Javascript Form Validation

This is an incredibly common problem, and there’s really no reason to reinvent the wheel. That said, yesterday I thought of (what I think is) a rather neat way of solving the problem. So I’ve deliberately not looked in-depth at how others have solved this particular problem, and instead made a quick sketch of my solution. When I do look, I think I’ll be looking at the jQuery Validation Plugin.

In short, this model is inspired by jQuery’s ability to chain queries together, to give succinct, powerful syntax. There are two essential things that I want to be able to do:

1. Check if a condition is present
2. Assert that something should be so

My aim is to be able to do this with code that looks like this:

vl.ifEqual("detailrequired","Full")
  .assertNotEmpty("If full details are required,"
                  + "contributions must be entered",
                  "contributions");

But let’s start at the beginning. Form validation: there are many levels. Let me enumerate some:

1. Required fields
2. Fields having the correct format
3. Inter-field validation (eg a start date falling before an end date)

In this sketch, I’m particularly thinking of the third level of form validation. In the example of a start and end date, all I want to do is check that the start date falls before the end date, and it it does, throw an error. I can do that with this code (error handling removed for brevity):

var startdate = Date.parse(document.getElementById("startdate").value);
var enddate = Date.parse(document.getElementById("enddate").value);
if (startdate > enddate) {
    alert("Start date must fall before the end date");
}

Simple enough, but rather wordy – particularly when you get in to handling errors and unexpected input. A more complex example might be to check the value of one field, and depending on its value, apply a particular rule. For example, if a field detailsrequired equals full, then a number of other fields are required. This could be achieved with this Javascript:

if (document.getElementById("detailsrequired").value=="Full") {
    if (document.getElementById("contribututions").value=="") {
        alert("If full details are required, "
               + "contributions must be entered");
    }
}

These individual samples aren’t very complex, but once you add code to handle exceptions, then they blow out a little bit. It’s also quite verbose. To achieve the syntax outlined above, where I can chain the checks and assertions together, I need to create an object that returns a reference to itself when you call any of its methods – the same way as jQuery works.

In the following code excerpt, I create two functions, and then bind them to a function object, ValidationLibrary. First a word on the function object: it has a single property, ‘check’, that is set by its single parameter. This parameter is used by the function assertEmpty. If this.check is true, then it will apply the assertion. If not, it doesn’t do anything.

The ifEqual function takes two parameters and compares them. If they are equal, it returns the parent object unaltered. On the other hand, if it they are unequal, it returns a new ValidationLibrary with check set to false – thus disabling any subsequent assertions.

function ifEqual(a, b) {
    if (a!=b) {
        return new ValidationLibrary(false);
    }
    return this;
}

function assertNotEmpty(msg, a) {
    if (this.check) {
        if (a=="") {
            this.error(msg);
        }
    }
    return this;
}

function ValidationLibrary(check) {
     this.check = check;
     this.assertNotEmpty = assertNotEmpty;
     this.ifEqual = ifEqual;
} 

With this framework, the example above becomes:

var vl = new ValidationLibrary(true);
vl.ifEqual(f("detailsrequired"),"Full")
  .assertNotEmpty("If full details only are required, "
                    + " contribution must be provided",
                  f("contribution"));

Note: I’ve created a function f(id) that returns the value of a form field, given a particular ID. If the form field contains a date, a Date object will be returned. If the form field contains a number, a Number object will be returned. Otherwise, a string will be returned.

With this framework, there’s a lot less boilerplate in order to get the same effect, and behind the scenes there is (or is in theory) a lot more error checking.

As above, this is only a rough sketch to capture the idea. I’m still to go and look at how other people have solved this same problem. And to be usable, a lot more would need to be done on this framework: the way assertions are reported in particular would need a lot of work, and even a cursory glance shows the the jQuery Validation plugin does a much better job of simple validations like making a field mandatory.

That said, the main idea I wanted to jot down was a way of handling more complex validations in an elegant way: I’m curious to see what other options are already in use.

In the meantime, please feel free to check out the rough demo and peruse the full javascript files, ValidateLibrary.js and FormValidations.js.

Installing Oracle Instant Client (and connecting to Oracle from Excel)

‘Instant’ probably overstates it somewhat, but the Oracle Instant Client does let you connect to an Oracle database in a reasonably snappy way. It’s pretty straight-forward too, but there are a few hoops to jump through. Here’s how I got it working.

