Having trouble with named_scopes for my view

rubyonrails-talk
1

In my articles model, I created a scope that links categories to their respective articles posts. When I use the rails console, the method works perfectly when I query the db.

article.rb

scope :category_technology, -> {where(category_id: 1)}

@articles.category_technology Article Load (0.5ms) SELECT "articles".* FROM "articles" WHERE "articles"."category_id" = ? ORDER BY "articles"."created_at" DESC [["category_id", 1]]

Which works.

2

In my articles model, I created a scope that links categories to their respective articles posts. When I use the rails console, the method works perfectly when I query the db.

article.rb

scope :category_technology, -> {where(category_id: 1)}

@articles.category_technology Article Load (0.5ms) SELECT "articles".* FROM "articles" WHERE "articles"."category_id" = ? ORDER BY "articles"."created_at" DESC [["category_id", 1]]

Which works.

Is that not just the same as @category.articles assuming that @category has id 1

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The problem is that I'm unable to use it in the view and iterate over the records with category_id: 1.

What I'd like to do is something like this technology_controller.rb

def index @technology_articles = Article.category_technology.all.limit(10).last

Again, you would be better to do it the other way around, start with the category and get the articles from that. Note, however that as you have coded it you have specifed .last which means that @technology_articles is only one article, not a collection.

end

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In the index.html.erb

<% if @technology_articles.present? %> <% @technology_articles.each do |article| %> <- omitted -> <% end %>

I'm getting undefined method `each' for #<Article:0x8300868>

That is because you only have a single Article, not a collection, see above.

Colin

3

Colin Law wrote in post #1182073:

4

The limit(10) gives you the first ten records, but since you have ordered descending that means you will get the ten with the highest created_at. Although default_scope sounds like a good idea I have several times used it only to find that it causes confusion and now avoid it. Preferring to explicitly specify the order whenever it matters (via named scopes if appropriate).

Colin

5

Colin Law wrote in post #1182073:

"articles"."category_id" = ? ORDER BY "articles"."created_at" DESC [["category_id", 1]]

I'm getting undefined method `each' for #<Article:0x8300868>

That is because you only have a single Article, not a collection, see above.

Colin

Thanks for responding Colin, I didn't realize .last would lead to a single article being queried. I thought it would give me the last 10 records. I guess DESC being my default named_scope: default_scope -> { order(created_at: :desc) } should take care of that for me. Thanks.

The limit(10) gives you the first ten records, but since you have ordered descending that means you will get the ten with the highest created_at. Although default_scope sounds like a good idea I have several times used it only to find that it causes confusion and now avoid it. Preferring to explicitly specify the order whenever it matters (via named scopes if appropriate).

Part of one of the RailsConf sessions I went to, either last year or the year before, could have been re-titled "default_scope considered harmful". I don't think it's deprecated or anything, but it is definitely something to use sparingly, and with a lot of forethought about what other scopes you may need later. Better to chain scopes, so you call ControllerName.your_scope.latest, rather than adding the "latest" behavior into your default scope. It makes it more declarative. More (duplicated) characters is not really the issue you want to prioritize. Being able to reason about your code in the current bit you are working on is.

Walter

6

Walter Davis wrote in post #1182112:

Part of one of the RailsConf sessions I went to, either last year or the year before, could have been re-titled "default_scope considered harmful". I don't think it's deprecated or anything, but it is definitely something to use sparingly, and with a lot of forethought about what other scopes you may need later. Better to chain scopes, so you call ControllerName.your_scope.latest, rather than adding the "latest" behavior into your default scope. It makes it more declarative. More (duplicated) characters is not really the issue you want to prioritize. Being able to reason about your code in the current bit you are working on is.

Walter

Very true. Thank you for your advice.