instance variables don't seem to be populated in ruby method chaining

Question

I have a class I'm using build complex objects via method chaining. I'm new to ruby so I must be missing something obvious here. I expect a hash to be returned that looks like this: {"must"=>[{:match=>{"status_type" : "good"}}, {:match=>{"product_age" : "old"}}]}

But all I get is this: {"must"=>[{:match=>{}}]}

I invoke the following code for the above attempts:

builder = QueryBuilder.new
built = builder.must("status_type").equals("good").must("product_age").equals("old")
built.serialize_this

Here is my class. I'd appreciate any help as I'm pretty new to Ruby.

class QueryBuilder
    attr_accessor :query_hash, :context, :condition_hash

    def initialize
        @query_hash = {}
        @condition_hash = {}
    end

    def serialize_this
        return @query_hash
    end

    def must(search_field)
        @context = "must"
        @condition_hash[search_field] = "temp"
        return self
    end

    def should(search_field)
        @context = "should"
        @condition_hash[search_field] = "temp"
        return self
    end

    def equals(value_field)
        search_field = @condition_hash.keys[0].to_s
        @condition_hash[search_field] = value_field
        match_hash = {}
        match_hash[:match] = @condition_hash
        an_array =[]
        an_array << match_hash
        @query_hash[@context] = an_array
        @condition_hash.clear
    return self
    end
end

Thanks a ton in advance for any light you can shed on my code.

It is more idiomatic to not explicitly return something at the end of methods. For e.g., in the last line of the `equals` method, just write `self` instead of `return self`. — yihangho, Jul 22 '15 at 00:07
It shouldn't. I was saying that it's more idiomatic, not it will solve the problem. — yihangho, Jul 22 '15 at 00:09
That's true it is more idiomatic from what I've read. But return makes it easier to read. Some ruby industry experts are actually proponents to using return explicitly from what i have heard — Horse Voice, Jul 22 '15 at 00:11
True that certain people think it's easier to read. Just thought you should know since you mentioned you're new to Ruby. — yihangho, Jul 22 '15 at 00:12

score 1 · Accepted Answer · edited May 23 '17 at 12:06

1

When you do this:

match_hash[:match] = @condition_hash

You don't put a copy of a Hash there, you put a reference to a hash. It's the very same hash that you clear later.

Is Ruby pass by reference or by value?

edited May 23 '17 at 12:06

Community

1
1

answered Jul 22 '15 at 00:18

wired9

44
1

great! that does fix the empty hash problem, but it missed out of status_type => good. It only shows the second hash which is: `{"must"=>[{:match=>{"product_age"=>"old"}}]}` – Horse Voice Jul 22 '15 at 00:53
Of course, you instantiate a new array each time and put a value to it. The old array is lost. – wired9 Jul 22 '15 at 01:04
got it. I see we have to do this: `(@query_hash[@context] ||= []) << match_hash ` – Horse Voice Jul 22 '15 at 01:19

instance variables don't seem to be populated in ruby method chaining

1 Answers1