Can I add extra data to an oraclize query so that I can use it in the callback function?

Question

I would like to be able to use certain data in the callback of an oraclize query that I want to pass in when creating the oraclize query.

Say I have the following function in a contract:

function updateExchangeRate(uint delay, uint userId){
    oraclize_query(delay, "URL", "json(https://min-api.cryptocompare.com/data/price?fsym=ETH&tsyms=USD).USD");
    // have the userId value be usable in the oraclize callback function
  }

Is it possible to add data to that query than can be used in the callback function? I want to pass in a userId every time I make an oraclize query that I can then use in the callback function.

Is that possible?

Answer 1

Use the query ID that comes back from the request and then store that as a mapping with the user ID. Here is the section in the docs (the link in the comments isn't working): http://docs.oraclize.it/#ethereum-quick-start-the-query-id.

bytes32 queryId = oraclize_query(60, "URL", "json(http://api.fixer.io/latest?symbols=USD,GBP).rates.GBP");