Neo4j support for deferred constraints

Question

Suppose that for certain nodes, attributes have unique constraints defined on them.

When cloning nodes, we copy properties from original to cloned node and then modify the unique attributes on the cloned node.

However, neo4j exhibits eager constraint evaluation and seems to fail as soon as unique properties are replicated from original to cloned node.

Is there are way to differ the constraint evaluation to the end of the transaction?

Or some workaround that can mitigate the problem for the timebeing.

Sample cypher for illustrating the problem:

Create unique constraint for nodes labelled y on attribute id.
```
create constraint on (y:y) assert y.id is unique;
```

Create a few y nodes.

create (y:y{id: 1}) return y;
create (y:y{id: 2}) return y;

Now, try to clone the y node with the largest id, and assign new ids.

match (y:y) 
with max(y.id) as maxid
match (lasty:y{id: maxid})
unwind range(1, 10) as i
create (nexty:y)
set nexty = lasty
set nexty.id = maxid + i
return nexty;

The above cypher fails fast with the below error:

Node 5368657 already exists with label y and property "id"=[2]

Jim Biard Jim Biard · Accepted Answer · 2014-09-05T13:07:16

Mehul,

Change your query to this:

MATCH(y:y)
WITH max(y.id) AS maxid
MATCH (lasty:y { id : maxid})
UNWIND range(1, 10) AS i
CREATE (nexty)
SET nexty = lasty
SET nexty.id = lasty.id + 1
SET nexty :y
RETURN nexty

This creates the new node without a label, transfers and updates the properties, then adds the label.

Grace and peace,

Jim

Neo4j support for deferred constraints

1 Answers