Asp.net 核心 Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException:

Question

i am creating simple crud system in asp.net core mvc with angular i ran into the problem with while updating the records record not updatedd.i got the error as

Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException: 
The database operation was expected to affect 1 row(s), but actually affected 0 row(s); 

i could save and delete and view the records only i had a problwm with update records.please solve the problem.

StudentController.cs

     using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using ReactAspCrud.Models;

namespace ReactAspCrud.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class StudentController : ControllerBase
    {
        private readonly StudentDbContext _studentDbContext;


        public StudentController(StudentDbContext studentDbContext)
        {
            _studentDbContext = studentDbContext;
        }

        [HttpGet]
        [Route("GetStudent")]
        public async Task<IEnumerable<Student>> GetStudents()
        {
            return await _studentDbContext.Student.ToListAsync();
        }

        [HttpPost]
        [Route("AddStudent")]
        public async Task<Student> AddStudent(Student objStudent)
        {
            _studentDbContext.Student.Add(objStudent);
            await _studentDbContext.SaveChangesAsync();
            return objStudent;
        }

        [HttpPatch]
        [Route("UpdateStudent/{id}")]
        public async Task<Student> UpdateStudent(Student objStudent)
        {
            _studentDbContext.Entry(objStudent).CurrentValues.SetValues(objStudent);
            _studentDbContext.Entry(objStudent).State= EntityState.Modified;
            await _studentDbContext.SaveChangesAsync();
            return objStudent;
        }

        [HttpDelete]
        [Route("DeleteStudent/{id}")]
        public bool DeleteStudent(int id) 
        {
            bool a = false;
            var student = _studentDbContext.Student.Find(id);
            if (student != null)
            {
                a = true;
                _studentDbContext.Entry(student).State= EntityState.Deleted;
                _studentDbContext.SaveChanges();

            }
            else
            {
                a = false;
            }

            return a;



        }

    }

}

Studentcrud.components.ts

  setUpdate(data: any) 
  {
   this.stname = data.stname;
   this.course = data.course;
   

   this.currentStudentID = data.id;
 
  }

  UpdateRecords()
  {
    let bodyData = 
    {
      "stname" : this.stname,
      "course" : this.course,
    };
    
    this.http.patch("https://localhost:7195/api/Student/UpdateStudent"+ "/"+ this.currentStudentID,bodyData).subscribe((resultData: any)=>
    {
        console.log(resultData);
        alert("Student Registered Updateddd")
        this.getAllStudent();
      
    });
  }

Answer 1

I think the problem might be that the DBContext does not know which properties changed exactly.

Use the Find() method to get the entity, then you can

_studentDbContext.Entry(existingObject)..CurrentValues.SetValues(objStudent);

Not sure if you can do the same using the Attach method too to save a call to the DB, and (if it works) update all fields whether changed or not.