How to Implement Conditional Property Validation Using IValidatableObject in .NET?

Conditional Validation in .NET using IValidatableObject

The IValidatableObject interface offers a powerful way to perform comprehensive object validation in .NET, including cross-property checks. However, selectively ignoring validation rules based on certain conditions can be tricky. This example demonstrates how to achieve conditional property validation effectively.

Here's a code snippet illustrating the implementation:

<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)
    {
        var results = new List<ValidationResult>();
        if (Enable)
        {
            // Conditionally validate Prop1 and Prop2
            Validator.TryValidateProperty(Prop1, new ValidationContext(this, null, null) { MemberName = "Prop1" }, results);
            Validator.TryValidateProperty(Prop2, new ValidationContext(this, null, null) { MemberName = "Prop2" }, results);

            // Add a custom conditional validation rule
            if (Prop1 > Prop2)
            {
                results.Add(new ValidationResult("Prop1 must be less than or equal to Prop2"));
            }
        }
        return results;
    }
}</code>

This code uses the Enable property to control validation. If Enable is true, it validates Prop1 and Prop2 using the [Range] attribute and a custom rule ensuring Prop1 is not greater than Prop2. The Validator.TryValidateProperty() method is key; it only adds validation errors to the results list if validation fails.

To utilize this validation:

<code class="language-csharp">public void PerformValidation()
{
    var toValidate = new ValidateMe
    {
        Enable = true,
        Prop1 = 6,  //This will cause a validation error
        Prop2 = 2
    };

    bool validateAllProperties = false; // Important: Set to false for conditional validation

    var results = new List<ValidationResult>();
    bool isValid = Validator.TryValidateObject(toValidate, new ValidationContext(toValidate, null, null), results, validateAllProperties);

    //Process validation results (results list)
}</code>

Setting validateAllProperties to false is crucial. This prevents Validator.TryValidateObject() from overriding the conditional validation logic. This approach combines IValidatableObject with conditional validation for flexible and robust object validation in your .NET applications.

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