How to Perform Conditional Property Validation Using IValidatableObject?

Mastering Conditional Property Validation using IValidatableObject

The IValidatableObject interface is a robust tool for comprehensive object validation, especially useful for validating complex objects with inter-property dependencies. This interface allows for validations that depend on the values of other properties within the same object. However, combining this with individual property validation attributes (like [Required] or [Range]) requires careful consideration.

The IValidatableObject.Validate() method provides the mechanism to perform these conditional checks. Let's say you need to validate Prop1 and Prop2 only when the Enable property is true. Here's how you'd implement this:

<code class="language-csharp">public class ValidateMe : IValidatableObject
{
    [Required]
    public bool Enable { get; set; }

    [Range(1, 5)]
    public int Prop1 { get; set; }

    [Range(1, 5)]
    public int Prop2 { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (!Enable)
        {
            return Enumerable.Empty<ValidationResult>();
        }

        var validationResults = new List<ValidationResult>();

        // Add conditional validation rules here.  For example:
        if (Prop1 < 1 || Prop1 > 5)
        {
            validationResults.Add(new ValidationResult("Prop1 must be between 1 and 5", new[] { nameof(Prop1) }));
        }
        if (Prop2 < 1 || Prop2 > 5)
        {
            validationResults.Add(new ValidationResult("Prop2 must be between 1 and 5", new[] { nameof(Prop2) }));
        }

        return validationResults;
    }
}</code>

Crucially, when using Validator.TryValidateObject(), set the validateAllProperties parameter to false. This prevents the framework from automatically validating properties with attributes like [Range] when Enable is false, ensuring your conditional logic in Validate() takes precedence. This allows for a clean separation of concerns between individual property validation and conditional, cross-property validation.

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