Validation in Breeze and Knockout

Question

I've recently added Breeze to a project using Knockout and ASP.NET MVC4. I really like Breeze and it saves a lot of coding.

I have used Knockout validation and like how it validates a property field text box on data entry and the way the error message is displayed.

I would like to use a combination where the validation requirements are defined in the back-end with C# attributes on the object properties, the validation requirements are received in the metadata and then Knockout validation can be used.

I think I can work around it by defining the properties in the front end and applying Knockout validation eg

classProperty.extend({ required: true })
             .extend({ minLength: 3 });

Is there a way to use Knockout validation without having to apply the validation requirements in the front-end? If not, are you considering doing this?

This question was posted by johnvarney on our IdeaBlade forums. I am reposting the question and answer here since I think it will be useful to the Breeze Stack Overflow community.

Answer 1

As you've probably noticed, Breeze already performs validations based on metadata. Basic "validation" rules such as whether a property is required, it's datatype and it's length if a string are automatically generated on the server and sent down to the client. These validation rules can also be extended by directly modifying the "validation" metadata on the client.

More information on this topic is available both within the API documentation: http://www.breezejs.com/sites/all/apidocs/classes/Validator.html as well as within the "DocCode" sample directory in the Breeze Samples download.

We are also planning on providing examples of how to "connect" breeze validation to various third party libraries, such as jQuery and Knockout. Unfortunately, these examples are not currently a high priority because of work on other highly requested features. You might want to vote for work on these examples on our Breeze User Voice https://breezejs.uservoice.com/forums/173093-breeze-feature-suggestions. We take that venue seriously in making decisions about what to do next.