如何使用Asp.net Core防止Blazor服务器端出现重复记录

问题描述

我在sql Server中使用Blazor服务器端。我想防止表中的重复记录。我不在sql Server中使用唯一索引。我想在插入数据库之前检查它吗？

Services.cs

using Test.Data;
using Test.Models.Moodle;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace Test.Services.Moodle
{
    public class MoodleService:IMoodleService
    {
        private readonly ApplicationDbContext _context;

        public MoodleService(ApplicationDbContext context)
        {
            _context = context;
        }
        public async Task<List<MoodleTableModel>> Get()
        {
            return await _context.MoodleTablesList.ToListAsync();
        }

        public async Task<MoodleTableModel> Get(int id)
        {
            var moodle = await _context.MoodleTablesList.FindAsync(id);
            return moodle;
        }

        public async Task<MoodleTableModel> Add(MoodleTableModel moodle)
        {
            _context.MoodleTablesList.Add(moodle);
            await _context.SaveChangesAsync();
            return moodle;
        }
        public async Task<MoodleTableModel> Update(MoodleTableModel moodle)
        {
            _context.Entry(moodle).State = EntityState.Modified;
            await _context.SaveChangesAsync();
            return moodle;
        }
        public async Task<MoodleTableModel> Delete(int id)
        {
            var moodle = await _context.MoodleTablesList.FindAsync(id);
            _context.MoodleTablesList.Remove(moodle);
            await _context.SaveChangesAsync();
            return moodle;
        }
    }
}

解决方法

您可以使用dbcontext.MoodleTableList.Any（）在插入之前检查db中是否有任何记录

,

 public async Task<bool> Add(MoodleTableModel moodle)
    {//Condition to prevent duplicate
        MoodleTableModel existingmoodle = await _dbContext.MoodleTableModel .FirstOrDefaultAsync(
m => m.Room== moodle.Room && m.Day== moodle.Day);
        if (existingmoodle != null)
        {
            
           await Delete(moodle.Id);
        }
        else
        {moodle.Id = Guid.NewGuid().ToString();
        _dbContext.Add(moodle);
        }

        try
        {
            await _dbContext.SaveChangesAsync();
            return true;
        }
        catch (DbUpdateException)
        {
            return false;
        }

    }