創建基於ASP.NET core 3.1的RazorPagesMovie項目（四）-使用數據庫

本節介紹數據庫上下文

1、打開/Data/RazorPagesMovieContent.cs 、Startup.cs文件：

　　

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using RazorPagesMovie.Models;

namespace RazorPagesMovie.Data
{
    public class RazorPagesMovieContext : DbContext
    {
        public RazorPagesMovieContext (DbContextOptions<RazorPagesMovieContext> options)
            : base(options)
        {
        }

        public DbSet<RazorPagesMovie.Models.Movie> Movie { get; set; }
    }
}

 　　RazorPagesMovieContent對象負責連接到數據庫，並將Movie對象映射到數據庫中的記錄。在Start.cs文件中，ConfigureServices方法中向依賴關系注入（Dependency Injection）容器中注冊數據庫上下文，第30行：

　　

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.EntityFrameworkCore;
using RazorPagesMovie.Data;

namespace RazorPagesMovie
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddRazorPages();

            services.AddDbContext<RazorPagesMovieContext>(options =>
                    options.UseSqlServer(Configuration.GetConnectionString("RazorPagesMovieContext")));
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapRazorPages();
            });
        }
    }
}

 

　　ASP.NET Core 配置系統會從appsettings.json文件中讀取數據庫連接字符串ConnectionString：

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "RazorPagesMovieContext": "Server=(localdb)\\mssqllocaldb;Database=RazorPagesMovieContext-6047c874-bb75-49ef-b998-62db7c5cbaf4;Trusted_Connection=True;MultipleActiveResultSets=true"
  }
}

 

　　其中，Server表示服務器，這里是localdb\\mssqllocaldb；Database表示數據庫名稱，是一個系統自動生成的，數據庫名可以是任意的。在將程序部署到測試或者生產服務器時，可以使用環境變量將連接字符串設置為實際的數據庫服務器。以后再詳細介紹。

 

2、SQL Server Express LocalDB

　　localdb，是輕型版的數據庫引擎。按需啟動。默認情況下，它將在c:\用戶\你的用戶名\目錄下創建*.mdf和*_log.ldf文件。我這里生成的如下：

　　　　

 

 

　　選擇“視圖”>"SQL Server 對象資源管理器"，在對象資源管理中我們可以看到剛才生成的數據庫和表：

　　

 

 　　在dbo.Movie表上右鍵，選擇“視圖設計器”，可以查看表格結構以及對應的TSQL和表上其他的對象：

　　

 

 　　在dbo.Movie表上右鍵，選擇“查看數據”，可以查看我們新增的電影記錄：

　　

　3、設定數據庫種子（Seed the database）

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using RazorPagesMovie.Data;
using System;
using System.Linq;

namespace RazorPagesMovie.Models
{
    public static class SeedData
    {
        public static void Initialize(IServiceProvider serviceProvider)
        {
            using (var context = new RazorPagesMovieContext(
                serviceProvider.GetRequiredService<
                    DbContextOptions<RazorPagesMovieContext>>()))
            {
                // Look for any movies.
                if (context.Movie.Any())
                {
                    return;   // DB has been seeded
                }

                context.Movie.AddRange(
                    new Movie
                    {
                        Title = "When Harry Met Sally",
                        ReleaseDate = DateTime.Parse("1989-2-12"),
                        Genre = "Romantic Comedy",
                        Price = 7.99M
                    },

                    new Movie
                    {
                        Title = "Ghostbusters ",
                        ReleaseDate = DateTime.Parse("1984-3-13"),
                        Genre = "Comedy",
                        Price = 8.99M
                    },

                    new Movie
                    {
                        Title = "Ghostbusters 2",
                        ReleaseDate = DateTime.Parse("1986-2-23"),
                        Genre = "Comedy",
                        Price = 9.99M
                    },

                    new Movie
                    {
                        Title = "Rio Bravo",
                        ReleaseDate = DateTime.Parse("1959-4-15"),
                        Genre = "Western",
                        Price = 3.99M
                    }
                );
                context.SaveChanges();
            }
        }
    }
}

 

 　　第18-21行：如果DB中有任何電影，則會返回種子初始值設定項，並且不會添加任何電影。

 　　添加種子初始值設定項：

　　打開Program.cs文件，修改Main方法：

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using RazorPagesMovie.Models;
using System;

namespace RazorPagesMovie
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var host = CreateHostBuilder(args).Build();

            using (var scope = host.Services.CreateScope())
            {
                var services = scope.ServiceProvider;

                try
                {
                    SeedData.Initialize(services);
                }
                catch (Exception ex)
                {
                    var logger = services.GetRequiredService<ILogger<Program>>();
                    logger.LogError(ex, "An error occurred seeding the DB.");
                }
            }

            host.Run();

        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

 

4、測試

　　1、刪除數據庫中我們剛才錄入的數據：既可以從數據庫中直接刪除，也可以通過delete頁面進行

　　2、退出IIS Express

　　

 

 

　　3、再次按下ctrl+F5，運行。我們發現，即使我們已經完全刪除錄入的記錄，頁面上還是還是有記錄，這就是數據庫的種子：

　　

 

 

　　下一節，我們介紹數據的展示