在这里，我已经收集了十大最未被充分利用的关系方法从该列表中您的阅读喜悦。
10. first_or_create
使用 first_or_create
Book.where(:title => 'Tale of Two Cities').first_or_create
通常情况下，你想找到一个记录的某些属性，或创建一个与这些附加属性。要做到这一点简洁，您可以提供一个块
Book.where(:title => 'Tale of Two Cities').first_or_create do |book| book.author = 'Charles Dickens' book.published_year = 1859 end
9. first_or_initialize
如果不想创建记录属性可以使用
Book.where(:title => 'Tale of Two Cities').first_or_initialize
8. scoped
有时候如果你想查找一个类的记录，你可以使用scoped
def search(query)
if query.blank?
scoped
else
q = "%#{query}%"
where("title like ? or author like ?", q, q)
end
end
7. none (rails
4 中才有)
同样，有时你想要一个ActiveRecord::Relation，不包含任何对象。返回一个空数组通常不是一个好主意，如果你的API的消费者预期的关系对象。相反，你可以使用没有。
def filter(filter_name)
case filter_name
when :all
scoped
when :published
where(:published => true)
when :unpublished
where(:published => false)
else
none
end
end
6. find_each
将所有的数据一次性加载到内存中处理。但是当我们的Model中table数据过多时，会引起程序崩溃。所以，find_each 方法应运而生
find_each方法，是一次性加载1000条(默认)记录到内存中处理，知道将所有数据都处理完
Book.where(:published => true).find_each do |book|
puts "Do something with #{book.title} here!"
end
5. to_sql and explain
关系查询Library.joins(:book).to_sql
Libray.joins(:book).explain
4. find_by (rails
4 中才有)
如可以把
Book.where(:title => 'Three Day Road', :author => 'Joseph Boyden').first
转为
Book.find_by(:title => 'Three Day Road', :author => 'Joseph Boyden')
3. scoping
Comment.where(:post_id => 1).scoping do Comment.first # SELECT * FROM comments WHERE post_id = 1 end
2. pluck
published_book_titles = Book.published.select(:title).map(&:title)
published_book_titles = Book.published.map(&:title)
published_book_titles = Book.published.pluck(:title)
1. merge
class Account < ActiveRecord::Base
# ...
# Returns all the accounts that have unread messages.
def self.with_unread_messages
joins(:messages).merge( Message.unread )
end
end
http://blog.mitchcrowe.com/blog/2012/04/14/10-most-underused-activerecord-relation-methods/