deleting-rels.rb

class Book
  include Neo4j::ActiveNode

  property :title
  has_many :in, :spaces, rel_class: :BookAuthor
end

class Author
  include Neo4j::ActiveNode

  property :first_name
  property :last_name

  has_many :out, :books, rel_class: :BookAuthor
end

class BookAuthor
  include Neo4j::ActiveRel

  from_class :Author
  to_class :Book
  type 'book_author'
  creates_unique_rel
end

# clear out the db
Neo4j::Session.query('START n=node(*) MATCH (n)-[r]->(m) DELETE n,m,r').to_a

a1 = Author.create!(first_name: 'Doubting', last_name: 'Thomas')
a2 = Author.create!(first_name: 'Debbie', last_name: 'Downer')

b1 = Book.create!(title: 'How to lose friends and annoy people')
b2 = Book.create!(title: 'The Art of Foo Bar')

# co-authors...
[a1, a2].each do |a|
  [b1, b2].each do |b|
    rel = BookAuthor.new
    rel.from_node = a
    rel.to_node = b
    rel.save!
  end
end

# a1 is no longer a co-author of b1
count = -> {
  Neo4j::Session.query.
    match('(a)-[r:book_author]->(b)').
    where("ID(a) = ?", a1.neo_id).
    return(:b).
    to_a.length
}

puts "pre-delete: #{count.()}"

del = Neo4j::Session.query.
      match('(a)-[r:book_author]->(b)').
      where("ID(a) = ? AND ID(b) = ?", a1.neo_id, b1.neo_id).
      delete(:r).
      exec

puts "parameterized: #{count.()}"

del = Neo4j::Session.query.
      match('(a)-[r:book_author]->(b)').
      where("ID(a) = #{a1.neo_id} AND ID(b) = #{b1.neo_id}").
      delete(:r).
      exec

puts "interpolated: #{count.()}"