Rails Lambda ActiveRecord

Question

I am trying to implement a lambda within a where() method in an ActiveRecord on Rails. Here is my code:

 @applications.where { |app| !((calculate_days_ago(app.shipping_date) >= 10 && calculate_days_ago(:app.shipping_date) <= 19) || app.followup_calls.count == 0) }

Where @applications is an ActiveRecord (e.g. Application.all). But when I am trying to access it (e.g. order, where), it's type is change to WhereChain and I am having an exception:

undefined method `where' for #ActiveRecord::QueryMethods::WhereChain:0x6fb1000>

Is there a way I can implement a lambda expression on my where() condition with the proper return type?

Note: I came from a C# background and such lambda can be done like that, I am a newbie on Ruby on Rails. I am not aware that this community bash newbies with downvotes. I tried my best to make my question as clear as possible.

How are you passing block to `#where` ? I never saw such in documentation. Link please — Arup Rakshit, Feb 23 '15 at 09:29
What is `@applications?` Normally you would call `.where` on the class, eg `Application.where( ....` — Max Williams, Feb 23 '15 at 09:29
@JohnIsaiahCarmona you can pass a block to any method, but it is ignored unless the method calls the block. — Stefan, Feb 23 '15 at 09:42
@MaxWilliams `@applications` is an `ActiveRecord` like `Application.all` — John Isaiah Carmona, Feb 23 '15 at 09:44
@Stefan Thanks for the info. I am a newbie in Rails (coming from a C# background). Is there a way to implement what I am trying to do though? — John Isaiah Carmona, Feb 23 '15 at 09:52

score 3 · Accepted Answer · answered Feb 23 '15 at 09:53

3

The where method doesn't take (or at least it won't use) any block passed to it. If you want to filter based on arbitrary ruby code, then use

@applications.select {|app| !((calculate_days_ago(app.shipping_date) >= 10 && calculate_days_ago(:app.shipping_date) <= 19) || app.followup_calls.count == 0) }

Be aware though that this fetches all the rows matching any previous conditions on the scope, creates active record objects from them and then filters them - if possibly it will in general be a lot faster to rewrite this to use where e.g.

@applications.where(:shipping_date => (19.days.ago .. 10.days.ago))

In addition this keeps things as a relation so you can continue to chain extra where, order etc. calls.

answered Feb 23 '15 at 09:53

Frederick Cheung

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Thanks, but the `select` return an `Array` and I am unable to use `where` on it. Does your second example translate to "Shipping Date is between 10 to 19 days ago"? – John Isaiah Carmona Feb 23 '15 at 09:58
@john It does indeed. – Frederick Cheung Feb 23 '15 at 10:00
Many thanks! Do you know a way to implement my second condition (`app.followup_calls.count == 0`)? I have a one-to-many relationship to the `followup_calls` table and I need to know if it has no followup-call? – John Isaiah Carmona Feb 23 '15 at 10:03
@john either use a counter cache on the association (so that there is just an integer column you can filter on) or a left join. Lots of questions here about that specific type of query – Frederick Cheung Feb 23 '15 at 11:07

Rails Lambda ActiveRecord

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