how to add new property to an existing relationship?

[kincheong lau]

for each existing 'product' that 'inside' a 'category', I would like to add a property in relationship 'product->category'. When I run below cypher, it create a new relationship instead of adding new property in the existing one...how can I make it 1 relationship only?

1) Existing relationship before change

(p:Product)-[r:inside]->(c.Category)

there is no property in [ r ]

2) Cypher to run

MATCH (p:Product), (c:Category)

MERGE (p)-[r:inside {type: p.id + '->' + c.id }]->(c)

3) it creates new relationship and the existing no change

(p:Product)-[r:inside {type: p.id->c.id }]->(c:Category)

(p:Product)-[r:inside]->(c:Category)

[Michael Hunger]

MATCH (p:Product)-[r:inside]->(c:Category) 

SET r.type = p.id + '->' + c.id

But I strongly recommend against setting this kind of property !!

As you can always compute the information!

MATCH (p:Product)-[r:inside]->(c:Category) 

RETURN p.id + '->' + c.id

MERGE always tries to find the WHOLE pattern and if it can't find it will CREATE it.

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[kincheong lau]

Thanks!  I was thinking adding unique property and then create index/constraint might improve performance, would that be the case?

[Michael Hunger]

No, there are no constraints on rels.

What's your use-case? Do you have an actual performance problem?

Michael

[Bikash Karmokar]

thanks a lot.