How can I make it DRY?

Question

if condition1
   ModelName.named_scope1(parameter).named_scope2.named_scope3(parameter).named_scope4
elsif condition2
   ModelName.named_scope1(parameter).named_scope2.named_scope3(parameter).named_scope5
elsif condition3
   ModelName.named_scope1(parameter).named_scope2.named_scope3(parameter).named_scope6
elsif 
   ModelName.named_scope1(parameter).named_scope2.named_scope3(parameter).named_scope7
end  

To solve the above issue I have written it something like this but it fires two queries.

values = ModelName.named_scope1(parameter).named_scope2.named_scope3(parameter)

if condition1
   values.named_scope4
elsif condition2
   values.named_scope5
elsif condition3
   values.named_scope6
elsif 
   values.named_scope7
end  

Any solution ?

Answer 1

Your first and second examples do exactly the same thing, so the original implementation must have also been sending two queries. I think your pseudo-code is a little too generic to comment further, but generally when I have lists of if..elsif..else conditions (or long case..when's for that matter), I try to consider if I could use a lookup table (just a Hash) instead. It may not directly apply to your example, however.

So instead of something like this:

case value
  when "one"
    obj.do_something(1, 2, 3)
  when "two"
    obj.do_something(4, 5, 6)
  when "three"
    ...
end

Re-think it as:

args_map = {
  "one"   => [1, 2, 3],
  "two"   => [4, 5, 6],
  "three" => ...
}

obj.do_something(*args_map[value])

Answer 2

您可以构建动态范围，尽管在不确切知道如何确定范围选择标准的情况下，很难说出动态范围代码可能在哪里 ，或者明显的解决方案（您自己）是否更清楚。