Installing Instant Client

1. Download the Instant Client. You’ll need the ‘basic’ or ‘basiclite’ packages, and you’ll probably want one of the add-ons, like the jdbc driver (for Java) or the odbc driver. I grabbed the odbc driver, because I’m going to connect via Excel. You’ll need to sign up to the Oracle website to access the downloads. I’ve been a member for a while, and it seems pretty harmless – no spam that I’ve noticed. Once you’ve downloaded the packages, unzip them to the same directory.
2. The current packages ship without some necessary DLLs, as detail on the OTN Discussion Forum. The missing DLLs are MFC71.dll, msvcr71.dll and MFC71ENU.dll. I believe they’re part of the Visual Studio install, and I had them on my PC, but I needed to drag them into the install directory. If you don’t have them, you can google them (if you’re feeling lucky.) Update: looks like they’ve updated the packages, and you shouldn’t need to track down these dlls any longer.
3. Place this directory where you want it and run odbc_install.exe. The install adds some registry settings to register to odbc driver, and it points to the driver in the directory you’re using.
4. Create an environment variable called TNS_ADMIN. The value should be the path to the directory that contains tnsnames.ora, which lets the Oracle driver know what servers are available. Managing tnsnames.ora can be frustrating, especially for the uninitiated (that is, me), and in a subsequent post, I’ll detail how to connect without tnsnames.ora.
5. You’ll also need to create an NLS_LANG environmental value. Oracle recommends you set this in the registry, but the instantclient doesn’t create the registry structures needed. You could create them, but it’s easier to create the environmental variable. Oracle provides a list of possible values.
6. You can now connect to your Oracle DB using Microsoft Query.

Update: The promised post to connect using VBA is on it’s way! In the meantime, to connect with Microsoft Query, there’s a few things to be aware of.

Connecting with Microsoft Query

Firstly, your TNS_ADMIN environment variable must point to a valid file – or this won’t work. If you’re connecting to Oracle Express Edition, then you’re tnsnames.ora will look like this:

XE =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = XE)
)
)

If you’re connecting to another Oracle database, you’ll need to find the appropriate tnsnames.ora. It might be under a path like C:/oracle/network/admin/. Without TNS_ADMIN pointing to a directory with a valid tnsnames.ora, you won’t be able to connect using this method.

There are two ways of setting up the connection. The first is directly through Microsoft Excel. The second is through ODBC Data Source Administrator. ODBC Data Source Administrator is probably the better way, but I’ll look at setting it up through Excel first.

New connection through excel

1. In Excel, start Microsoft Query. In Office 2007, go to the Data ribbon and click on Get External Data -> From Other Sources -> Microsoft Query.
   
2. Leave <New Data Source> selected and click OK. The Create New Data Source dialogue will be displayed. Enter a name for the data source, and the driver drop-down becomes enabled. Select Oracle in instantclient_11_2 (or similar).
   
3. Click connect. The service name must much a valid service name in the tnsnames.ora. If you’re using the Oracle Express example above (and have installed the Oracle Express client with default settings) this will be XE. The username and password will be whatever you or the sysadmin set.
   
4. Click OK. If you cannot connect at this point, but you can connect to the database by other means, it most likely means that your tnsnames.ora is wrong or that TNS_ADMIN is not pointing to the right directory (note that if you change the environmental variable, you’ll need to restart Excel for the change to take effect.)
5. All being well, you will now be able to select a default table (if you choose to) and use Microsoft Query as you normally would.
   

Congratulations! You’re now connected to Oracle using Microsoft Query!

Creating the connection in ODBC Data Source Administrator

It’s often easier and more convenient to set up the new data source through the ODBC Data Source Administrator. This way, the new data source will be available whenever you want to use it, rather than needing to recreate it every time.

1. Open the ODBC Data Source Administrator. This is in Control Panels. Under Windows 7 64bit you’ll need to choose the appropriate version: odbcad32.exe under either system32 or SysWOW64, depending on whether you’re setting up a connection for 32bit or 64 bit applications.
   
2. Click Add. The Create New Data Source window appears. Choose the Oracle in instantclient_11_2 driver and click OK.
   
3. The Oracle ODBC Driver Configuration page will open. This page gives you far more options and is more intelligent than the equivalent if you create the connection in Excel. The TNS Service Names drop-down box will populate with the databases specified in tnsnames.ora: if no options appear, then either your tnsnames.ora file is invalid, or TNS_ADMIN is not specified correctly. Again, if you change TNS_ADMIN, you’ll need to restart ODBC Data Source Administrator for the change to take effect.
   
4. Click ‘Test Connection’. You’ll be prompted to enter a password, and all being well, you’ll get this dialogue:
   
5. Click OK in the Data Source Configuration dialogue, and open Microsoft Excel. The new Data Source will appear when you open Microsoft Query.
   
6. Click OK and you can use the connection in Microsoft Query as usual.

Still to come…

So that’s two different ways to connect to Oracle in Excel using Microsoft Query. As soon as I have time, I’ll be posting a sample workbook and instructions on how to connect to Oracle using VBA instead of Microsoft Query, which is especially handy if you want to distribute the workbook.