An asp.net-mvc plugin to provide client and server side validation for collection properties of a model.

The project consists of 3 components:

• Validation Attributes that are applied to collection properties which provide server side validation
• A HtmlHelper extension method to generate a placeholder in the view for client and server side error messages
• A jQuery plugin that provides client side validation

The validation attributes include (so far)

Asserts that at least one object in the collection must have a specified property set to a specified value.

For example, a UserViewModel might have a List<RoleViewModel> property, where RoleViewModel contains a bool IsSelected property that is rendered as a checkbox in the view. To assert that at least one Role is selected, the attribute would be applied as

[RequireInCollection("IsSelected", true)]
public List<RoleViewModel> Roles { get; set; }

The attribute also includes Minumum and Maximum properties to assert that, for example, a minumun of 3 Roles must be selected, or between 2 and 4 Roles must be selected.

Asserts that for each object in a collection, that the value of a specified property must have a unique value.

For example, a SurveyViewModel might have a List<ProductViewModel> property, where ProductViewModel contains a int Rating property that is rendered in the view as a numeric textbox (and is used to rate each product in order of preference). To assert that the value of each Rating is unique, the attribute would be applied as

[UniqueInCollection("Rating")]
public List<ProductViewModel> Products { get; set; }

Asserts that the total of a specified property of the object in the collection must be within a specified range.

The @Html.CollectionValidationMessageFor() extension method is used to generate the placeholder element in the view to display the error message if the the collection property is invalid (the equivalent if @Html.ValidationMessageFor()).

The default element is <span>.

The sandtrap-collection-validation.js plugin is responsible for client side validation.

Client side validation is 'lazy'. It is not triggered until the form is first submitted. If the data is not valid, the submit is cancelled and error messages are displayed. Thereafter, validation is triggered on the .change() event of the appropriate form controls so that error messages are removed as soon as the data is valid.