Neo4J MERGE support

[sheerun]

MERGE is introduced in Neo4j 2. Will this gem support it?

[andreasronge]

why not,
How would you like the DSL to look like for merge ?

[sheerun]

For nodes:

Neo4j.merge(id: 12).on_create(name: 'John').on_match(updated_at: 'timestamp()')

For relationships:

Neo4j.merge_path { |n| n > rel(:friends) > node(2) }

Btw. documentation for Neo4j.create is in wrong place (With):
https://github.com/andreasronge/neo4j/wiki/Neo4j%3A%3ACypher-With

[OpenCoderX]

How would I pass a label?

[sheerun]

The same way as create

Neo4j.merge({ id: 12 }, :foobar)

[andreasronge]

Hmm, how about something like this:

merge{node.create({ id: 12 }, :foobar)}

Then a DSL for merge on multiple relationship would be similar:

Example:

merge do
   match({name:'Oliver Stone'}, :Person) >  "movie:Movie" > match({name:'Rob Reiner'}, :Person)
end
ret(:movie)

generates cypher:

MATCH (oliver:Person { name:'Oliver Stone' }),(reiner:Person { name:'Rob Reiner' })
MERGE (oliver)-[:DIRECTED]->(movie:Movie)<-[:ACTED_IN]-(reiner)
RETURN movie

[sheerun]

I don't think matches should be nested in merge, because they are in no way local to it. On the other hand on_create and on_match make sense only in context of merge.

Probably following makes more sense:

oliver = match({name:'Oliver Stone'}, :Person)
rob = match({name:'Rob Reiner'}, :Person)
merge(oliver >  "movie:Movie" > rob)

And for nodes:

merge({name:'Oliver Stone'}, :Person) do
  on_match(age: '12')
  on_create(created_at: 'timestamp()')
end

which is the same as:

merge(oliver >  "movie:Movie" > rob).on_create(...).on_match(...)
merge({name:'Oliver Stone'}, :Person).on_create(...).on_match(...)

So generally merge could accept either node or relationship to match, and the on_match and on_create could be defined in block or chained syntax.

[sheerun]

Even better:

match({name:'Oliver Stone'}, :Person).as(:oliver)
match({name:'Rob Reiner'}, :Person).as(:rob)
merge(:oliver > "movie:Movie" > :rob)
ret(:movie)

[andreasronge]

That is actually the same as

merge do
   match({name:'Oliver Stone'}, :Person) >  "movie:Movie" > match({name:'Rob Reiner'}, :Person)
end
ret(:movie)

except that the names of the nodes (oliver and rob is generated for you).
So if we implement the syntax above then it is also possible to express it as you suggested

[sheerun]

In your case marge expects block it's yielding to return matched relation.

I think it makes more sense to accept this relation as argument. For example it's rather unclear that in example below second match is passed to merge while first match is free-standing.

merge do
   some_guy = match({name:'Rob Reiner'}, :Person)
   match(some_guy > ":friend_of" > :person)
   match({name:'Oliver Stone'}, :Person) > "movie:Movie" > :person
end

When using nested match, you cannot support multiple matches anyway, so what's the advantage? I'm not sure about this.

[sheerun]

I fixed syntax, but probably it's messed up anyway. I'm no expert in neo4j-cypher.