CODEWITHSUNDEEP
neo4jcypher
Lx2pwn
Lx2pwn

Reputation: 323

problem with a query which has OPTIONAL MATCH in neo4j

Consider the following schema, where orange nodes are of type Friend and pink node is of type fbUser.

enter image description here

The query that I am trying to write goes as follows:

I'm trying to match all nodes which have a specific name in a specific range of time and optionally related to each Friend node, every tagged_together relationship

So I wrote the following query:

MATCH x=(:fbUser {graph_information:['admin', 'facebook']})--(f:Friend) 
OPTIONAL MATCH y=(f)-[s:TAGGED_TOGETHER]-(d:Friend) 
WITH x,f,y,d,s 
WHERE  
    f.name=~ '(?i).*ruggeri.*' AND  
    f.timestamp>'2016-02-22' AND f.timestamp<'2020-02-22' AND
    d.timestamp>'2016-02-22' AND d.timestamp<'2020-02-22'
RETURN x,y

In this specific case,the output is correctly what I want, in fact I have this:

enter image description here

but if run the query with this line

WHERE  
        f.name=~ '(?i).*kirby.*' AND  
        f.timestamp>'2016-02-22' AND f.timestamp<'2020-02-22' AND
        d.timestamp>'2016-02-22' AND d.timestamp<'2020-02-22'

I expect this output

enter image description here

but I receive (no changes, no records)

Why?

What I've understand so far is that if an optional match doesn't have any results it returns null.

Upvotes: 0

Views: 66

Answers (1)

TheTeacher
TheTeacher

Reputation: 510

Here , 

WHERE  
        f.name=~ '(?i).*kirby.*' AND  
        f.timestamp>'2016-02-22' AND f.timestamp<'2020-02-22' AND
        d.timestamp>'2016-02-22' AND d.timestamp<'2020-02-22'

When there are no tagged friends ,’d’ will be null and it cannot pass through these d.timestamp conditions

You can update your query like following to get the expected results ,

MATCH x=(:fbUser {graph_information:['admin', 'facebook']})--(f:Friend) 
OPTIONAL MATCH y=(f)-[s:TAGGED_TOGETHER]-(d:Friend) 
WITH x,f,y,d,s, case d when null then [] else [1] end as iterList 
WHERE  
    f.name=~ '(?i).*ruggeri.*' AND  
    f.timestamp>'2016-02-22' AND f.timestamp<'2020-02-22' AND ALL (x in iterList WHERE 
    d.timestamp>'2016-02-22' AND d.timestamp<'2020-02-22') 
RETURN x,y

I am creating an iteration list based on the d value . So , when it’s null , we won’t check the time stamps on d, since we are iterating through empty list . When d is not null, we will the time stamps on d .

Upvotes: 2

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