How to create relationship using FOREACH

Neo4j Graph Platform
1

I have Person and Course nodes. How I can create the relationships from one Person to many Courses using FOREACH? I tried the following as the example but it returns two new empty nodes, two new nodes with Courses and one new relationship between each pair of nodes.

Match (r: Course ), (p:Person {role:'Student', firstname:'John',lastname:’Smith'})

with ["Chemistry", "Physics"] as rid_array

foreach (i in range(0,size(rid_array)-1)|

merge out = (p)-[req:HAS_COURSE]->(r {course_name: rid_array[i]}))

return out

2

Can't create node `r` with labels or properties here. The variable is already declared in this context

3 
The variables 'r' and 'p' are not being passed on. Add these varibles in line 2 and try.
with ["Chemistry", "Physics"] as rid_array, r, p
4 
Try this:

merge (p:Person {role:'Student', firstname:'John', lastname:'Smith'})

with ["Chemistry", "Physics"] as rid_array, p
 foreach (i in range(0,size(rid_array)-1)|
 merge (r:Course {course_name: rid_array[i]})
 merge (p)-[req:HAS_COURSE]->(r)
 )
5

@ameyasoft is absolutely correct, but it can be simplified, as you can iterate over the array directly.

with ["Chemistry", "Physics"] as rid_array
merge (p:Person {role:'Student', firstname:'John', lastname:'Smith'})
foreach (i in rid_array |
    merge (r:Course {course_name: i})
    merge (p)-[req:HAS_COURSE]->(r)
)
6 
If you want to use FOREACH, try this: A slight modification of @gillienfield code.

with ["Chemistry", "Physics"] as rid_array
match (p:Person {role:'Student', firstname:'John', lastname:'Smith'})
foreach (i in rid_array |
    merge (r:Course {course_name: i})
    merge (p)-[req:HAS_COURSE]->(r)
)
7

two new nodes have been created and the relationships have been added to them. I need to create just relationship from one existing node Person (John Smith) to two existing courses.

8

That is odd, as the merge will look for an existing node before it creates a new one. Also, the merge on the relationship is referencing node variables so, it shouldn't create new ones as well. We can change the merge to a match, but match is not allowed in a foreach loop, so we will need to refactor the code.

with ["Chemistry", "Physics"] as rid_array
merge (p:Person {role:'Student', firstname:'John', lastname:'Smith'})
with rid_array, p
unwind rid_array as rid
match (r:Course {course_name: rid})
merge (p)-[req:HAS_COURSE]->(r)

Screen Shot 2023-02-06 at 10.13.49 AM.png

Screen Shot 2023-02-06 at 10.14.35 AM.png

BTW- you can have multiple labels on a node. It may be a better approach to add a label for your 'role' instead of a property.

9

@glilienfield Thanks but this query creates two new nodes 'Chemistry' and 'Physics' and then creates two relationships from Person to these new nodes. I need to create just relationships from node Person ('John Smith') to existing two nodes 'Chemistry' and 'Physics' in the loop,

10

I am confused with the migration back to the old platform. Did we resolve your issue?