[SOLVED] "The JSON value could not be converted to System.Collections.Generic.IEnumerable`1[StudentsManagementSystem.Entity.CreateStudentEntity]

Issue

I am new to .NET and the MVC architecture. I am working on a mini project to create API for students information processing. However, I encountered the following error while attempting to create a collection of new students using curl:

{"type":"https://tools.ietf.org/html/rfc7231#section-6.5.1","title":"One or more validation errors occurred.","status":400,"traceId":[REDACTED],"errors":{"$":["The JSON value could not be converted to System.Collections.Generic.IEnumerable`1[StudentsManagementSystem.Entity.CreateStudentEntity]. Path: $ | LineNumber: 0 | BytePositionInLine: 1."]}}

Here’s the Controller class that should handle the request:

namespace StudentsManagementSystem.StudentController{
[ApiController]
[Route("api/student/Collections")]
public class StudentCollectionController: ControllerBase
{
    private IStudentRepository _students;
    private IMapper _mapper;
    public StudentCollectionController(IMapper mapper, IStudentRepository student)
    {
        _mapper = mapper;
        _students = student;
    }

    [HttpPost]
    public ActionResult<IEnumerable<Student>> CreateStudentCollection(IEnumerable<CreateStudentEntity> newStudents)
    {
        Console.WriteLine("DEBUGG");
        if (newStudents.Count<CreateStudentEntity>()< 1) return BadRequest();
        var map = _mapper.Map<IEnumerable<Student>>(newStudents);
        foreach(var student in map)
        {
            _students.AddStudent(student);
        }
        return Ok();
    }
}

The CreateStudentEntity Class:

namespace StudentsManagementSystem.Entity{
public class CreateStudentEntity
{
    public string StudentName { get; set; }

    public string MatricNo { get; set; }
    public string Level { get; set; }
    public string Dept { get; set; }
    public DateTime DoB { get; set; }
    public int YOA { get; set; }
    public ICollection<Course> Results { get; set; } = new List<Course>();
}

Student Entity class:

namespace StudentsManagementSystem.Entity{
public class Student
{
    public string StudentName { get; set; }
    public int StudentId { get; set; }
    public string MatricNo { get; set; }
    public string Level { get; set; }
    public string Dept { get; set; }
    public DateTime DoB { get; set; }
    public int YOA { get; set; }
    public ICollection<Course> Results { get; set; } = new List<Course>();


}

The curl request:

curl -X POST http://localhost:5000/api/student/collections -H "Content-Type:application/json" -d "{{}}"

Note:DEBUGG was not written on the console.

Kindly help a n00b 🙁

Solution

The value you’re sending in the cURL request – {{}} – isn’t valid JSON and doesn’t represent an array. Arrays in JSON are represented by square brackets [] and objects by curly brackets {}.

So, if you want to pass an empty array to the controller you’d use [].

If you want to pass an array containing an empty object it would be [{}], eg:

curl -X POST http://localhost:5000/api/student/collections -H "Content-Type:application/json" -d "[{}]"

To pass CreateStudentEntity objects in the array you’d need to include the properties, eg:

[{"MatricNo": "ABC123", "StudentId": 123, ...}, {object2...}, ...]

Answered By – haldo

Answer Checked By – David Goodson (BugsFixing Volunteer)