Скачать или смотреть How to Cleanly Share a Custom Validator Across Data Models in ASP.NET

Discover a simple and effective approach to `share custom validation attributes` across your DTOs, ViewModels, and Data Models in ASP.NET MVC with this detailed guide.
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This video is based on the question https://stackoverflow.com/q/65609729/ asked by the user 'Phil G' ( https://stackoverflow.com/u/9160880/ ) and on the answer https://stackoverflow.com/a/65609899/ provided by the user 'user1672994' ( https://stackoverflow.com/u/1672994/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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A Clean Approach to Sharing Custom Validators in ASP.NET

In the world of ASP.NET MVC, maintaining clean and efficient code can often be a challenge, especially when it comes to validating data across different layers of your application. One of the common hurdles developers face is how to share a custom validation attribute, such as a ValidationAttribute, across various models—specifically between a Data Model, a ViewModel, and a Data Transfer Object (DTO). This guide aims to provide not only a solution to this problem but also an explanation of how you can implement it in a more elegant way.

The Problem

Imagine you are developing a REST Web API using ASP.NET WebAPI 2, while also implementing MVC 5 views. You have created a custom validation attribute, Min18YearsIfAMember, to validate the age of users based on their membership type. This attribute is used on a date of birth field across various models, such as your Customer data model and CustomerDto. However, your current implementation requires you to cast ValidationContext.ObjectInstance to each specific type—resulting in cluttered and less readable code.

Example of the Current Approach

The existing code snippet you might be using could look something like this:

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As you can see, the code checks each type individually, which can become tedious and difficult to maintain.

The Solution

Instead of checking each object type, you can enhance your Min18YearsIfAMember attribute by introducing a dependent property. This allows your validator to seamlessly get the necessary property values without extensive type checking. Here’s how you can implement this solution:

Step 1: Modify the Custom Attribute

You’ll need to modify your custom validation attribute to accept a string parameter representing the name of the dependent property. Here's how your modified attribute will look:

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Step 2: Apply the Attribute in Your Models

Now, when applying this validation attribute to your properties, you specify the dependent property's name. Here’s an example of how to do this in your Customer model:

[[See Video to Reveal this Text or Code Snippet]]

By using nameof(MembershipTypeId) when applying the attribute, you eliminate the hard-coding of strings and improve the maintainability of your code.

Conclusion

Using the improved method of sharing a custom validator in ASP.NET MVC, you're not only keeping your code base cleaner and more elegant but also enhancing its readability and maintainability. This approach allows for the elimination of repetitive type checking while still ensuring that your validation logic remains robust and effective. Give it a try in your projects, and see how it streamlines your validation processes!