Working with the FOREACH clause

The FOREACH clause can be used to process a list and update the data in a graph. It can only be used to update data using the CREATE, MERGE, SET, DELETE, REMOVE, and FOREACH clauses. It is not possible to use the MATCH clause within FOREACH. Also, the variables in the context of the FOREACH clause are limited to its scope only and there is no option to remove those variables to be used after FOREACH.

Let’s look at an example usage:

MATCH (p:Patient)
WHERE p.marital IS NULL
WITH collect(p) as nodes
FOREACH( n in nodes | SET n:UNKNOWN_STATUS)

In this query, we are finding all the patients whose marital status is null, collecting all those patients into a list, and then using the FOREACH clause to add an UNKNOWN_STATUS label.

We can see from the screenshot that we have updated 388 patient nodes with the new label.

Figure 8.15 – Using FOREACH to add a new label to the node

Another usage of the FOREACH clause...