Working with Relationships in Rails

[CLG]

Intense beginner question here but I've been unable to find the answer anywhere.

I have model, show.rb:

class Show < Neo4j::Rails::Model

    property :show_name, type: String, index: :exact

    has_n :booked_bands

end

I have another model, band.rb

class Band < Neo4j::Rails::Model

    property :band_name, type: String, index: :exact

    has_n :playing_shows

end

I create a show.

show = Show.new

show.show_name = "Test Show"

show.save

I create a band.

band = Band.new

band.band_name = "MyBand"

band.save

I create a relationship by which the band is playing the show:

band.playing_shows << show

band.save

The crux of my question: how do I access the band object's properties when I retrieve it from the show?

Whenever I try to do something like this:

theshow = band.playing_shows

I get a response like this:

=> #<Neo4j::Rails::Relationships::NodesDSL:0x39fe9ce1 @dir=:outgoing, @storage=#<Neo4j::Rails::Relationships::Storage:0xcb5efc8 @rel_class=Neo4j::Rails::Relationship, @target_class=Neo4j::Rails::Model, @incoming_rels=[], @node=#<Band:0x3adcbf25 @errors=#<ActiveModel::Errors:0x57f9cc39 @base=#<Band:0x3adcbf25 ...>, @messages={}>, @_relationships={:playing_shows=>#<Neo4j::Rails::Relationships::Storage:0xcb5efc8 ...>}, @_properties={"band_name"=>"MyBand", "_classname"=>"Band"}, @changed_attributes={}, @_create_or_updating=nil, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x3fd3659b>, @previously_changed={}, @_properties_before_type_cast={:band_name=>"MyBand"}, @validation_context=nil>, @rel_type=:playing_shows, @persisted_related_nodes={:outgoing=>[#<Show:0x50d8dc5a @_relationships={}, @_properties={}, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x258e4566>, @_properties_before_type_cast={}>]}, @outgoing_rels=[], @persisted_relationships={}, @persisted_node_to_relationships={:outgoing=>{#<Show:0x50d8dc5a @_relationships={}, @_properties={}, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x258e4566>, @_properties_before_type_cast={}>=>#<Java::OrgNeo4jKernelImplCore::RelationshipProxy:0x349319f9>}}>>

If I do this:

theshow = band.playing_shows.to_a

I get this, which looks more manageable:

=> [#<Show:0x50d8dc5a @_relationships={}, @_properties={"show_name"=>"Test Show"}, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x258e4566>, @_properties_before_type_cast={}>]

This looks like it is referring to my test show as expected.

but then when try "theshow.show_name" I receive "NoMethodError: undefined method `show_name' for #<Array:0x14eebce6>"

If I try to loop through it like this:

theshow.each do |s|

  s.show_name

end

I get this:

=> [#<Show:0x50d8dc5a @_relationships={}, @_properties={"show_name"=>"Test Show"}, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x258e4566>, @_properties_before_type_cast={}>]

How do I get JUST "Test Show" to output? I can't find any sample apps that really show me and I'm too green to make full sense of the documentation. It seems so simple, I'm sure I am doing something wrong.

Any clarification is appreciated.

[Andreas Ronge]

Hi

Since you have declared a has_n relationship you will get a Ruby Enumerable (which the Neo4j::Rails::Relationship has mixed in) of Node objects when you use the

playing_shows accessor method.

So, if you want to look at the first show node object you simply use the .first method (just as you would like on an array) on the enumerable.

  theshow = band.playing_shows.first

Notice you can also declare a has_one relationship.

See Gist:

https://gist.github.com/andreasronge/5433066

Cheers

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[CLG]

Excellent! Thank you. Got it, I was over-thinking... or maybe under-thinking. ;-)

My model now looks like this:

class Show < Neo4j::Rails::Model

  property :show_name,        type: String, index: :exact

  has_n(:bands).from(Band, :playing_show)

end

class Band < Neo4j::Rails::Model

  property :band_name,        type: String, index: :exact

  has_n(:playing_show).to(Show)

end

When I go to an individual Show node's page and try to view all Bands appearing:

<% @show.bands.each do |b| %>

  <%= b.band_name %><br />

<% end %>

It returns:

Band1
Band2
[#<Band:0x2be040e5 @_properties_before_type_cast={}, @_relationships={}, @_properties={"band_name"=>"Band1"}, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x199c36ee>>, #<Band:0x418b04a5 @_properties_before_type_cast={}, @_relationships={}, @_properties={"band_name"=>"Band2"}, @_java_node=#<Java::OrgNeo4jKernelImplCore::NodeProxy:0x6a20cc11>>]

The problem, of course, being the block after the band names. When I go in the opposite direction, using "@band.playing_shows.each" while trying to see all Shows that a band is playing (instead of all bands playing a show) it does not append the additional relationship data.

[Andreas Ronge]

Hi

Sorry, I don't understand the problem. The block after the band names is strange, maybe you have set the band_name to the string "[#<Band: ..." ?

What do you man with not appending additional relationship data ?

Can you try with a clean database ?

Cheers

--

[CLG]

That was my very awkward way of saying "What's the deal with all the '[#<Band: ...' stuff?" Answer was that it was a new-to-Rails thing. I was using <%= in a view, should have been <%. Amateur hour.

<% @show.bands_playing.each do |b| %>

  <%= b.band_name %><br />

<% end %>

Here is a Gist of the entire thing with examples of accessing the relationship from each direction in case someone else wants more examples. https://gist.github.com/subvertallchris/30c334854be70f1a9ea0

Thanks for the help!

Chris