DataAnnotations: Recursively validating an entire object graph

I have an object graph sprinkled with DataAnnotation attributes, where some properties of objects are classes which themselves have validation attributes, and so on.

In the following scenario:

public class Employee
{
    [Required]
    public string Name { get; set; }

    [Required]
    public Address Address { get; set; }
}

public class Address
{
    [Required]
    public string Line1 { get; set; }

    public string Line2 { get; set; }

    [Required]
    public string Town { get; set; }

    [Required]
    public string PostalCode { get; set; }
}

If I try to validate an Employee's Address with no value for PostalCode, then I would like (and expect) an exception, but I get none. Here's how I'm doing it:

var employee = new Employee
{
    Name = "Neil Barnwell",
    Address = new Address
    {
        Line1 = "My Road",
        Town = "My Town",
        PostalCode = "" // <- INVALID!
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};

Validator.ValidateObject(employee, new ValidationContext(employee, null, null));

What other options do I have with Validator that would ensure all properties are validated recursively?

Here's an alternative to the opt-in attribute approach. I believe this will traverse the object-graph properly and validate everything.

public bool TryValidateObjectRecursive<T>(T obj, List<ValidationResult> results) {

bool result = TryValidateObject(obj, results);

var properties = obj.GetType().GetProperties().Where(prop => prop.CanRead 
    && !prop.GetCustomAttributes(typeof(SkipRecursiveValidation), false).Any() 
    && prop.GetIndexParameters().Length == 0).ToList();

foreach (var property in properties)
{
    if (property.PropertyType == typeof(string) || property.PropertyType.IsValueType) continue;

    var value = obj.GetPropertyValue(property.Name);

    if (value == null) continue;

    var asEnumerable = value as IEnumerable;
    if (asEnumerable != null)
    {
        foreach (var enumObj in asEnumerable)
        {
            var nestedResults = new List<ValidationResult>();
            if (!TryValidateObjectRecursive(enumObj, nestedResults))
            {
                result = false;
                foreach (var validationResult in nestedResults)
                {
                    PropertyInfo property1 = property;
                    results.Add(new ValidationResult(validationResult.ErrorMessage, validationResult.MemberNames.Select(x => property1.Name + '.' + x)));
                }
            };
        }
    }
    else
    {
        var nestedResults = new List<ValidationResult>();
        if (!TryValidateObjectRecursive(value, nestedResults))
        {
            result = false;
            foreach (var validationResult in nestedResults)
            {
                PropertyInfo property1 = property;
                results.Add(new ValidationResult(validationResult.ErrorMessage, validationResult.MemberNames.Select(x => property1.Name + '.' + x)));
            }
        }
    }
}

return result;
}

Most up-to-date code: https://github.com/reustmd/DataAnnotationsValidatorRecursive

Package: https://www.nuget.org/packages/DataAnnotationsValidator/

Also, I have updated this solution to handle cyclical object graphs. Thanks for the feedback.

You can extend the default validation behavior, making the class you want to validate implement the IValidatableObject interface

public class Employee : IValidatableObject
{
    [Required]
    public string Name { get; set; }

    [Required]
    public Address Address { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        var results = new List<ValidationResult>();

        Validator.TryValidateObject(Address, new ValidationContext(Address), results, validateAllProperties: true);

        return results;
    }
}

public class Address
{
    [Required]
    public string Line1 { get; set; }

    public string Line2 { get; set; }

    [Required]
    public string Town { get; set; }

    [Required]
    public string PostalCode { get; set; }
}

And validate it using the Validator class in one of these ways

Validator.ValidateObject(employee, new ValidationContext(employee), validateAllProperties: true);

or

var validationResults = new List<ValidationResult>();
Validator.TryValidateObject(employee, new ValidationContext(employee), validationResults, validateAllProperties: true);

I found this issue while searching for a similar problem I had with Blazor. Seeing as Blazor is becoming increasingly more popular I figured this would be a good place to mention how I solved this problem.

Firstly, install the following package using your package manager console: Install-Package Microsoft.AspNetCore.Components.DataAnnotations.Validation -Version 3.2.0-rc1.20223.4

Alternatively you can also add it manually in your .csproj file:

<ItemGroup>
<PackageReference Include="Microsoft.AspNetCore.Components.DataAnnotations.Validation" Version="3.2.0-rc1.20223.4" />
</ItemGroup>

Having added and installed this package one can simply add the following data annotation to any object to indicate that it is a complex type. Using the example OP provided:

public class Employee
{
    [Required]
    public string Name { get; set; }

    [ValidateComplexType]
    public Address Address { get; set; }
}

public class Address
{
    [Required]
    public string Line1 { get; set; }

    public string Line2 { get; set; }

    [Required]
    public string Town { get; set; }

    [Required]
    public string PostalCode { get; set; }
}

Take note of the [ValidateComplexType] annotation above the Address reference.

