Inject with embedded conditional...possible?

Question

I'm expecting 9, but getting nil. Not sure why.

> dfs = p.disk_items.inject { |acc, di| acc + 1 if di.type == "DiskFile" }
=> nil

The same problem:

> dfs = p.disk_items.inject(0) { |acc, di| if di.type == "DiskFile" then acc + 1 end } 
=> nil

Clearly there are nine occurrences where di.type == "DiskFile" is true:

> dfs = p.disk_items.inject(0) { |acc, di| puts di.type == "DiskFile" }
true
true
true
true
true
true
true
true
true
false
=> nil

What am I screwing up? If I can't use conditionals, then maybe there's a better way to count all the ActiveRecord objects in an array that satisfies a condition on an attribute.

Edit: FWIW:

> p.disk_items.class
=> ActiveRecord::Associations::CollectionProxy::ActiveRecord_Associations_CollectionProxy_DiskItem

looks like this implementation in Rails source of count may not accept blocks? Though I may be reading this wrong or looking in the wrong place...

Answer 1

user2246674 is correct, the if statement is returning nil, but inject should always return acc You can use a turnery operator to make this easy

dfs = p.disk_items.inject(0) { |acc, di| di.type == "DiskFile" ? acc + 1 : acc  }

Answer 2

When the if "doesn't run" the block evalutates to nil. This happens on the last case and the result (nil) is returned.

Consider (the long-hand):

if di.type == "DiskFile" then
    acc + 1
else
    acc      # so we never return nil
end

While there are various short-hands (i.e. ?:), I would use a count {block}. If needing to do something else with the values (perhaps still using in an inject "sometimes"), select might also be useful.

p.disk_items.count {|di| di.type == "DiskFile"}