How Can I Validate the Combined Length of Multiple String Properties in ASP.NET MVC?

ASP.NET MVC elegant custom validation method: combined attribute length validation

In ASP.NET MVC development, data integrity is crucial. When a model contains multiple attributes of type string, validating the combined length of those attributes can pose a challenge. This article will guide you to use the method recommended by MVC - creating custom validation properties to solve this problem.

Looking for ways to coordinate attribute lengths

Suppose your model contains four string attributes, and you need to verify that their combined length exceeds a minimum threshold. The built-in StringLength attribute only works with single property validation, so you need to find a suitable solution to combine multiple properties.

Custom validation attributes

To meet this need, ASP.NET MVC provides a powerful custom validation attribute tool. These properties allow you to define your own data validation rules, customized to the specific requirements of your application.

Use CombinedMinLengthAttribute

The key lies in the CombinedMinLengthAttribute class. Here’s how it works:

1. Receives string array and minimum length: The constructor receives an integer argument (minLength) representing the minimum combined length, and a string array (propertyNames) listing the property names to be combined.
2. Collect attribute values: In IsValid method, it extracts the value of the specified attribute and converts it into a string.
3. Calculate the total length: Determine the combined length by adding the individual string lengths.
4. Apply length check: If the total length is less than the minimum length, return a ValidationResult containing an appropriate error message.

Implemented in ViewModel

Once you have created your custom validation attribute, add it to your ViewModel:

1. Create annotated attributes: Decorate an attribute (e.g., Foo) with the CombinedMinLengthAttribute.
2. Configure annotation parameters: Specify a minimum length (e.g., 20) and provide an error message to display if validation fails.

With this custom validation, your application will effectively enforce the combined length requirements, ensuring data integrity and accuracy.

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