### store.fetch(key, generate, callback)
Similar to read except that Thoroughfare will execute the generate function if a null value is returned from the store and store the result under key
Arguments
- key - A key of type string
- generate(key) - A function that generates the desired result for the key
- callback(err, value) - A callback which returns with the value retrieved from the store or generated if it didn't exist
Example
var generate = function(key, cb) {
return cb(null, key + "-generated");
});
store.fetch(key, generate, function(err, value) {
if (err) throw err;
console.log(value);
});