user) => user.Id == 123)
    .Set("user = {tatham}")
    .WithParam("tatham", new User { Id = 123, Age = 25, Email = "[email protected]" })
    .ExecuteWithoutResults();
           

Delete a user

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

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

Delete a user and all inbound relationships

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

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

Get all labels for a specific user

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

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

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

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

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
           

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
           

原文地址：https://www.cnblogs.com/ulex/p/6066083.html