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EFCore CodeFirst 适配数据库

EF6中可以直接根据代码模型生成数据库Database.SetInitializer即可

在EFCore中如何实现呢？

这项功能放在了DatabaseFacade对象中，传入数据库上下文对象实例化到一个DatabaseFacade对象

可以看到DatabaseFacade有几个方法：

 获取所有迁移的migraion数据：GetMigrations

获取待迁移的migration数据 ：GetPendingMigrations

获取已经操作的migration数据：GetAppliedMigrations

适配migration： Migrate

这中间有一个坑：efcore 貌似还不能根据模型生成数据库，而是要先添加migrations的文件，然后才能适配数据库

这里我添加了一个XXXX字段，按照正常的流程：我们需要执行命令：

dotnet ef migrations add addxxxxxx

dotnet ef database update

EFCore中的自动适配数据库的前提是添加好 新增变量的migrations文件，实际上只是efcore只帮助了我们实现了dotnet ef database update的操作

首先先操作下：dotnet ef migrations add addxxxxxx

这里我写了一个简单的中间件来说明下：

通过注册服务，添加usermap引用

 /// <summary>
        /// liyouming add 20180508
        /// </summary>
        /// <typeparam name="T">（context）上下文对象</typeparam>
        /// <param name="service">扩展服务</param>
        /// <param name="optionsAction">配置</param>
        /// <returns></returns>
        public static IServiceCollection AddEFMigrations<T>(this IServiceCollection service, Action<DbContextOptionsBuilder> optionsAction) where T : DbContext
        {
            service.AddDbContext<T>(optionsAction);
            var serviceProvider = service.BuildServiceProvider();
            service.AddSingleton<IEFMigrationsContext>(new EFMigrationsContext(serviceProvider.GetRequiredService(typeof(T)) as DbContext));
            return service;
        }

这里我们需要指导上下文对象T，并将该对象放到自定义的服务 IEFMigrationsContext 去处理下

然后扩展下IApplicationBuilder

public static IApplicationBuilder UseEFMigraions(
           this IApplicationBuilder builder,string pathstring)
        {
            builder.Map(new Microsoft.AspNetCore.Http.PathString(pathstring), app => {
                app.UseMiddleware<EFMigrationsMiddleware>(pathstring);
            });
            return builder;
        }

比较简单，需要map下地址，当我们访问的时候进入到固定页面操作

 public class EFMigrationsMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly string _pathstring;
        private IEFMigrationsContext _migrationsContext;

        public EFMigrationsMiddleware(RequestDelegate next, string pathstring, IEFMigrationsContext migrationsContext)
        {
            if (next == null)
            {
                throw new Exception(nameof(next));
            }
            _next = next;
            _pathstring = pathstring;
            _migrationsContext = migrationsContext;

        }

        public async Task Invoke(HttpContext context)
        {
            if (context.Request.PathBase == _pathstring)
            {
                var list = _migrationsContext.GetPendingMigrations();
                _migrationsContext.AutoMigration();
                string strli = string.Empty;
                foreach (var item in list)
                {
                    strli += "<li>" + item + "</li>";
                }
                await context.Response.WriteAsync("<html><body><ul>" + strli + "</ul></body></html>");
            }
            else
            {
                await _next(context);
            }
            return;





        }
    }

下面直接实现接口方法就ok了,存在待更新的migrations就执行更新

public void AutoMigration()
        {
            if (databaseFacade.GetPendingMigrations().Any())
            {
                //执行迁移
                databaseFacade.Migrate();
            }
           
        }

下面来说下使用方式：跟原有的dbcontext使用方式一样，配置好你的上下文对象配置

注册服务：

 services.AddEFMigrations<UserDbContext>(optionsBuilder =>
            {
                var _userappsetting = Configuration.Get<UserAppSetting>();
                if (_userappsetting == null)
                {
                    throw new Exception("数据库连接字符串未配置");
                }
                switch (_userappsetting.DbType)
                {
                    case 1:

                        optionsBuilder.UseSqlServer(_userappsetting.UserConnectionString, sqlserver =>
                        {
                            sqlserver.MigrationsAssembly(_migrationAssablyName);
                            sqlserver.UseRelationalNulls();
                            sqlserver.UseRowNumberForPaging();

                        });
                        break;
                    case 2:
                        optionsBuilder.UseMySQL(_userappsetting.UserConnectionString, mysql =>
                        {
                            mysql.MigrationsAssembly(_migrationAssablyName);
                            mysql.UseRelationalNulls();
                        });
                        break;
                    default:
                        optionsBuilder.UseSqlServer(_userappsetting.UserConnectionString, sqlserver =>
                        {
                            sqlserver.MigrationsAssembly(_migrationAssablyName);
                            sqlserver.UseRelationalNulls();
                            sqlserver.UseRowNumberForPaging();
                        });
                        break;
                }
            });
AddEFMigrations

添加Configure

 app.UseEFMigraions("/Migrations");

下面访问下：/Migrations ，这里上面的代码中我先获取了待更新的migraions 方便验证，这里可以看到待验证的migraions是我新添加 addxxxxxxx

下面我们来检查数据生成情况： 已经生成了 XXXXX字段

 

 

 如果能不操作dotnet ef migrations add addxxxxxx就好了，感觉还是有点鸡肋~~~

 

posted @ 2018-05-08 18:14  龙码精神  阅读(1924)  评论(0)  编辑  收藏  举报