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FromBody annotation is not able to access field from request body

I created a sample .NET Core Web API and provide an endpoint to create a new task for yourself. So the endpoint would be
POST ...baseUrl.../me/tasks
The method for this is
[HttpPost("tasks")]
public async Task<ActionResult<Task>> CreateUserTaskAsync([FromBody] CreateUserTaskBodyDto createUserTaskBodyDto)
{
// ...
}
As you can see the parameter is a DTO which deals with the request validation for the body. This DTO currently has one field but there might be more fields later on
public class CreateUserTaskBodyDto
{
[Range(1, 30)]
public string Name { get; set; }
}
When calling the url with the following body
{
"name": "abc"
}
I get a 400 with the error
"errors": {
"Name": [
"The field Name must be between 1 and 30."
]
}
(I also tried it by renaming "name" to "Name"). I'm testing the API with Postman, this screenshot shows my request setup
Does someone know what's wrong or missing here?

If you remove the
[Range(1, 30)]
attribute it should work
Also if you want to validate the length of the name property you should use StringLenghtAttribute
[StringLength(30, MinimumLength = 1, ErrorMessage = "Name must be between 3 and 50 character in length.")]

According to Microsoft docs Range Attribute
Range attribute specifies the numeric range constraints for the value of a data field.
If you want to specify max and min string length. See MinLengthAttribute
[MinLength(1)]
[MaxLength(30)]
public string Name { get; set; }

.Net core ModelBinding does not Invalidate ModelState for primitive values?

I'm using .Net Core 3. I have a controller with [ApiController] attribute on it. So it returns BadRequest Error if Model Validation fails, automatically. But I have primitive values in my models like int, bool, and if I don't include these values in my request object, the ApiController does not produce an error in this case. But initializes these fields to default value. I want it to produce BadRequest Error. How can I do this?
I made the fields nullable and it worked but I don't want to make them nullable. Please help me. Thanks.
Edit:
public class AddEmployeeReqObject
{
[Required]
[JsonPropertyName("casino_id")]
[Display(Name = "casino_id")]
public long CasinoId { get; set; }
[Required]
[JsonPropertyName("name")]
[Display(Name = "name")]
public string Name { get; set; }
[Required]
[JsonPropertyName("yubico_key")]
[Display(Name = "yubico_key")]
public string YubicoKey { get; set; }
[Required]
[JsonPropertyName("is_manager")]
[Display(Name = "is_manager")]
public bool IsManager { get; set; }
}
Here IsManager and CasinoId are initialized by default with false and 0.

You should use BindRequiredAttribute instead of RequiredAttribute. RequiredAttribute works perfect for nullable-types, but for non-nullable it has no effect. For example for int the default value is 0 and the property can never be null. Even if the client submits a request where the property is completely missing, the model instance would have a value 0.
BindRequiredAttribute comes to action!
It works the same way as RequiredAttribute, except it mandates that the value comes from the request – so it not only rejects null values, but also “unbound” values.
For examples visit: https://www.strathweb.com/2017/12/required-and-bindrequired-in-asp-net-core-mvc/

I don’t know why you both set the default value for the fields, but
also want to judge it's default value as null and verify as an error.
While verifying ModelState.IsValid, you can determine whether the two fields of the model are the default values you set. If yes, then fail the verification and return BadRequest Error.
public async Task<IActionResult> Test(AddEmployeeReqObject obj)
{
if (ModelState.IsValid && obj.CasinoId != 0 && obj.IsManager)
{
return Ok();
}
else
{
return BadRequest();
}
}

int and bool variables cannot be null so to check them you have to:
make them nullable and test if they are null
or
set the bool field true (precheck the checkbox or sth) and set the int to a negative value

