Cypher Linked LIst: how to unshift and replace by index

Question

I am trying to create a Linked List structure with Neo/Cypher as per the recomendation here: CYPHER store order of node relationships of the same label when I create

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Answer 1

If I'm following, your nodes may belong to multiple linked lists. A simple 'next' relation is insufficient because when lists cross--share a child node--the 'next' relations will drag in all the downstream nodes of both lists. So you're making the 'next' relations unique to each list by adding the id of the parent node. (Note using the metadata id may lead to issues down the road.)

So you might have a parent p1 whose id=1, and a unique relationship 'n_p1' to link its children, and a child 'c' whose id=21 you want to add.

For the parent with no child you could add your new child by:

MATCH (c {id:21}), (p {id:1}) WHERE NOT p-[:n_p1]->() MERGE p-[:n_p1]->c

And if the parent has one or more children, find the last one that's not the same as the one being added:

MATCH (c {id:21}), (p {id:1})-[:n_p1*1..5]->(cn) WHERE NOT cn-[:n_p1]->() AND NOT cn.id=c.id MERGE cn-[:n_p1]->c

Somebody else might have a better way, but you could UNION these together. Remember the parts of a UNION must return the same columns, so just return the new child c. The whole thing might look like this:

MATCH (c {id:21}), (p {id:1}) WHERE NOT p-[:n_p1]->() MERGE p-[:n_p1]->c return c UNION MATCH (c {id:21}), (p {id:1})-[:n_p1*1..5]->(cn) WHERE NOT cn-[:n_p1]->() AND NOT cn.id=c.id MERGE cn-[:n_p1]->c return c;