How to arrange into datatables using JSON

take this example: http://pastebin.com/U2ZQ4m3Y

I want to arrange the above json code into columns of datatables,I am unable to do it. I have tried using

"ajax": "json.txt"
columns : [
{mdata:campaign_name},
{mdata:campaign_id},
{mdata:campaign_desc}
]

but mdata is unable to read the nested data source ,Can you suggest me how I may be able to arrange them into columns..