如何简化大条件

首先,你的一些逻辑没有道理:

def search(search, compare, year, rain_fall_type)
  if search == 'All'
    if rain_fall_type == 'All'
      all
    else
      # rain_fall_type != 'All'
      if year == 'All'
        if rain_fall_type == "None"
          where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
        else
          where(Sector: rain_fall_type).order('id')
        end
      else
        # in rain_fall_type != 'All' branch, so meaningless 'if'
        if rain_fall_type == "All"
          order("#{year} ")
        elsif rain_fall_type == "None"
          where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
        else
          where(Sector: rain_fall_type).order("#{year} ")
        end
      end
    end
  elsif compare != "None"
    # both are same, so meaningless 'if'
    if year == 'All'
      where('Sector = ? OR Sector = ?', rain_fall_type, compare).order(:id)
    else
      where('Sector = ? OR Sector = ?', rain_fall_type, compare).order(:id)
    end
  else
    # search != 'All'
    if rain_fall_type == 'All'
      all.order('id')
    else
      if year == 'All'
        if rain_fall_type == "None"
          where('Sector = ? ', search).order('id')
        else
          where('Sector = ? ', rain_fall_type).order('id')
        end
      else
        if rain_fall_type == "None"
          # in search != 'All' branch, so meaningless 'if'
          # AND both are same, so again meaningless 'if'
          if search == "All"
            where('Sector = ? ', search).order('id')
          else
            where('Sector = ? ', search).order('id')
          end
        else
          where('Sector = ? ', rain_fall_type).order('id')
        end
      end
    end
  end
end

还有更多类似的事情,我不会一一指出,因为我们都在扔这些东西 if

最终,我们将把查询推迟到方法的末尾,如下所示:

def search(search, compare, year, rain_fall_type)

  ...

  @query = all 
  @query = @query.where(Sector: @sectors) if @sectors
  @query = @query.order(@order) if @order
  @query

end

这样,你就可以 where 和 order 最后只做一次。这样就省去了大量的打字。请参阅muistooshort的评论了解原因 (Sector: @sectors) 作品。

@sectors 和 @order . 首先,我将把输入变量赋给实例变量,因为我喜欢这样(并避免变量之间的混淆) @search search ):

def search(search, compare, year, rain_fall_type)
  @search, @compare, @year, @rain_fall_type = search, compare, year, rain_fall_type

  ...

  @query = all 
  @query = @query.where(Sector: @sectors) if @sectors
  @query = @query.order(@order) if @order
  @query
end

现在,这个答案已经持续太久了,所以我不会把你拖到所有血淋淋的细节。但是,添加几个helper方法( sectors_to_use order_to_use )用它们来代替 @部门 和 ,你基本上会得到这样的结果:

def search(search, compare, year, rain_fall_type)
  @search, @compare, @year, @rain_fall_type = search, compare, year, rain_fall_type
  @query = all 
  @query = @query.where(Sector: sectors_to_use) if sectors_to_use
  @query = @query.order(order_to_use) if order_to_use
  @query
end

private 

def sectors_to_use
  return [@rain_fall_type, @compare] if @search != 'All' && @compare != 'None'
  unless @rain_fall_type == 'All'
    if @rain_fall_type == 'None'
      @search == 'All' ? ['Primary', 'Secondary', 'Tertiary'] : [@search]
    else
      [@rain_fall_type]
    end  
  end
end

def order_to_use
  return nil if (@search == 'All') && (@rain_fall_type == 'All')
  return @year if (@search == 'All') && !(@year == 'All')
  return :id
end

ifs .

你可以使用一个基本上 return something if some_condition? . 这只适用于特定场景(其中一个条件是执行单个语句:

if condition?
  do_something
else
  do_something_else
end

这可以写成:

return do_something if condition?
do_something_else

这将减少代码分支。

另外,另一个建议是调用另一个具有更多条件的方法,而不是在一个快照中嵌套条件。

坏例子:

if condition?
  if condition_two?
    do_something_two
  else
    do_something
  end
else
  do_something_else
end

这可以写成:

if condition?
  call_another_method 
else
  do_something_else
end

def call_another_method
  if condition_two?
    do_something_two
  else
    do_something
  end
end

代码中的一个示例可以是:

if rain_fall_type == 'All'
  all
else
  if year == 'All'
    if rain_fall_type == "None"
      where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
    else
      # all
        where(Sector: rain_fall_type).order('id')
    end
  else
    if rain_fall_type == "All"
      order("#{year} ")

    elsif rain_fall_type == "None"
      where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id')
      else
      where(Sector: rain_fall_type).order("#{year} ")
      end
  end
end

return all if rain_fall_type == 'All'
if year == 'All'
  return where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id') if rain_fall_type == "None"
  where(Sector: rain_fall_type).order('id')
else
  return order("#{year} ") if rain_fall_type == "All"
  return where('Sector = ? OR Sector = ? OR Sector = ?', "Primary", 'Secondary', 'Tertiary').order('id') if rain_fall_type == "None"
  where(Sector: rain_fall_type).order("#{year} ")
end

我希望这能有所帮助:)

注: 这是为了回答 How to simplify big conditions? . 但最初的文章并没有遵循Rails/Ruby的搜索和过滤方式,也没有很好地利用作用域。

这可能是最好的解释,你应该如何设置这个。

class Product < ActiveRecord::Base
  # custom_scope_1
  scope :status, -> (status) { where status: status }
  # custom_scope_2
  scope :location, -> (location_id) { where location_id: location_id }
  # custom_scope_3
  scope :search, -> (name) { where("name like ?", "#{name}%")}
end

def index
   @products = Product.where(nil) # creates an anonymous scope
   @products = @products.status(params[:status]) if params[:status].present?
   @products = @products.location(params[:location]) if params[:location].present?
   @products = @products.search(params[:search]) if params[:search].present?
end

这可以进一步清理。。。

def index
  @products = Product.where(nil)
  filtering_params(params).each do |key, value|
    @products = @products.public_send(key, value) if value.present?
  end
end

private

# A list of the param names that can be used for filtering the Products
def filtering_params(params)
  params.slice(:status, :location, :search)
end

此方法使用ruby元编程来循环参数并动态调用预定义的 scopes 在模型上

您可以将此代码移动到模块中,并将其包含到任何支持筛选的模型中

app/models/concerns/filterable.rb

module Filterable
  extend ActiveSupport::Concern

  module ClassMethods
    def filter(filtering_params)
      results = self.where(nil)
      filtering_params.each do |key, value|
        results = results.public_send(key, value) if value.present?
      end
      results
    end
  end
end

app/models/product.rb

class Product
  include Filterable
  ...
end

app/controllers/product_controller.rb

def index
  @products = Product.filter(params.slice(:status, :location, :search))
end

现在,可以使用控制器中的一行和模型中的一行对模型进行过滤和搜索