Integer validation against non-required attributes in MVC

I've trying to validate a property on a model I have. This property is NOT required, and so if its invalid MVC seems to be ignoring it. I've even created a custom ValidationAttribute, but nothing works.
public class NumberWang : ValidationAttribute
{
public override bool IsValid(object value)
{
if (value == null)
return true;
int g;
if (int.TryParse(value.ToString(), out g))
{
if (g >= 0)
return true;
}
return false;
}
}
public class MyModel
{
[Range(0, 999999, ErrorMessage = "category_id must be a valid number")]
[NumberWang(ErrorMessage = "That's NumberWang!")]
public int? category_id { get; set; }
/* there are other properties of course, but I've omitted them for simplicity */
public void Validate()
{
Validator.TryValidateProperty(this.category_id,
new ValidationContext(this, null, null) { MemberName = "category_id" },
this.validation_results);
}
}
If I pass the value 'abc' as a category_id to this model, it validates just fine. What am I doing wrong?

I found an ugly workaround.
It seems that if category_id is a nullable int? and my value is not a valid number, a null value is passed, and the model doesn't see the invalid 'abc' value.
[Range(0, 999999, ErrorMessage = "category_id must be a valid number")]
public int? category_id { get; set; }
// when we pass a good number
MyAction?category_id=123
validation: successful
// when we pass a bad number
// validation ignores it. not what we want.
MyAction?category_id=abc
validation: successful
If I change category_id to a non-nullable int, it fails validation even when no value is passed.
[Range(0, 999999, ErrorMessage = "category_id must be a valid number")]
public int? category_id { get; set; }
// when we pass a good number
MyAction?category_id=123
validation: successful
// when we pass an bad number
MyAction?category_id=abc
validation: "category_id must be a valid number"
// BUT, when we don't pass any number at all ...
MyAction
validation: "category_id must be a valid number"
The Ugly Workaround
If I change category_id to a string, and then only convert it to an int when I need it, I can validate it properly, using only [Range]
[Range(0, 999999, ErrorMessage = "category_id must be a valid number")]
public string category_id { get; set; }
// when we pass a good number
MyAction?category_id=123
validation: successful
// when we pass a bad number
MyAction?category_id=abc
validation: "category_id must be a valid number"
// no number, no validation. hooray!
MyAction
validation: successful
It's ugly, but it works.
(Note: the custom attribute was not needed, so I removed it and just used [Range])

model:
// "(\s*[0-9]{0,6})" for 999999 max
// "(\s*[0-9]*)" for "infinite"
[RegularExpression(#"(\s*[0-9]{0,6})", ErrorMessage = "Field must be a natural number (max 999999)")]
public int? Quantity { get; set; }
view:
#Html.TextBoxFor(m => m.Quantity)
#Html.ValidationMessageFor(m => m.Quantity)

First your model should implement IValidatableObject, but the Validate method is going to be called only if the ModelState is valid. This link can help.
Are you receiving your model as a parameter in the action? Are you asking for the ModelState.IsValid? This should work fine with the Default model binder.

I found a workaround that I kind of like. The problem I ran into was a similar issue, where the value had to be greater than 0 and a number, so once I tried to cast the 9999999999 (invalid) string as a number it threw an exception and didn't show that the model state has an error message on the post. I hope this is on topic since it sounds like "Rules don't seem to apply correctly when I type in an invalid number"
Since my number had to be positive I intercepted the value into an anonymous type object (dynamic) and used it as an intercepting body between the model's user and the private int property. When I did that, the Data Annotations worked as expected.
public dynamic MyProperty
{
get { return _myProperty; }
set
{
try
{
/I have to convert the value to String because it comes in as String[], and if there is more than one value then it should be problematic, so you join it together with an invalid character and throw an error, or you take the first value/
_myProperty = = Convert.ToInt32(String.Join("a",value));
}
catch (Exception e)
{
_myProperty= -1;
}
}
}
private int _myProperty;

