Suppose we have
User
name
: StringTransaction
amount
: Floatrepresenting a simplized Bitcoin-like transaction, where a User sends coins to other Users. A Transaction has a property amount
which shows how much coin you're sending to the to_node
from from_node
.
Then now I want to get all the transactions (either uni- or bi- directionally) between Alice and Bob. How can I do this?
# user.rb
has_many :out, :receivers, rel_class: :Transaction
has_many :in, :senders, rel_class: :Transaction
# Console
alice = User.find_by(name: "Alice")
bob = User.find_by(name: "Bob")
# I want to do something like this:
Transaction.between(from: alice, to: bob)
# or this:
alice.receivers.rel_where(to_node: bob)
I was surprised that the latter isn't acceptable. It includes bob
directly into CYPHER.
Using Neo4jrb v8.0.0
I struggled and came to know I can do something like this:
alice.receivers.match_to(bob).pluck(:rel1)
With this we can get all the transactions sent from alice
to bob
, but I think it's not a good idea using the magical :rel1
here (which is available because it is automatically written in the CYPHER, and match_to
returns a QueryProxy
object: match_to
)
But it is always not much encouraged to get just the Rels.
Relatively, we could
alice.receivers.match_to(bob).rel_where(amount: 1.0) # Txs which amount are 1.0btc
and
alice.receivers.match_to(bob).each_rel.sum {|rel| rel.amount } # All the sent money!
ć
Note that you can't do this (somehow):
alice.receivers.match_to(bob).rel_where("rel1.amount < 10.0")
but can go-around with this:
query = alice.receivers.match_to(bob) # create just the query
query.where("#{query.rel_var}.amount < 10.0") # you can get `:rel1` by `rel_var`