【ASP.NET Core快速入门】（十六）MVC开发：DbContextSeed初始化

前言

由于我们现在每次EF实体模型变化的时候每次都是手动更改，我们想通过代码的方式让他自动更新，或者程序启动的时候添加一些数据进去

DbContextSeed初始化

首先，在Data文件夹下添加一个ApplicationDbContextSeed.cs初始化类

using Microsoft.AspNetCore.Identity;
using MvcCookieAuthSample.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;

namespace MvcCookieAuthSample.Data
{
    public class ApplicationDbContextSeed
    {
        private UserManager<ApplicationUser> _userManager;

        public async Task SeedAsync(ApplicationDbContext context, IServiceProvider services)
        {
            if (!context.Users.Any())
            {
                _userManager = services.GetRequiredService<UserManager<ApplicationUser>>();

                var defaultUser = new ApplicationUser
                {
                     UserName="Administrator",
                     Email="786744873@qq.com",
                     NormalizedUserName="admin"
                };

                var result= await _userManager.CreateAsync(defaultUser,"Password$123");
                if (!result.Succeeded)
                {
                    throw new Exception("初始默认用户失败");
                }
            }
        }
    }
}

那么如何调用呢？接下来我们写一个WebHost的扩展方法类WebHostMigrationExtensions.cs来调用ApplicationDbContextSeed方法

using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

namespace MvcCookieAuthSample.Data
{
    public static class WebHostMigrationExtensions
    {
        public static IWebHost MigrateDbContext<TContext>(this IWebHost host, Action<TContext, IServiceProvider> sedder) where TContext : DbContext
        {
            using (var scope=host.Services.CreateScope())
            {//只在本区间内有效
                var services = scope.ServiceProvider;
                var logger = services.GetRequiredService<ILogger<TContext>>();
                var context = services.GetService<TContext>();

                try
                {
                    context.Database.Migrate();
                    sedder(context, services);

                    logger.LogInformation($"执行DBContext {typeof(TContext).Name} seed执行成功");
                }
                catch (Exception ex)
                {
                    logger.LogError(ex, $"执行DBContext {typeof(TContext).Name} seed方法失败");
                }
            }

            return host;
        }
    }
}