For the ones that also found this post when using Blazor: make sure your EditForm uses this AnnotationValidator instead of the normal one:

<ObjectGraphDataAnnotationsValidator />

Source: https://learn.microsoft.com/en-us/aspnet/core/blazor/forms-validation?view=aspnetcore-3.1#blazor-data-annotations-validation-package

Code:

public class DataAnnotationsValidator : IDataAnnotationsValidator
{
    public bool TryValidateObject(object obj, ICollection<ValidationResult> results, IDictionary<object, object> validationContextItems = null)
    {
        return Validator.TryValidateObject(obj, new ValidationContext(obj, null, validationContextItems), results, true);
    }

    public bool TryValidateObjectRecursive<T>(T obj, List<ValidationResult> results, IDictionary<object, object> validationContextItems = null)
    {
        return TryValidateObjectRecursive(obj, results, new HashSet<object>(), validationContextItems);
    }

    private bool TryValidateObjectRecursive<T>(T obj, List<ValidationResult> results, ISet<object> validatedObjects, IDictionary<object, object> validationContextItems = null)
    {
        //short-circuit to avoid infinite loops on cyclic object graphs
        if (validatedObjects.Contains(obj))
        {
            return true;
        }

        validatedObjects.Add(obj);
        bool result = TryValidateObject(obj, results, validationContextItems);

        var properties = obj.GetType().GetProperties().Where(prop => prop.CanRead
            && !prop.GetCustomAttributes(typeof(SkipRecursiveValidation), false).Any()
            && prop.GetIndexParameters().Length == 0).ToList();

        foreach (var property in properties)
        {
            if (property.PropertyType == typeof(string) || property.PropertyType.IsValueType) continue;

            var value = obj.GetPropertyValue(property.Name);

            if (value == null) continue;

            var asEnumerable = value as IEnumerable;
            if (asEnumerable != null)
            {
                foreach (var enumObj in asEnumerable)
                {
                    if ( enumObj != null) {
                       var nestedResults = new List<ValidationResult>();
                       if (!TryValidateObjectRecursive(enumObj, nestedResults, validatedObjects, validationContextItems))
                       {
                           result = false;
                           foreach (var validationResult in nestedResults)
                           {
                               PropertyInfo property1 = property;
                               results.Add(new ValidationResult(validationResult.ErrorMessage, validationResult.MemberNames.Select(x => property1.Name + '.' + x)));
                           }
                       };
                    }
                }
            }
            else
            {
                var nestedResults = new List<ValidationResult>();
                if (!TryValidateObjectRecursive(value, nestedResults, validatedObjects, validationContextItems))
                {
                    result = false;
                    foreach (var validationResult in nestedResults)
                    {
                        PropertyInfo property1 = property;
                        results.Add(new ValidationResult(validationResult.ErrorMessage, validationResult.MemberNames.Select(x => property1.Name + '.' + x)));
                    }
                };
            }
        }

        return result;
    }
}



public class ValidateObjectAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var results = new List<ValidationResult>();
        var context = new ValidationContext(value, null, null);

        Validator.TryValidateObject(value, context, results, true);

        if (results.Count != 0)
        {
            var compositeResults = new CompositeValidationResult(String.Format("Validation for {0} failed!", validationContext.DisplayName));
            results.ForEach(compositeResults.AddResult);

            return compositeResults;
        }

        return ValidationResult.Success;
    }
}

public class ValidateCollectionAttribute : ValidationAttribute
{
    public Type ValidationType { get; set; }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var collectionResults = new CompositeValidationResult(String.Format("Validation for {0} failed!",
                       validationContext.DisplayName));
        var enumerable = value as IEnumerable;

        var validators = GetValidators().ToList();

        if (enumerable != null)
        {
            var index = 0;

            foreach (var val in enumerable)
            {
                var results = new List<ValidationResult>();
                var context = new ValidationContext(val, validationContext.ServiceContainer, null);

                if (ValidationType != null)
                {
                    Validator.TryValidateValue(val, context, results, validators);
                }
                else
                {
                    Validator.TryValidateObject(val, context, results, true);
                }

                if (results.Count != 0)
                {
                    var compositeResults =
                       new CompositeValidationResult(String.Format("Validation for {0}[{1}] failed!",
                          validationContext.DisplayName, index));

                    results.ForEach(compositeResults.AddResult);

                    collectionResults.AddResult(compositeResults);
                }

                index++;
            }
        }

        if (collectionResults.Results.Any())
        {
            return collectionResults;
        }

        return ValidationResult.Success;
    }

    private IEnumerable<ValidationAttribute> GetValidators()
    {
        if (ValidationType == null) yield break;

        yield return (ValidationAttribute)Activator.CreateInstance(ValidationType);
    }
}

