Neo4j Cypher查询:订单集合，取前n个元素 [英] Neo4j Cypher query: order collection, take first n elements

问题描述

我无法为此社交网络类型的应用程序编写Cypher查询.它涉及到用户添加帖子(基本上是带有说明的图片)，用户可以查看这些帖子.

I'm having trouble writing a Cypher query for this social networking type of application. It involves users that add posts (essentially an image with a description), which users can review.

在Cypher中，图形模型是这样的: (user)-[:WROTE_REVIEW]->(review)-[:EVALUATES]->(post)

In Cypher the graph model is this: (user)-[:WROTE_REVIEW]->(review)-[:EVALUATES]->(post)

我要编写的查询应返回特定用户已审阅的所有帖子，以及有关帖子评论的一些常规信息.

The query I'm trying to write should return all the posts that a particular user has reviewed, along with some general information about the reviews of a post.

这包括:

1. (帖子的ID)
2. 帖子的图片
3. 帖子的描述
4. 此帖子的评论总数
5. 此帖子的审阅者总数
6. 此帖子的最后6位评论者的头像，按评论日期排序，降序

1. (the post's ID)
2. the post's image
3. the post's description
4. the total number of reviews of this post
5. the total number of reviewers of this post
6. the avatars of the last 6 reviewers of this post, ordered by the date of the review, descending

我认为我已经完成了前五个项目，但是第6个项目给我带来了麻烦.下面的查询为我提供了所有的化身，而我只需要最后的6个.

I think I've managed to complete the first five items, but item 6 is giving me trouble. The query below gives me all of the avatars, while I only need the last 6.

START user=node(2515)
MATCH (user)-[:WROTE_REVIEW]->()-[:EVALUATES]->(post)
WITH distinct post
MATCH (review)-[:EVALUATES]->(post)
WITH post, count(review) as reviews
MATCH (reviewer)-[:WROTE_REVIEW]->()-[:EVALUATES]->(post)
WITH post, reviews, count(distinct reviewer) as reviewers, collect(distinct reviewer.Avatar) as avatars
ORDER BY post.CreationTime DESC
RETURN post.Id, post.Image, post.Description, reviews, reviewers, avatars;

有人可以告诉我如何按评论日期(即review.CreationTime)降序排列化身，并获取前六个项目吗?

Can someone show me how to order the avatars by review date (i.e. review.CreationTime) descending, and take the first six items?

谢谢！

推荐答案

Neo4j 2.0中的集合片是关键.由于出现了一些重复项，因此我必须在结果中放入一些distinct子句.这就是我最终得到的:

The collection slices in Neo4j 2.0 were the key. I had to put in some distinct clauses in my results since some duplicates were coming up. This is what I ended up with:

START user=node(2515)
MATCH (user)-[:WROTE_REVIEW]->()-[:EVALUATES]->(post)
WITH distinct post
MATCH (review)-[:EVALUATES]->(post)
WITH post, count(review) as reviews
MATCH (reviewer)-[:WROTE_REVIEW]->(review)-[:EVALUATES]->(post)
WITH distinct post, reviewer, review, reviews
ORDER BY review.CreationTime, post.CreationTime DESC
RETURN post.Id AS postId, post.Image AS postImage, post.Description AS postDescription, reviews AS Reviews, count(distinct reviewer) AS Reviewers, collect(distinct reviewer.Avatar)[0..5] AS Avatars

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