轨道总和活动记录关联关系

Question

I have Foo::ActiveRecord_AssociationRelation and I when I run this code in the console on that relation:

.inject(0){|sum,x| x.dimension == dimension && x.dimension_value == dimension_value && x.metric == metric ? (sum += x.metric_value) : ()}

I get the expected summed value it should return.

However when I added this code to the model

def self.sum_by(dimension, dimension_value, metric)
...
end

I get this error:

NoMethodError: undefined method `inject' for #<Class:0x000000094cbbd0>

How do I apply that code correctly? Given that Foo inherits from ActiveRecord::Base I thought it should work.

Answer 1

I'm assuming that you are removing the leading period when you copy it into a class.

However, inject is not a method on an ActiveRecord::Base object. It is from the Enumerable module, so you'd need to call it on something that has the enumerable module mixed in.

For instance, if you were trying to sum every instance of Foo, you could call Foo.all first, returning an array of all objects. so your code would look as follows.

def self.sum_by(dimension, dimension_value, metric)
  Foo.all.inject(0){|sum, a_foo| foo.dimension == dimension && foo.dimension_value == dimension_value && foo.metric == metric ? (sum += foo.metric_value) : ()}
end