public class CompositeValidationResult : ValidationResult
{
    private readonly List<ValidationResult> _results = new List<ValidationResult>();

    public IEnumerable<ValidationResult> Results
    {
        get
        {
            return _results;
        }
    }

    public CompositeValidationResult(string errorMessage) : base(errorMessage) { }
    public CompositeValidationResult(string errorMessage, IEnumerable<string> memberNames) : base(errorMessage, memberNames) { }
    protected CompositeValidationResult(ValidationResult validationResult) : base(validationResult) { }

    public void AddResult(ValidationResult validationResult)
    {
        _results.Add(validationResult);
    }
}


public interface IDataAnnotationsValidator
{
    bool TryValidateObject(object obj, ICollection<ValidationResult> results, IDictionary<object, object> validationContextItems = null);
    bool TryValidateObjectRecursive<T>(T obj, List<ValidationResult> results, IDictionary<object, object> validationContextItems = null);
}

public static class ObjectExtensions
{
    public static object GetPropertyValue(this object o, string propertyName)
    {
        object objValue = string.Empty;

        var propertyInfo = o.GetType().GetProperty(propertyName);
        if (propertyInfo != null)
            objValue = propertyInfo.GetValue(o, null);

        return objValue;
    }
}

public class SkipRecursiveValidation : Attribute
{
}

public class SaveValidationContextAttribute : ValidationAttribute
{
    public static IList<ValidationContext> SavedContexts = new List<ValidationContext>();

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        SavedContexts.Add(validationContext);
        return ValidationResult.Success;
    }
}

I cleaned the code from j_freyre a little. The "this.serviceProvider" can be replaced with "null" if you dont have one.

    /// <summary>
    /// Validates given <paramref name="obj"/>
    /// </summary>
    /// <param name="obj"></param>
    /// <param name="items">optional items</param>
    /// <param name="validationResults">optional list of <see cref="ValidationResult"/></param>
    public bool TryValidateObject(object obj, Dictionary<object, object> items, List<ValidationResult> validationResults)
    {
        // create validation context
        ValidationContext validationContext = new ValidationContext(obj, this.serviceProvider, items);

        // do validation
        if (validationResults == null)
            validationResults = new List<ValidationResult>();
        bool result = true;

        if (!Validator.TryValidateObject(obj, validationContext, validationResults, true))
            result = false;

        // do validation of nested objects
        if (obj == null)
            return result;


        // get properties that can be validated
        List<PropertyInfo> properties = obj.GetType()
            .GetProperties()
            .Where(prop => prop.CanRead && prop.GetIndexParameters().Length == 0)
            .Where(prop => CanTypeBeValidated(prop.PropertyType))
            .ToList();

        // loop over each property
        foreach (PropertyInfo property in properties)
        {
            // get and check value
            var value = property.GetValue(obj);
            if (value == null)
                continue;

            // check whether its an enumerable - if not, put the value in a new enumerable
            IEnumerable<object> valueEnumerable = value as IEnumerable<object>;
            if (valueEnumerable == null)
            {
                valueEnumerable = new object[] { value };
            }

            // validate values in enumerable
            foreach (var valueToValidate in valueEnumerable)
            {
                List<ValidationResult> nestedValidationResults = new List<ValidationResult>();
                if (!TryValidateObject(valueToValidate, items, nestedValidationResults))
                {
                    result = false;

                    // add nested results to this results (so the member names are correct)
                    foreach (var validationResult in nestedValidationResults)
                    {
                        validationResults.Add(new ValidationResult(validationResult.ErrorMessage, validationResult.MemberNames.Select(x => property.Name + '.' + x)));
                    }
                }
            }
        }


        return result;
    }

    /// <summary>
    /// Returns whether the given <paramref name="type"/> can be validated
    /// </summary>
    private bool CanTypeBeValidated(Type type)
    {
        if (type == null)
            return false;
        if (type == typeof(string))
            return false;
        if (type.IsValueType)
            return false;

        if (type.IsArray && type.HasElementType)
        {
            Type elementType = type.GetElementType();
            return CanTypeBeValidated(elementType);
        }

        return true;
    }

Fluent Validation library provides excellent support for validating complex nested objects. So, say in your application you have Customer's, and Customer's can have collections of Orders, like this:

public class Customer 
{
  public List<Order> Orders { get; set; } = new List<Order>();
}

public class Order 
{
  public double Total { get; set; }
}

Now, to validate Customer's, all you need is to set orders validator for each Order:

public class OrderValidator : AbstractValidator<Order> 
{
  public OrderValidator() 
  {
    RuleFor(x => x.Total).GreaterThan(0);
  }
}

public class CustomerValidator : AbstractValidator<Customer> 
{
  public CustomerValidator() 
  {
    RuleForEach(x => x.Orders).SetValidator(new OrderValidator());
  }
}