Thank you so much!
You're a fantastic reader, and really got what we were trying to do.
For now, we're happy with eager_graph- but your point is well heeded and
we'll investigate the alternate output needed for csv.
We are primarily building a JSON web service on Sinatra, so for now this
will be fine.
Once we wrapped our heads around the semantics of the model- we realise how
powerful it is, and how accessible it is.
Thank you! a truly great library- appreciate all your help Jeremy :)
Dean + Adarsh
On Friday, 6 June 2014 13:09:15 UTC+10, Jeremy Evans wrote:
>
> On Thursday, June 5, 2014 7:30:17 PM UTC-7, Dean Cornish wrote:
>>
>> Hi All,
>>
>> My dev pair and I are struggling a little bit-
>> See attached.
>> We can successfully navigate up and down on either side eg. App -> IR ->
>> Depl and back again using:
>>
>> Given a Model structure of:
>>
>> class Application < Sequel::Model
>> many_to_many :irs
>> end
>>
>> class Ir< Sequel::Model
>> many_to_many :applications
>> many_to_many :releases
>> many_to_many :deployments
>> end
>>
>> class Release < Sequel::Model
>> many_to_many :irs
>> end
>>
>> class Deployment < Sequel::Model
>> many_to_many :irs
>> end
>>
>>
>> #this returns everything linked from a releases up the chain in reverse
>> Application.eager_graph(:irs => :releases).each {
>> |t| puts "Applications down through to Releases: #{t.inspect}\n"
>> }
>>
>> and
>>
>> #this returns everything linked from a release up the chain in reverse
>> Release.eager_graph(:irs => :applications).each {
>> |t| puts "Release up through to Applications: #{t.inspect}"
>> }
>>
>> We can trivially modify the above to traverse Deployments and
>> Applications in both directions.
>>
>> The issue- if you can help us- is with how do we have a single query that
>> returns Application -> Irs and both Releases and Deployments something like:
>>
>> This is of course- fantasy code- but if you can help us to understand
>> what might achieve this kind of outcome - it would be great. We're newbies
>> with sequel :)
>>
>> #this returns just the fields we want for csv and other export
>> Application.eager_graph([:irs => :deployments, irs =>
>> releases]).select(:applications__application_name, :irs__ir_name,
>> :releases__release_name, :deployments__deployment_number).each {
>> |t| puts "Applications down via irs to both Release and
>> Deployments: #{t.values}"
>> }
>>
>> Any help you can provide would be awesome :)
>>
>
> You were almost there:
>
> Application.eager_graph(:irs => [:deployments, releases])
>
> Note that you have to use set_graph_aliases instead of select when using
> eager_graph. However, for a csv export, an eager_graph is probably not
> what you want, since eager_graph provides a object graph, and CSV really
> deals best with a table (array of arrays). You probably want to use
> association_join/association_left_join instead of eager_graph for a csv
> export (in which case you can continue to use select, or maybe even
> select_map). For a json export, you would probably want to use eager_graph
> or something similar.
>
> Note that you need to understand what is going on at an SQL level if you
> use eager_graph. With the code given above, you could be generating huge
> results sets due to the cartesian products involved. For example, if you
> were eager loading 100 apps, and each had 100 irs, and each of those irs
> had 100 releases and 100 deployments, you are looking at 100,000,000 rows
> in the returned result set. Unless you are filtering or ordering based on
> columns in the associated table, you are probably better off using eager
> instead of eager_graph.
>
> Thanks,
> Jeremy
>
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