Neo4j使用简单例子
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
