Rails中scopes的几种使用方法

不传参数使用scope方法
class User < ActiveRecord::Base
scope :finduser, {where(status: 'username')}
scope :has_content, {joins(:comment).where("comments.content is not null")}
end



传参数使用scope方法

class User < ActiveRecord::Base
scope :finduser, ->(username){ where(username: username) }
scope :has_content, ->(content){joins(:comment).where('comments.content = ?', content)}
end

class User < ActiveRecord::Base
scope :finduser, Proc.new { |username| where(username: username) }
scope :has_content, Proc.new{joins(:comment).where('comments.content = ?', content)}
end

class User < ActiveRecord::Base
scope :finduser, lambda { |username| where(username: username) }
scope :has_content, lambda{joins(:comment).where('comments.content = ?', content)}
end

class User < ActiveRecord::Base
def self.finduser username
where(username: username) unless username.empty?
end

def self.has_content content
lambda{joins(:comment).where('comments.content = ?', content)}
end
end

总结

当逻辑是简单的where/order这样的查询时使用scope；涉及到复杂查询时，使用类方法。
另外，当需要做一些扩展时，作为Active Record提供的一个特性，我还是推荐使用scope。