Neo4j / Cypher查询语法反馈

Question

I'm developing a kind of reddit service to learn Neo4j. Everything works fine, I just want to get some feedback on the Cypher query to get the most recent news stories, the author and number of comments, likes and dislikes.

I'm using Neo4j 2.0.

MATCH comments = (n:news)-[:COMMENT]-(o)
MATCH likes = (n:news)-[:LIKES]-(p)
MATCH dislikes = (n:news)-[:DISLIKES]-(q)
MATCH (n:news)-[:POSTED_BY]-(r)
WITH n, r, count(comments) AS num_comments, count(likes) AS num_likes, count(dislikes) AS num_dislikes
ORDER BY n.post_date
LIMIT 20
RETURN *

o , p , q , r are all nodes with the label user . Should the label be added to the query to speed it up?

Is there anything else you see that I could optimize?

Answer 1

I think you're going to want to get rid of the multiple matches. Cypher will filter on each one, filtering through one another, rather than getting all the information.

I would also avoid the paths like comments, and rather do the count on the nodes you are saving. When you do MATCH xyz = (a)-[:COMMENT]-(b) then xyz is a path, which contains the source, relationship and destination node.

MATCH (news:news)-[:COMMENT]-(comment),(news:news)-[:LIKES]-(like),(news:news)-[:DISLIKES]-(dislike),(news:news)-[:POSTED_BY]-(posted_by) 
WHERE news.post_date > 0 
WITH news, posted_by, count(comment) AS num_comments, count(like) AS num_likes, count(dislike) AS num_dislikes 
ORDER BY news.post_date 
LIMIT 20 
RETURN *

Answer 2

I would do something like this.

MATCH (n:news)-[:POSTED_BY]->(r)
WHERE n.post_date > {recent_start_time}
RETURN n, r, 
        length((n)<-[:COMMENT]-()) AS num_comments,
        length((n)<-[:LIKES]-()) AS num_likes,
        length((n)<-[:DISLIKES]-()) AS num_dislikes,
ORDER BY n.post_date DESC
LIMIT 20

To speed it up and have not neo search over all your posts, I would probably index the post-date field (assuming it doesn't contain time information). And then send this query in for today, yesterday etc. until you have your 20 posts.

MATCH (n:news {post_date: {day}})-[:POSTED_BY]->(r)
RETURN n, r, 
        length((n)<-[:COMMENT]-()) AS num_comments,
        length((n)<-[:LIKES]-()) AS num_likes,
        length((n)<-[:DISLIKES]-()) AS num_dislikes,
ORDER BY n.post_date DESC
LIMIT 20