Testing reusable validation

In the application we are developing, a lot of input validation takes place. Most of the input is validated using Command Objects, which are a breeze to use thanks to Grails’ fantastic way of integrating them. However, in some of our Command Objects, there’s some overlap, most notably in the validation part. For example, we use a CreateCustomerCommand and a OrderProductCommand, which both have a ‘zipcode’ field, which, in our case, matches the regular expression [0-9]{4}[a-zA-Z]{2}. Since we don’t want to duplicate this regular expression, we need to come up with a solution to be able to reuse this.

One way of accomplishing this is to use Grails Global Constraints. Grails Global Constraints allow you to define your Constraints once, and reuse them in your application. However, (IMO) there are some downsides to this technique. One of them is testing these validations. I still haven’t found a way to Unit test these validations, even though I spent quite some time looking into a way to accomplish this. Another downside is that these validations are in the Config.groovy, which pollutes your configuration with application logic. Not the best way to accomplish this.

The alternative way, which is the way we are using, is to create something simple ourselves. We created a SharedConstraints class, which contains all the shared validations in our application. A small example:

To use this, do the following:

The only thing left is testing this. To test the simcard number validation in isolation, we use the following code:

Creating this simple infrastructure class enables you to easily test constraints, which can be reused in all commands or domain objects.

6 replies
    • Erik Pragt
      Erik Pragt says:

      Hi Hubert, thanks for the reply. I wasn’t aware of this plugin, but I’ll check it out and see how it compares to our current method. Thanks for the tip!

      • Zoran F.
        Zoran F. says:

        Hi Erik!
        Thank you for this cool approach. I tried your approach, but having a problem when I want do have more than one custom constraint on a field:
        static constraints = {
        name(SharedConstraints.checkA, SharedConstraints.checkB)

        As I’m pretty new to grails I don’t if this is possible?

        Anyway, do you still use this approach or you switched to contraints plugin?

        Thank you very much!

  1. Ryan V
    Ryan V says:

    Zoran F., I’m pretty sure there is a grails limitation in 1.x that you can only have 1 custom constraint per field. If you need multiple, you have to make a new custom constraint that encompasses the others. I know, annoying. Not sure if 2.0 addresses this or not.

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