A powerful feature of using a graph database, is that you can create your own in-graph data structures — like a linked list.
This datastructure uses a single node as the list reference. The reference has an outgoing relationship to the head of the list, and an incoming relationship from the last element of the list. If the list is empty, the reference will point to it self.
Something like this:
To initialize an empty linked list, we simply create an empty node, and make it link to itself.
Query.
CREATE root-[:LINK]->root // no ‘value’ property assigned to root RETURN root
Try this query live. start n=node(*) match n-[r?]->() delete n, r; CREATE root-[:LINK]->root // no ‘value’ property assigned to root RETURN root
Adding values is done by finding the relationship where the new value should be placed in, and replacing it with a new node, and two relationships to it.
Query.
START root=node:node_auto_index(name = "ROOT")
MATCH root-[:LINK*0..]->before,// before could be same as root
after-[:LINK*0..]->root, // after could be same as root
before-[old:LINK]->after
WHERE before.value? < 25 // This is the value, which would normally
AND 25 < after.value? // be supplied through a parameter.
CREATE before-[:LINK]->({value:25})-[:LINK]->after
DELETE old
Try this query live. (1) {"name":"A","value":10} (2) {"name":"B","value":20} (3) {"name":"C","value":30} (4) {"name":"ROOT"} (1)-[:LINK]->(2) {} (2)-[:LINK]->(3) {} (3)-[:LINK]->(4) {} (4)-[:LINK]->(1) {} START root=node:node_auto_index(name = "ROOT") MATCH root-[:LINK*0..]->before,// before could be same as root after-[:LINK*0..]->root, // after could be same as root before-[old:LINK]->after WHERE before.value? < 25 // This is the value, which would normally AND 25 < after.value? // be supplied through a parameter. CREATE before-[:LINK]->({value:25})-[:LINK]->after DELETE old
Deleting a value, conversely, is done by finding the node with the value, and the two relationships going in and out from it, and replacing with a new value.
Query.
START root=node:node_auto_index(name = "ROOT") MATCH root-[:LINK*0..]->before, before-[delBefore:LINK]->del-[delAfter:LINK]->after, after-[:LINK*0..]->root WHERE del.value! = 10 CREATE before-[:LINK]->after DELETE del, delBefore, delAfter
Try this query live. (1) {"name":"A","value":10} (2) {"name":"B","value":20} (3) {"name":"C","value":30} (4) {"name":"ROOT"} (5) {"value":25} (1)-[:LINK]->(2) {} (2)-[:LINK]->(5) {} (3)-[:LINK]->(4) {} (4)-[:LINK]->(1) {} (5)-[:LINK]->(3) {} START root=node:node_auto_index(name = "ROOT") MATCH root-[:LINK*0..]->before, before-[delBefore:LINK]->del-[delAfter:LINK]->after, after-[:LINK*0..]->root WHERE del.value! = 10 CREATE before-[:LINK]->after DELETE del, delBefore, delAfter