RELATE
is in the middle of MATCH
and CREATE
- it will match what it can, and create what is missing. RELATE
will always make the least change possible to the graph - if it can use parts of the existing graph, it will.
Another difference to MATCH
is that RELATE
assumes the pattern to be unique. If multiple matching subgraphs are
found an exception will be thrown.
RELATE
is used to describe the pattern that should be found or created.
Query
START left=node(1), right=node(3,4) RELATE left-[r:KNOWS]->right RETURN r
The left node is matched agains the two right nodes. One relationship already exists and can be matched, and the other relationship is created before it is returned.
If the pattern described needs a node, and it can’t be matched, a new node will be created.
Query
START root=node(2) RELATE root-[:LOVES]-someone RETURN someone
The root node doesn’t have any LOVES relationships, and so a node is created, and also a relationship to that node.
The pattern described can also contain values on the node. These are given using the JSON-like prop : <expression> syntax.
Query
START root=node(2) RELATE root-[:X]-(leaf {name:'D'} ) RETURN leaf
Node node connected with the root node has the name D, and so a new node needs to be created to match the pattern.
Relationships created can also be matched on values.
Query
START root=node(2) RELATE root-[r:X {since:'forever'}]-() RETURN r
In this example, we want the relationship to have a value, and since no such relationship can be found, a new node and relationship are created. Note that since we are not interested in the created node, we don’t name it.
Result
r |
---|
1 row |
Nodes created: 1 |
Relationships created: 1 |
Properties set: 1 |
1 ms |
|
The pattern described by RELATE
can be separated by commas, just like in MATCH
and CREATE
Query
START root=node(2) RELATE root-[:FOO]->x, root-[:BAR]->x RETURN x
This example pattern uses two paths, separated by a comma.
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