Provide saveAs overloads with a predicate for selecting projected attributes.

[michael-simons]

This implements #2420. Please @Andy2003 check if this suites your needs.

Before you ask: Chances are minimal to have something similar for reading. For read it just feels like the wrong approach. If we are down there, one might ask for the relevance of the mapping process itself and just delegate to the client.

Thanks @meistermeier for your help on this. I did not touch anything that might be affected by spring-projects/spring-data-commons#2420

Funny coincidence that those things have the same issue number :D

[meistermeier]

Given this call and the current usage looks like new PropertyTraverser(..).traverse(..) wouldn't it make sense to make those methods static?

[michael-simons]

No. The thing has state.

[meistermeier]

Since we accept it, the instance should be @Nullable. Would also make sense for the saveAllAs method and the reactive counter-parts. (Would need an additional null check in the saveAllAs/saveAllImpl).

[Andy2003]

Given

Node node2 = Node.builder()
		.name("test123")
		.parent(rootNode) // rootNode was queried before
		.build();

neo4jTemplate.saveAs(node2, (propertyPath, property) -> {
	if (propertyPath.stream().count() > 1){
		// do not save deeper than level 1
		return false;
	}
	if (!property.isRelationship()) {
		return true;
	}
	return property.getName().equals("parent");
});

3 write queries are triggered:

1. the merge of the newly created node including its properties to save RUN "MERGE (node:Node {nodeId: $__id__}) SET node += $__properties__ RETURN node" {__id__="5dca7a8c-8f5e-4089-aae5-5e794332b7c0", __properties__={name: "test123", nodeId: "5dca7a8c-8f5e-4089-aae5-5e794332b7c0", created: NULL}}
2. a non required update of the root node MERGE (node:Node {nodeId: $__id__}) SET node += $__properties__ RETURN node" {__id__="root", __properties__={}}
3. The creation of the relation: MATCH (startNode:Node) WHERE startNode.nodeId = $fromId MATCH (endNode) WHERE id(endNode) = $toId MERGE (startNode)-[relProps:CHILD_OF]->(endNode) RETURN id(relProps)" {toId=40, __knownRelationShipId__=NULL, fromId="5dca7a8c-8f5e-4089-aae5-5e794332b7c0"}

The 2nd query should be filtered out

[meistermeier]

Sorry for the late reply. Could you please describe why you explicitly add parent to the list but on the other hand say SDN should not persist it.
I agree, on a technical level saving a node without properties does not make any sense at first sight. But this needs also be done if e.g. the root node is a new node.

[Andy2003]

With parent I meant that the relation should be stored. But I don`t want to change any properties at the parents node.

[meistermeier]

I would like to keep this out of this PR.
I am not yet convinced that we would ever make a difference between the relationship and the relationship with a related node in the future.

[meistermeier]

Merged with f79ad5393a9f9a54ec800f00a71b3a87a8c257e4