How to remove relations while iteration with UNWIND using cypher

Question

The following query getting all groups of specific user then unwind on each result(each group) and should remove all incoming relations only if count relations to that group is 1.

example: group1<-user1  (will delete the incoming relationship to the group)

         group1-<user1 
         group1-<user2 (will remain all incoming relationships to the group)

can assist complete it?

MATCH (me:userId{{1})-[rel:relation_group]-(allGroups:GROUP)
unwind userGroups as group  
 //how to use CASE or WHERE in order to check if this group 
has only 1 relationship just remove it

Thanks.

Christophe Willemsen · Accepted Answer · 2016-06-08T08:44:00.067

3

You can use size in WHERE, example :

MATCH (me:userId{{1})-[rel:relation_group]-(allGroups:GROUP)
WHERE size((allGroups)<-[:relation_group]-()) = 1
DELETE rel

You don't need to iterate, by default the subsequent clauses after a MATCH will be executed for each row found in the MATCH, so let's say the first MATCH returns the following :

me     rel     allGroups
1      rel3     node5
1      rel4     node6

Then the DELETE will be executed for the first row, then for the second row, etc...

edited Jun 08 '16 at 08:44

answered Jun 08 '16 at 06:41

Christophe Willemsen

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but how do u iterate this way on each group? as u'll get list of groups and need to check for each one if the number of incoming relationships is 1 remove it else remain it – rayman Jun 08 '16 at 06:43
You don't need to iterate, just add the direction to the pattern in the WHERE clause – Christophe Willemsen Jun 08 '16 at 06:45
How the size actually iterate on each group from allGroups? – rayman Jun 08 '16 at 08:41
I added a little explanation – Christophe Willemsen Jun 08 '16 at 08:44
Thanks. so why we have UNWIND or FOREACH if we can iterate on results row by row as default behavior ? – rayman Jun 08 '16 at 08:52
I suggest you take some available cypher online courses / tutorials / graphgists to learn more about cypher ;-) – Christophe Willemsen Jun 08 '16 at 08:53
you right. doing my best to cover it all. just every-time I find out new concepts – rayman Jun 08 '16 at 08:56
1

Thats cool to discover new stuff, otherwise we would be bored :) – Christophe Willemsen Jun 08 '16 at 08:56

How to remove relations while iteration with UNWIND using cypher

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