How do I add custom validation to a Razor page?

Question

I'm working with MVC 4 for the first time. I have business logic that is a little complex but I would imagine not that uncommon. I have items that can be resized within a specific range. The range depends upon the item. ``` public class MyItem { public double Width { get; set; } public double MinWidth { get; set; } public double MaxWidth { get; set; } } ``` `CustomWidth` when set by a user has to be within `MinWidth` and `MaxWidth` inclusively. This seems like a common problem. I've tried the `CustomValidation` attribute but it only validates when I try to save the entity to my database (using Entity Framework). This is the Razor page I'm working with. ``` @using (Html.BeginForm("Action", "Controller", FormMethod.Post)) {

Accepted Answer

To do custom validation, you want to inherit from `IValidatableObject`.

**Note custom validation will happen after initial model validation is successful

```
    public class MyItem : IValidatableObject
        {
            public double Width { get; set; }

public double MinWidth { get; set; }

public double MaxWidth { get; set; }
            public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
           {
                // Custom validation
           }

}
```

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How do I add custom validation to a Razor page?

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