Working with the UNWIND clause
We saw the usage of FOREACH in the previous section and explored how we can iterate a list and update the graph. But, its usage is limited. If we want to retrieve data from a graph based on the data in a list before we can update the graph, then it is not possible with FOREACH. The UNWIND clause allows us to be able to do this. Also, if we want to return some data while processing a list, then UNWIND is the option to do this.
Let’s take a look at the query we built to add a label in the previous section and build it using UNWIND:
MATCH (p:Patient) WHERE p.marital IS NULL WITH collect(p) as nodes UNWIND nodes as n SET n:UNKNOWN_STATUS
This does exactly what the FOREACH query did earlier. We find the patients who do not have a marital property set, and then we collect those nodes into a list and unwind that list to process one node at a time.
We can see from the screenshot that we updated 388 nodes, which is exactly what happened when...