how to validate model in asp.net core 3.1 web api post method?

Sujeet Raman

I have an api post method. I don't have any UI to use that api so i need to show my error message in postman. If I miss one property the missing property error message should be displayed in postman.i confused with many post in internet.

my post method

[HttpPost("api/Student/Check")]
public async Task Check([FromBody] students input)
{
var result = await _students.studentAsync(input);
return Ok(result);
}
my model
public class students
{
[JsonProperty("studentid")]
public int studentid{ get; set; }
[JsonProperty("studentname")]
public int studentname{ get; set; }
[JsonProperty("studentage")]
public int studentage{ get; set; }
}
}

I should get like:

Expected Result: Status code is 400 bad request and response should be as below:

student id is required.This cannot be null or blank.

student name is required.This cannot be null or blank

student age field is required.This cannot be null or blank.

5 Replies

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Sujeet Raman5y ago
i have given data annotation and i given an empty proprty also but still it showing the default message

{
"studentid": [
"Error converting value {null} to type 'System.Int32'. Path 'studentid', line 2, position 26."
]
}
+1
Kiran Mohanty5y ago
Hi,
Define your model as below.
public class Employee
{
[Required (ErrorMessage = "student Id is required.This cannot be null or blank")]
    public int StudentId { get; set; }
    [Required (ErrorMessage = "Student name is required.This cannot be null or blank")]
[StringLength(100, MinimumLength = 2)]
    public string FirstName { get; set; }
[Required]
    public string LastName { get; set; }
[Required (ErrorMessage = "Student age is required.This cannot be null or blank")]
    public int Age{ get; set; }
}
+1
Sujeet Raman5y ago
how i will get the customized error messege in postman? where i have to give the following messages

student id is required.This cannot be null or blank.
student name is required.This cannot be null or blank
student age field is required.This cannot be null or blank.

+1
Rijwan Ansari5y ago
Additionally, you can create filter for every model validation as shown
ValidatorActionFilter.cs
///

/// Filter for returning a result if the given model to a controller does not pass validation
///
public class ValidatorActionFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (!filterContext.ModelState.IsValid)
        {
            filterContext.Result = new BadRequestObjectResult(filterContext.ModelState);
        }
    }

    public void OnActionExecuted(ActionExecutedContext filterContext)
    {

    }
}
Add in Startup.cs class
public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(options =>
    {
        options.Filters.Add(typeof(ValidatorActionFilter));
    });
}
+2
Rijwan Ansari5y ago
You can validate model with Data Annotations with package

Install-Package System.ComponentModel.Annotations

Model Sample:
public class Employee

{

    public int EmployeeId { get; set; }

    [Required]

    [StringLength(100, MinimumLength = 2)]

    public string FirstName { get; set; }

    [Required]

    public string LastName { get; set; }

    [Required]

    public string Email { get; set; }

}
+2