Model name : XXX, :pluralize=>xxxS
Find query:
XXX.find(1) # => select * from XXX where id=1
NOTE: it raise exception when no record found
Better use this one:
XXX.find_by_id(1) #=> Works perfectly without raising andy exception
WHERE clause
XXX.find(:all , :conditions=>['id =?', 1] )
ORDER
XXX.find(:all, :order => "date")
WHERE clause many conditions
XXX.find(:all, :conditions => ['XXX_ID not in (?)', (@xxxS.empty? ? '' : @xxxS.map(&:id))])
Topic.where( 'forum_id not in (?)', (@forums.empty? ? '' : @forums.map(&:id)) ).all
find(:all, :select => "name").map(&:name) # find all records, then map name attributes to an array
SUM
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Grouping with multiple columns cannot be supported by rails. You have to use a regular find all:
budgets = Budgets.find(:all,
:select => "emptype_id, calendar_id, sum(budgets.actual_head) AS sum_actual_head",
:group => "emptype_id, calendar_id")
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Budgets.sum(:actual_head ,:group=>["emptype_id"," calendar_id"] )
'NOT IN' operations
Topic.all - @forums.map(&:id)
Join Operations
Topic.all(:joins => "left join forums on (forums.id = topics.forum_id and some_condition)", :conditions => "forums.id is null")
Deletion of HABTM intersection table
Menus.items.delete( Item.find_by_id(1) ); # ! IMPORTANT
Nested Select Statements
@answers = Answer.select([:id, :content, :points])
.where(question_id: @questions.pluck(:id))
This is the same as:
SELECT id, content, points
FROM answers
WHERE question_id in (<question_ids array>)
References:
http://ar.rubyonrails.org/classes/ActiveRecord/Calculations/ClassMethods.html
