如何使用异步task<iactionresult>将数据记录到具有实体框架的多对多表中

using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

public class Student
{
    public int StudentId { get; set; }
    public string Name { get; set; }
    // other properties

    public ICollection<Enrollment> Enrollments { get; set; }
}

public class Course
{
    public int CourseId { get; set; }
    public string Title { get; set; }
    // other properties

    public ICollection<Enrollment> Enrollments { get; set; }
}

public class Enrollment
{
    public int StudentId { get; set; }
    public int CourseId { get; set; }

    public Student Student { get; set; }
    public Course Course { get; set; }
}

public class SchoolContext : DbContext
{
    public SchoolContext(DbContextOptions<SchoolContext> options)
        : base(options)
    {
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Course> Courses { get; set; }
    public DbSet<Enrollment> Enrollments { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Enrollment>()
            .HasKey(e => new { e.StudentId, e.CourseId });
    }
}

public class EnrollmentController : ControllerBase
{
    private readonly SchoolContext _context;

    public EnrollmentController(SchoolContext context)
    {
        _context = context;
    }

    [HttpPost]
    public async Task<IActionResult> AddEnrollment(int studentId, int courseId)
    {
        var student = await _context.Students.FindAsync(studentId);
        var course = await _context.Courses.FindAsync(courseId);

        if (student == null || course == null)
        {
            return NotFound();
        }

        var enrollment = new Enrollment
        {
            StudentId = studentId,
            CourseId = courseId
        };

        _context.Enrollments.Add(enrollment);
        await _context.SaveChangesAsync();

        return Ok();
    }
}