I have run into a unique situation (bug?). Here is my query that does what
it is supposed to:
MATCH
(:Author {name: {author} })-[:WROTE_BOOK]->(b:Book {name_min: {book}
})-[:HAS_CHAPTER]->(c:Chapter {chapter: {chapter} })-[:HAS_TEXT]->(t:Text),
(lang:Language {language: {lang} }),
(version:Version {version_min: {version} })
USING INDEX b:Book(name_min)
OPTIONAL MATCH (user:User {name: {user} })-[user_likes:LIKES]->(c)
WHERE (lang)<-[:IN_LANGUAGE]-(t)-[:IN_VERSION]->(version)
RETURN
b.name AS book,
b.name_min AS book_min,
c.chapter AS chapter,
t.text AS text,
c.id AS id,
count(user_likes) > 0 AS user_likes
Think of this as a system for adding a social layer on top of text books
where users can like various chapters, books, and/or authors.
What I am doing here is returning the text from a chapter and using an
OPTIONAL MATCH for the user to see how many :LIKE relationships they have
to this chapter so I can indicate if they already have liked it. Now this
is all great, but the running time on this is about 46ms. So I added an
index hint to the query like:
MATCH
(:Author {name: {author} })-[:WROTE_BOOK]->(b:Book {name_min: {book}
})-[:HAS_CHAPTER]->(c:Chapter {chapter: {chapter} })-[:HAS_TEXT]->(t:Text),
(lang:Language {language: {lang} }),
(version:Version {version_min: {version} })
USING INDEX b:Book(name_min)
OPTIONAL MATCH (user:User {name: {user} })-[user_likes:LIKES]->(c)
USING INDEX user:User(name)
WHERE (lang)<-[:IN_LANGUAGE]-(t)-[:IN_VERSION]->(version)
RETURN
b.name AS book,
b.name_min AS book_min,
c.chapter AS chapter,
t.text AS text,
c.id AS id,
count(user_likes) > 0 AS user_likes
Now the running time is less than 4ms! Blazing fast! But I only get the
right b.name, b.name_min, c.chapter, and t.text. The c.id is the wrong and
the user_likes is always 1+ (assuming they have liked at least one chapter
somewhere. So what is happening is that the optional match is not using the
'c' variable from the MATCH above correctly as it seems to be viewing c as
a wildcard match. What is most interesting is that if it were matching all
chapters a user like, then count(user_likes) should be 30 in my test case.
But it is still counting only 1 -- the wrong 1 though.
How does adding the USING INDEX line mess this up? Any ideas?
--
You received this message because you are subscribed to the Google Groups
"Neo4j" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
