From form to collection

I know I haven't posted anything for a while. The reason for that has been a mixture of being quite busy at work and home, sheer laziness and being on leave.

I've been hacking around for the last hour trying to find the easiest/quickest way to update an array of name/date pairs within a collection from a form, and its slowing dawning on my there is no elegant or even cheeky shortcut. It would be trivial if we were representing the date as a plain string, however, I want to use the mongo ISODate; besides, there is no point in making it easy for myself.

(Before I go any further I should point out I should be doing this in the DAO not on the client. This involves pulling out the array from the JSON object and iterating over each name/date pair and using the java.util.Date to create the dates)

So, lets say I have this form with stuff on it, plus a bunch of name/date pairs that we create dynamically and populate with their current values, like this...


Now lets say I want to be able to edit the dates, and PUT the form. Rock on, we can use the code from a previous post. Convert HTML form to JSON and POST using jQuery But hold on a second, Mongo is going to expect the date as a date type. This means we need to convert it from a Date to an ISODate. Fortunately this is trivial enough.


So we need to update formToJSON to look for specific fields. Rather than fall into some Turing tarpit, I'm going to hack it so I'm solving this problem only - and then go for a swim in the tarpit later.


Now we need to make sure that mongo know is is a date type and not just a string, so we need to use $date. OK.


Well, after hacking that in, we should be about there. Well, not quite. The next hurdle is the stringify method. It will escape the double quotes and PUT the string with \" instead of ". What a pain. So after we create our JSON string we need to do a bit more "tidying up". We need to replace \" with ". We can simply use replace() right? Now of course javascript replace only replaces the first instance, so we need to be a bit cheeky and pass in the find string along with the /g modifier.


Great, we're there. Almost. Finally we need to strip the extraneous " around the date value.


Well, that was easy (-;

I'm off to factor all this into what was a relatively elegant form to json conversion.
There is an easier way to do this. However, easy is no fun.

A simple guide to finding distinct array values in a MongoDB collection

So you want to find unique values within an array within a document in a collection? A reasonable request.

In ANSI SQL you'll be using DISTINCT, JOINS and GROUP BYs, stuff you're used to, but in the NoSQL realm your best bet is mapreduce.

It might seem a little bit like hard work, and probably a little intimidating at first, but it is certainly worth it; mapreduce is an extremely powerful tool.

Set up the collection, the map and reduce functions, and execute the mapreduce command:

But now you want to find unique values within an array within each document in an entire collection.

The map function in this example iterates over each of the items and emits the key/value of each array element.

The reduce function aggregates the key/value from each of the emits from the map function. In this example we're looking at unique keys and maintaining a count of the unique keys.

If you're looking to find the distinct array elements for a single document, simply specify the document index. For the entire collection, just leave the query out. *simples*