merge

The merge module provides the capabilities of the MERGE Cypher command, merging or creating nodes and relationships as per specified conditions. It ensures precision and coherence in managing interconnected data structures.

Source code

Trait	Value
Module type	util
Implementation	C++
Graph direction	directed/undirected
Edge weights	weighted/unweighted
Parallelism	sequential

Procedures

You can execute this algorithm on graph projections, subgraphs or portions of the graph.

`node()`

The procedure provides a more flexible way of merging nodes than Cypher’s MERGE clause, by allowing labels and properties to be extracted as results of other procedures and sent as a list or map.

Input:

subgraph: Graph (OPTIONAL) ➡ A specific subgraph, which is an object of type Graph returned by the project() function, on which the algorithm is run. If subgraph is not specified, the algorithm is computed on the entire graph by default.
labels: List[string] ➡ A list of all labels that need to be added to the new node.
identProps: Map ➡ A map with key-value pairs used for identifying which nodes will be merged.
createProps: Map ➡ A map with key-value pairs which represent properties of the node, when the procedure creates a new node. Equivalent to using ON CREATE SET for properties when using MERGE.
mergeProps: Map ➡ A map with key-value pairs which represent properties of the node, when the procedure merges onto a node. Equivalent to using ON MATCH SET for properties when using MERGE.

Output:

node: Node ➡ The node which was created or merged in the procedure.

Usage:

Consider a graph with two Human, and one Alien node.

CREATE (h:Human {name:"Mark", age: 20}), (h2:Human {name:"Eva", age: 30}), (a:Alien {name: "Gorlock", age: 20});

Use the merge.node() procedure on all nodes, and add galaxy property on the existing nodes. By leaving labels and identProp empty, all nodes in the graph will be affected by the procedure.

CALL merge.node([],{},{},{galaxy: "Milky way"}) 
YIELD node 
RETURN node;

+----------------------------------------------------------------------------------------------------------------+
| node                                                                                                           |
+----------------------------------------------------------------------------------------------------------------+
| {"id": 0,"labels": ["Human"],"properties": {"age": 20,"galaxy": "Milky way","name": "Mark"},"type": "node"}    |
+----------------------------------------------------------------------------------------------------------------+
| {"id": 1,"labels": ["Human"],"properties": {"age": 30,"galaxy": "Milky way","name": "Eva"},"type": "node"}     |
+----------------------------------------------------------------------------------------------------------------+
| {"id": 2,"labels": ["Alien"],"properties": {"age": 20,"galaxy": "Milky way","name": "Gorlock"},"type": "node"} |
+----------------------------------------------------------------------------------------------------------------+

Now, use the merge.node() procedure to either merge or create an Alien node with the name Zumbi. If that's a newly created node, the age property will be 30, and if it's a merged node, age will be 40. Additionally, the galaxy property will be used as an identifying property.

When using merge.node() procedure or MERGE clause, if there is no match in the graph, and a node is created, it will be created with identifying properties alongside create properties defined by the createProps input parameter.

CALL merge.node(["Zumbi"],{galaxy: "Andromeda"},{age:20},{age: 40}) 
YIELD node 
RETURN node;

+----------------------------------------------------------------------------------------------------------------+
| node                                                                                                           |
+----------------------------------------------------------------------------------------------------------------+
| {"id": 3,"labels": ["Zumbi"],"properties": {"age": 20,"galaxy": "Andromeda"},"type": "node"}                  |
+----------------------------------------------------------------------------------------------------------------+

A new node was created, because the graph did not contain an Alien node with the name `Zumbi.

Now, use the merge.node() procedure to give weapons to all Humans aged 20.

CALL merge.node(["Zumbi"],{galaxy: "Andromeda"},{age:20},{age: 40}) YIELD node RETURN node;

+---------------------------------------------------------------------------------------------------------------------------------+
| node                                                                                                                            |
+---------------------------------------------------------------------------------------------------------------------------------+
| {"id": 0,"labels": ["Human"],"properties": {"age": 20,"galaxy": "Milky way","name": "Mark","weapon": "sword"},"type": "node"}  |
+---------------------------------------------------------------------------------------------------------------------------------+

Mark is the only node on the graph that can get a weapon property.

Finally, let's age every 20-year-old to 25.

CALL merge.node([],{age: 20},{},{age: 25}) YIELD node RETURN node;

+---------------------------------------------------------------------------------------------------------------------------------+
| node                                                                                                                            |
+---------------------------------------------------------------------------------------------------------------------------------+
| {"id": 0,"labels": ["Human"],"properties": {"age": 25,"galaxy": "Milky way","name": "Mark","weapon": "sword"},"type": "node"}   |
+---------------------------------------------------------------------------------------------------------------------------------+
| {"id": 2,"labels": ["Alien"],"properties": {"age": 25,"galaxy": "Milky way","name": "Gorlock"},"type": "node"}                  |
+---------------------------------------------------------------------------------------------------------------------------------+
| {"id": 33,"labels": ["Zumbi"],"properties": {"age": 25,"galaxy": "Andromeda"},"type": "node"}                                   |
+---------------------------------------------------------------------------------------------------------------------------------+

`relationship()`

The procedure provides a more flexible way of merging relationships than Cypher’s MERGE clause, by allowing labels and properties to be extracted as results of other procedures and sent as a list or map.

Input:

startNode: Node ➡ The start node of the relationship.
relationshipType: string ➡ The relationship type to be matched or created.
identProps: Map ➡ A map with key-value pairs used for identifying which relationships will be merged.
createProps: Map ➡ A map with key-value pairs which represent properties of the relationship, when the procedure creates a new relationship. Equivalent to using ON CREATE SET for properties when using MERGE.
endNode: Node ➡ The end node of the relationship.
mergeProps: Map ➡ A map with key-value pairs which represent properties of the relationship, when the procedure merges onto a relationship. Equivalent to using ON MATCH SET for properties when using MERGE.

Output:

rel: Relationship ➡ The relationship which was created or merged in the procedure.

Usage:

Consider a graph with one Human, two Dog nodes. Both dogs love the human but one loves him unconditionally.

CREATE (d:Dog {name: 'Johnny'})-[l:Loves {unconditionally: true}]->(h:Human)
CREATE (c:Dog {name: 'Floki'});

Use merge.relationship() procedure to add a property called trueLove to every Loves relationship between a human and a dog that has the property unconditional set to true. Otherwise, create a new Loves relationship with the property unconditionally set to false.

MATCH (d:Dog)
MATCH (h:Human) 
CALL merge.relationship(d, 'Loves', {unconditionally: true}, {unconditionally: false}, h, {trueLove: true}) 
YIELD rel;

+---------------------------------------------------------------------------------------------------------------------------+
| rel                                                                                                                       |
+---------------------------------------------------------------------------------------------------------------------------+
| {"id":1,"start":3,"end":4,"label":"Loves","properties":{"trueLove":true,"unconditionally":true},"type":"relationship"}    |
+---------------------------------------------------------------------------------------------------------------------------+
| {"id":2,"start":5,"end":4,"label":"Loves","properties":{"unconditionally":false},"type":"relationship"}                   |
+---------------------------------------------------------------------------------------------------------------------------+