TW Neo4j

MERGE is a powerful and misunderstood component of the CYPHER toolbox. Assume you have two :Person nodes each with a name property ('Adam' and 'Bob'). You might assume that you could MERGE as follows to create a [:KNOWS] relationship: MERGE (a:Person {name:'Adam'})-[r:KNOWS]->(b:Person {name:'Bob'}); and you'd be correct, it works perfectly Always remember MERGE is based on matching the entire pattern in the statement. Say you now want to set the age of Adam to 21 in the same statement. You might think it's as simple as MERGE (a:Person {name:'Adam',age:21})-[r:KNOWS]->(b:Person {name:'Bob'}); will create 2 new Person nodes and a [:KNOWS] relationship. If there is a unique constraint on :Person (name) there will be errors thrown and no new nodes or relationships. Why, the initial part of the MERGE 'looks' for a pattern match on the :Person node of name:'Adam' and age:21, it doesn't create a property. No m...

From Neo4j v3.5 and onwards you can use a generic CYPHER statement: match (s)-[r]->(e) with s,e,type(r) as typ, tail(collect(r)) as coll foreach(x in coll | delete x) to remove all duplicate relationships in your Neo4j Graph Database. You can refine the control over what is deleted by adding in a node label or relationship type. We're collecting the relationships and grouping by type (as well as start and end node), so if any collection is greater than 1, then there are multiple relationships with the same type. TAIL removes the first element from the collect statement, but the first relationship back into rows then delete them. If you don't have labels to use for your query, then the query will be graph-wide, which is likely to take much longer to execute, and may encounter issues if the set of relationships to delete is too large to handle all at once.

 How many Nodes and relationships are in your Graph? You could look on the left hand side of the Neo4j Browser, but that would be cheating. For nodes: MATCH (n) RETURN count(n) For Relationships: MATCH ()-[r]->() RETURN count(r) The above CYPHER statements assume all nodes and relationships are to be counted. Once you start adding in labels and relationships you will filter the return values For Outgoing Relationships: MATCH (a)-[r]->() RETURN count(a) This counts nodes with outgoing relationships only.

In a Graph Database Relationships between the nodes are considered to be as important, if not more important than the nodes themselves. A Relationship joins two nodes or 'loops-back' to the same node. The relationship can be created or deleted but cannot be renamed. How to delete relationship MATCH (n { name: 'Greg' })-[r:KNOWS]->() DELETE r To rename a Relationship you do a simultaneous create and delete. Create a new relationship and delete the old as below: Rename relationship MATCH (n)-[rel:IS_CONNECTED_TO]->(m) MERGE (n)-[:KNOWS]->(m) DELETE rel MATCH (n)-[rel:IS_CONNECTED_TO]->(m) WITH rel CALL apoc.refactor.setType(rel, 'KNOWS') YIELD input, output RETURN *