Unit Testing with ASP.NET MVC 3 + Data Annotations and property DateTime

I'm on a project with DataAnnotations and ASP.NET MVC3. We use this solution to test the validations of "Date Annotions": http://gcbyjm.blogspot.com.br/2011/02/how-to-unit-test-dataannotations.html
I have problems to test a property "DateTime" of "ViewModel".
public class AchievementVM
{
...
[Required(ErrorMessage = "The date field is required.")]
[DataType(DataType.DateTime, ErrorMessage = "Invalid date.")]
public DateTime Date { get; set; }
...
}
[TestMethod]
public void AchievementVMValidator_ShouldHaveErrorWhenDateIsInvalid()
{
// Arrange
var achievementVM = new AchievementVM() { Date = ???? };
// Act
var errors = ValidationBuddy.GetErrors(achievementVM) as List<ErrorInfo>;
// Assert
ErrorInfo error = errors.Find(delegate(ErrorInfo e) { return e.ErrorMessage == "The date field is required."; });
Assert.IsTrue(error != null);
}
My question is how to pass the value of this property to simulate the ModelBind ERROR. In both situations, textbox empty and invalid data.
Thanks a lot!

If I understand your question correctly I think you should be testing action method that gets called by the view where the field is located. Like that you can pass invalid or empty values to the action method replicating empty or invalid values.

Remember that your view-model should be a representation of your view. So if your view allows a DateTime to not be entered (empty text box) then I think your view-model should have a nullable DateTime.
public DateTime? MyProperty { get; set; }
That way, in your unit test you can test for a null DateTime.
On your domain model this should be different as you dont want your database to receive a null DateTime so the domain model property should not be nullable. you view-model validation should stop the null date getting passed to the domain model or something converts it to a DateTime the domain model can handle. Maybe, for example, a null DateTime gets converted to DateTime.Now if your business requirements match this.
I hope this helps.

asp.net mvc int property bind exception

I have a int property in my class and want to validate if the user has entered a string.
How can I do that using data annotations?
When I pass a non-integer value I get a excpetion like this:
The value 'asdasd' is not valid for property.
For example using this validation attribute:
[Range(0, Int32.MaxValue, ErrorMessage="Invalid Number")]
public int? Number { get; set; }
and entering 'aaa' in a field tha uses the model I've got an excepetion with this message:
The value 'aaa' is not valid for Number.
Instead of the "Invalid Number" message.
Any Ideas?
I've put
[Range(0, Int32.MaxValue, ErrorMessage="Invalid Number")]
public int? Number { get; set; }
but I've got this message from an excpetion
The value 'aaa' is not valid for Number.

There are two stages of validation at play here.
Before the validation set up in your attributes is called, the framework first attempts to parse the information.
So here are a couple of examples based on this code:
[Range(0, Int32.MaxValue, ErrorMessage="Invalid Number")]
public int? Number { get; set; }
I type nothing into the box...
"Invalid Number" (Framework will create a null integer, your validation rule fails)
I type "A" into the box...
"The value 'A' is not valid for Number." (Framework cannot convert "A" into a nullable int, so the framework validation rule fails and your validation rule it not checked.
** Solutions **
1 - Live with the default message until you are using MVC 3 / .NET 4, which makes it easier to override these messages
2 - Exclude the value from the binder, so it won't cause an error (but you will have to bind it and check it yourself)
[Bind(Exclude="MyNumber")]
3 - Make it a string on the model, then test it with a TryParse and add your own custom model error (This is a reasonable practice and reminds us all why View Models are used rather than Domain Objects!)
if (!Int32.TryParse("MyNumber", out myInteger)) {
ModelState.AddModelError("MyNumber", "That isn't a number!");
}
There are actually lots of solutions, but I would say go with option 3 for now.

You could put a Range-attribute on your model-field like so:
[Range(0, 9999)]
public int Something {get; set;}
Now whenever the user inputs a string it will not validate, and also the int must be between 0-9999
this should also work with
[Range(0, 9999)]
public string Something {get; set;}
and
[Range(0, 9999)]
public object Something {get; set;}