I need to return exactly ten records for use in a view. I have a highly restrictive query I'd like to use, but I want a less restrictive query in place to fill in the results in case the first query doesn't yield ten results.
Just playing around for a few minutes, and this is what I came up with, but it doesn't work. I think it doesn't work because merge is meant for combining queries on different models, but I could be wrong.
class Article < ActiveRecord::Base
...
def self.listed_articles
Article.published.order('created_at DESC').limit(25).where('listed = ?', true)
end
def self.rescue_articles
Article.published.order('created_at DESC').where('listed != ?', true).limit(10)
end
def self.current
Article.rescue_articles.merge(Article.listed_articles).limit(10)
end
...
end
Looking in console, this forces the restrictions in listed_articles on the query in rescue_articles, showing something like:
Article Load (0.2ms) SELECT `articles`.* FROM `articles` WHERE (published = 1) AND (listed = 1) AND (listed != 1) ORDER BY created_at DESC LIMIT 4
Article Load (0.2ms) SELECT `articles`.* FROM `articles` WHERE (published = 1) AND (listed = 1) AND (listed != 1) ORDER BY created_at DESC LIMIT 6 OFFSET 4
I'm sure there's some ridiculously easy method I'm missing in the documentation, but I haven't found it yet.
EDIT: What I want to do is return all the articles where listed is true out of the twenty-five most recent articles. If that doesn't get me ten articles, I'd like to add enough articles from the most recent articles where listed is not true to get my full ten articles.
EDIT #2: In other words, the merge method seems to string the queri开发者_JS百科es together to make one long query instead of merging the results. I need the top ten results of the two queries (prioritizing listed articles), not one long query.
with your initial code:
You can join two arrays using + then get first 10 results:
def self.current
(Article.listed_articles + Article.rescue_articles)[0..9]
end
I suppose a really dirty way of doing it would be:
def self.current
oldest_accepted = Article.published.order('created_at DESC').limit(25).last
Artcile.published.where(['created_at > ?', oldest_accepted.created_at]).order('listed DESC').limit(10)
end
If you want an ActiveRecord::Relation
object instead of an Array, you can use:
ActiveRecordUnion gem.
Install gem:
gem install active_record_union
and use:def self.current Article.rescue_articles.union(Article.listed_articles).limit(10) end
UnionScope module.
Create module UnionScope (lib/active_record/union_scope.rb).
module ActiveRecord::UnionScope def self.included(base) base.send :extend, ClassMethods end module ClassMethods def union_scope(*scopes) id_column = "#{table_name}.id" if (sub_query = scopes.reject { |sc| sc.count == 0 }.map { |s| "(#{s.select(id_column).to_sql})" }.join(" UNION ")).present? where "#{id_column} IN (#{sub_query})" else none end end end end
Then call it in your Article model.
class Article < ActiveRecord::Base include ActiveRecord::UnionScope ... def self.current union_scope(Article.rescue_articles, Article.listed_articles).limit(10) end ... end
All you need to do is sum the queries:
result1 = Model.where(condition)
result2 = Model.where(another_condition)
# your final result
result = result1 + result2
I think you can do all of this in one query:
Article.published.order('listed ASC, created_at DESC').limit(10)
I may have the sort order wrong on the listed column, but in essence this should work. You'll get any listed items first, sorted by created_at DESC, then non-listed items.
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