Question

Beginning rails programmer here. I’m trying to convert a hash to both xml and json, but the output is different.

Here’s the hash:

{:exchangeRates=>[{:baseCurrency=>"USD", :quoteCurrency=>"EUR", :amount=>1, :nprices=>1, :conversions=>[{:date=>Tue, 20 Nov 2012 21:00:00 +0000, :ask=>"0.7813", :bid=>"0.7813"}]}, {:baseCurrency=>"CAD", :quoteCurrency=>"EUR", :amount=>1, :nprices=>1, :conversions=>[{:date=>Tue, 20 Nov 2012 21:00:00 +0000, :ask=>"0.7839", :bid=>"0.7837"}]}]}

Here’s the corresponding render code

format.json { render :json => { :response => rates.to_hash() } }

and here’s the JSON (which is what I want)

{"response": {"exchangeRates": [
    {
        "baseCurrency": "USD",
        "quoteCurrency": "EUR",
        "amount": 1,
        "nprices": 1,
        "conversions": [{
            "date": "2012-11-20T21:00:00+00:00",
            "ask": "0.7813",
            "bid": "0.7813"
        }]
    },
    {
        "baseCurrency": "CAD",
        "quoteCurrency": "EUR",
        "amount": 1,
        "nprices": 1,
        "conversions": [{
            "date": "2012-11-20T21:00:00+00:00",
            "ask": "0.7839",
            "bid": "0.7837"
        }]
    }
]}}

Here’s my xml render code:

format.xml { render :xml => rates.to_hash(), :root => 'response' }

Here’s the xml output (there are extra tags where I put in arrays):

<response>
    <exchangeRates type="array">
        <exchangeRate>
            <baseCurrency>USD</baseCurrency>
            <quoteCurrency>EUR</quoteCurrency>
            <amount type="integer">1</amount>
            <nprices type="integer">1</nprices>
            <conversions type="array">
                <conversion>
                    <date type="datetime">2012-11-20T21:00:00+00:00</date>
                    <ask>0.7813</ask>
                    <bid>0.7813</bid>
                </conversion>
            </conversions>
        </exchangeRate>
        <exchangeRate>
            <baseCurrency>CAD</baseCurrency>
            <quoteCurrency>EUR</quoteCurrency>
            <amount type="integer">1</amount>
            <nprices type="integer">1</nprices>
            <conversions type="array">
                <conversion>
                    <date type="datetime">2012-11-20T21:00:00+00:00</date>
                    <ask>0.7839</ask>
                    <bid>0.7837</bid>
                </conversion>
            </conversions>
        </exchangeRate>
    </exchangeRates>
</response>

As you can see, it is adding the extra “array” attribute tags, i.e. exchangeRates and conversions. How do I get this to format the same as the json? I also don’t want the attributes on any of the tags either. I know you can pass in attributes, such as :root => ‘response’, but after looking for quite some time, I can’t seem to find a listing of these attributes on the web.

Any help would be greatly appreciated, thanks!

Answer 1

This is a case where it’s best just to go directly to the source code. The to_xml method is in the ActiveModel::Serializer module, here are the inline docs, which don’t mention anything about the type="array" attribute tags. Dig a bit deeper though and you’ll see they appear in the same file on line 130 of a method called add_associations.

rails/activemodel/lib/active_model/serializers/xml.rb:130

type = options[:skip_types] ? { } : {:type => "array"}

That tells us that there’s an option called skip_types, which appears to be documented nowhere. Try passing that to to_xml, and you get the desired behaviour:

a = [1, 2, 3]
a.to_xml
#=> "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<fixnums type=\"array\">\n  <fixnum type=\"integer\">1</fixnum>\n  <fixnum type=\"integer\">2</fixnum>\n  <fixnum type=\"integer\">3</fixnum>\n</fixnums>\n"
a.to_xml(:skip_types => true)
#=> "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<fixnums>\n  <fixnum>1</fixnum>\n  <fixnum>2</fixnum>\n  <fixnum>3</fixnum>\n</fixnums>\n"

You’ll notice all the added type attributes are gone.

So just pass the same option to render and you’ll get the desired result:

format.xml { render :xml => rates.to_hash(), :root => 'response', :skip_types => true }