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Rails是如何访问一个系列中的前一个记录的?

ruby-on-rails-2 rails-activerecord ruby-on-rails

nfm · 技术社区 · 14 年前

说我有一个 Statement 模型,其中 has_many :months 第一个月可能不同 (例如月数=[三月、四月、五月…一月、二月])

给定一个月,MVC如何找到前一个月?

我发现自己通过 statement 感觉脏兮兮的:

# statement.rb
has_many :months

def previous_month(month)
  if months.index(month) == 0
    return nil
  else
    return months[months.index(month) - 1]
  end
end

# blergh
prev_month = month.statement.previous_month(month)

previous_month_id 数据库中的列?您将如何实现此功能?我在用铁轨 2.3.x .

3 回复 | 直到 11 年前

edgerunner 14 年前

我会在 Month 减少往返旅行的模式。

# month.rb
class Month < ActiveRecord::Base
  belongs_to :statement, :include => :months

  def previous
    return nil if self.index == 0
    find_or_create_by_index_and_statement_id(self.index - 1, self.statement.id)
  end

  def index
    statement.months.index self
  end
end

这样你就可以 june.previous

mark 14 年前

这些月是怎么加的?如果它们是按照月份的时间顺序单独添加的,那么您可以简单地执行已有的操作,但是您应该定义关系中的顺序。

#statement.rb

has_many :months, :order => 'created_at ASC'

如果它们是以其他方式添加的,那么您可能需要考虑使用order列和 acts_as_list 维持秩序。

Jed Schneider 14 年前

created_at 你能绑在柱子上吗?这是我想出来的,可能对你没有帮助。尽管结帐 Date::MONTHNAMES 至少听起来这对你有帮助。

describe User do
  before(:each) do
    @user = User.create!
  end

  it "should know about months" do
    Statement.create(:user => @user)
    @user.statements.last.month_name.should == "November"
  end

  it "should report last months statement as nil when there is no statement" do
    @user.last_months_statement.should be_nil
  end

  it "should report last months statement as nil if there is only one for this month" do
    Statement.create(:user => @user)
    @user.last_months_statement.should be_nil
  end

  it "should report a statement from the previous month if there is one"  do
    target = Statement.create(:user => @user, :created_at => 1.month.ago)
    Statement.create(:user => @user)
    @user.last_months_statement.should == target
  end

  it "should report last months statement if there a several" do
    Statement.create(:user => @user, :created_at => 1.month.ago)
    Statement.create(:user => @user)
    Statement.create(:user => @user, :created_at => 2.months.ago)
    @user.last_months_statement.month_name.should == "October"
  end
end

class User < ActiveRecord::Base
  has_many :statements, :order => "created_at"

  def last_months_statement
    if statements.size <= 1 || statements.last.created_at.month < Time.now.month
      nil
    else
      index = statements.index(statements.last)
      statements[index - 1]
    end
  end
end

class Statement < ActiveRecord::Base
  belongs_to :user

  def month
    created_at.month
  end

  def month_name
    Date::MONTHNAMES[created_at.month]
  end
end