aspnet core controller datetime parameter bypasses modelvalid check - datetime

Question

I have a number of controllers of this form:
public IActionResult GetSomething(int id, DateTime from) {
...
}
The id and from parameters are given on the query as query parameters. If id is not supplied, the ModelValid state is set to false. But if from is not supplied, ModelValid is true and from is set to 1900-01-01 00:00:00 (DateTime.Min).
How do I make ModelState false if a wanted DateTime parameter isn't supplied?

Answer 1

I decided to go for implementing a DateTime model binder. The following code will not set IsValid=true on ModelState if the DateTime argument is missing. DateTime? (nullable DateTime) is handled fine, but again, if the query parameter is missing, IsValid is set to false instead of setting the parameter to a default value.
First the DateTimeModelBinderProvider:
public class DateTimeModelBinderProvider : IModelBinderProvider
{
/// <inheritdoc />
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (!context.Metadata.IsComplexType)
{
// We can handle DateTime and nullable DateTime
if ((context.Metadata.ModelType == typeof(DateTime)) ||
(context.Metadata.IsNullableValueType && context.Metadata.UnderlyingOrModelType == typeof(DateTime)))
return new DateTimeModelBinder(context.Metadata.ModelType);
}
return null;
}
}
Next the DateTimeModelBinder. Most of the code is copied verbatim from github. Some of it could be left out, but it works as it is:
public class DateTimeModelBinder : IModelBinder
{
private readonly TypeConverter _typeConverter;
public DateTimeModelBinder(Type type)
{
if (type == null)
{
throw new ArgumentNullException(nameof(type));
}
_typeConverter = TypeDescriptor.GetConverter(type);
}
/// <inheritdoc />
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null)
{
throw new ArgumentNullException(nameof(bindingContext));
}
var valueProviderResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
if (valueProviderResult == ValueProviderResult.None)
{
// Do not accept an empty value provider result as being ok for DateTime (is ok for DateTime?)
bindingContext.ModelState.TryAddModelError(
bindingContext.ModelName,
bindingContext.ModelMetadata.ModelBindingMessageProvider.ValueMustNotBeNullAccessor(
valueProviderResult.ToString()));
// no entry
return Task.CompletedTask;
}
bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);
try
{
var value = valueProviderResult.FirstValue;
object model = null;
if (!string.IsNullOrWhiteSpace(value))
{
model = new DateTimeConverter().ConvertFrom(
context: null,
culture: valueProviderResult.Culture,
value: value);
}
if (bindingContext.ModelType == typeof(string))
{
var modelAsString = model as string;
if (bindingContext.ModelMetadata.ConvertEmptyStringToNull &&
string.IsNullOrEmpty(modelAsString))
{
model = null;
}
}
// When converting newModel a null value may indicate a failed conversion for an otherwise required
// model (can't set a ValueType to null). This detects if a null model value is acceptable given the
// current bindingContext. If not, an error is logged.
if (model == null && !bindingContext.ModelMetadata.IsReferenceOrNullableType)
{
bindingContext.ModelState.TryAddModelError(
bindingContext.ModelName,
bindingContext.ModelMetadata.ModelBindingMessageProvider.ValueMustNotBeNullAccessor(
valueProviderResult.ToString()));
return Task.CompletedTask;
}
else
{
bindingContext.Result = ModelBindingResult.Success(model);
return Task.CompletedTask;
}
}
catch (Exception exception)
{
var isFormatException = exception is FormatException;
if (!isFormatException && exception.InnerException != null)
{
// TypeConverter throws System.Exception wrapping the FormatException,
// so we capture the inner exception.
exception = ExceptionDispatchInfo.Capture(exception.InnerException).SourceException;
}
bindingContext.ModelState.TryAddModelError(
bindingContext.ModelName,
exception,
bindingContext.ModelMetadata);
// Were able to find a converter for the type but conversion failed.
return Task.CompletedTask;
}
}
}
Also remember to activate it. I insert it at the start of the provider list to ensure my DateTime provider is used in preference of the default handler:
var mvc = services.AddMvc(config => {
config.ModelBinderProviders.Insert(0, new DateTimeModelBinderProvider());
});

Answer 2

You can solve this issue by creating a model that has a validation attribute for the 'From' property.
I havent tested out the code. But code should be like:
public class Model
{
public int Id { get; set; }
[DateTimeShouldHaveValue]
public DateTime From { get; set; }
}
public class DateTimeShouldHaveValueAttribute : ValidationAttribute
{
public override bool IsValid(object value)
{
if (value == null)
return false;
var dateTimeTmp = value.ToString();
DateTime dateTime;
DateTime.TryParse(dateTimeTmp, out dateTime);
if (dateTime == DateTime.MinValue)
return false;
return true;
}
}
public IActionResult GetSomething(Model model)
{
}