Cypher Query String Problem

Neo4j Graph Platform Cypher
1

I have a simple Bill of Materials DB

CREATE (p1:Part{name:"Root"})
CREATE (p2:Part{name:"Sub Assy 1"})
CREATE (p3:Part{name:"Sub Assy 2"})
CREATE (p4:Part{name:"Sub Assy 3"})
CREATE (p5:Part{name:"Part 1"})
CREATE (p6:Part{name:"Part 2"})
CREATE (p1)<-[:CHILD_OF{Index:1}]-(p2)
CREATE (p1)<-[:CHILD_OF{Index:2}]-(p3)
CREATE (p1)<-[:CHILD_OF{Index:3}]-(p4)
CREATE (p2)<-[:CHILD_OF{Index:1}]-(p5)
CREATE (p2)<-[:CHILD_OF{Index:2}]-(p6)
CREATE (p3)<-[:CHILD_OF{Index:1}]-(p2)

This query gives the expected output in the neo4j browser

MATCH p = (root:Part { name:"Root" })<-[:CHILD_OF *0..]-(c:Part) with *, relationships(p) as i
RETURN REDUCE (path = '1', index IN i | path + '.' + index.Index) AS path, c.name as name
ORDER BY path

Result:
╒═════════╤════════════╕
│"path" │"name" │
╞═════════╪════════════╡
│"1" │"Root" │
├─────────┼────────────┤
│"1.1" │"Sub Assy 1" │
├─────────┼────────────┤
│"1.1.1" │"Part 1" │
├─────────┼────────────┤
│"1.1.2" │"Part 2" │
├─────────┼────────────┤
│"1.2" │"Sub Assy 2" │
├─────────┼────────────┤
│"1.2.1" │"Sub Assy 1" │
├─────────┼────────────┤
│"1.2.1.1" │"Part 1" │
├─────────┼────────────┤
│"1.2.1.2" │"Part 2" │
├─────────┼────────────┤
│"1.3" │"Sub Assy 3" │
└─────────┴────────────┘

Using the grand stack api:
I defined the following types and query in my schema

type Part {
name: String
}

type Tree {
path: String
name: String
}

type Query {
tree(root: String):[Part]
@cypher(statement:
"""MATCH p = (this)<-[:CHILD_OF *0..]-(c:Part) with *, relationships(p) as i
RETURN REDUCE (path = '1', index IN i | path + ',' + index.Index) AS path, c.name as name
ORDER BY path"""
)
}

GraphQL Playground:

query{tree(root: "Root"){name}}

Returns:
Errors": [
{
"message": "String("1") (of class org.neo4j.values.storable.StringWrappingStringValue)",

so it doesn't seem to like the '1' string supplied for path = '1'

Desperately trying to get something to work I try:

type Query {
tree(root: String):[Part]
@cypher(statement:
"""MATCH p = (this)<-[:CHILD_OF *0..]-(c:Part) with *, relationships(p) as i
RETURN c"""
)
}

Which at least returns something:
{
"data": {
"tree": [
{
"name": "Root"
},
{
"name": "Sub Assy 1"
},
{
"name": "Sub Assy 1"
},
{
"name": "Sub Assy 1"
},
{
"name": "Sub Assy 1"
},
.....

So I can only conclude that there is something wrong with '1' in this line of my @cypher statement

RETURN REDUCE (path = '1', index IN i | path + ',' + index.Index) AS path, c.name as name

HELP PLEASE!

2

Your initial value of path inside reduce() is '1', a string, but your expression is attempting to concatenate that with integers provided by index.Index. Have you tried wrapping that part in toString() to ensure you're concatenating two strings?

3

Thanks for the suggestion Terry.

I changed my query to:
"""MATCH p = (this)<-[:CHILD_OF *0..]-(c:Part) with *, relationships(p) as i
RETURN REDUCE (path = '1', index IN i | path + ',' + toString(index.Index)) AS path, c.name as name
ORDER BY path"""

I'm still getting the same complaint in the playground:
"message": "String("1") (of class org.neo4j.values.storable.StringWrappingStringValue)",

Is it strange that the same query will run fine in neo4j and not graphql playground?

4

I think the problem might be your GraphQL schema indicates that querying tree will return a list of Part objects ([Part]) -

but your cypher is returning a simple string.

You could try changing your schema to expect a string in return:

tree(root: String): String

or adjust your return statement to return data that matches the Part schema:

RETURN { name: REDUCE (path = '1',...) }

5

My neo4j query correctly returns Tree fields so I tried:
type Query {
tree(root: String):[Tree]
@cypher(statement:
"""MATCH p = (this)<-[:CHILD_OF *0..]-(c:Part) with *, relationships(p) as i
RETURN REDUCE (path = '1', index IN i | path + '.' + index.Index) AS path, c.name as name
ORDER BY path"""
)
}

I'm still getting the error
"message": "String("1") (of class org.neo4j.values.storable.StringWrappingStringValue)"

so what exactly is "class org.neo4j.values.storable.StringWrappingStringValue" ?

tree(root: String): String didn't work.