学习ASP.NET Core Blazor编程系列六——初始化数据

「爱情、让人受尽委屈。」 2024-03-16 13:11 10阅读 0赞

在[学习ASP.NET Core Blazor编程系列三——实体 ][ASP.NET Core Blazor_]这篇文章中我们创建了数据库上下文BookContex类，这个类就是用于处理数据库连接和将Book实体对象映射到数据库表（Book）记录。数据库上下文(BookContext)是在Program.cs文件的builder.Services.AddDbContextFactory方法中向依赖关系注入容器进行注册，具体代码如下：

builder.Services.AddDbContextFactory<BookContext>(opt =>
    opt.UseSqlServer(ConfigHelper.Configuration["ConnectionStrings:BookContext"]));

为了进行本地开发，我们在appsettings.json 文件中配置数据库连接字符串，数据库连接配置如下：

"ConnectionStrings": {
        "BookContext": "Server=.;Database=LeaseBook;Trusted_Connection=True;
    MultipleActiveResultSets=true"
      }

将应用程序部署到测试或生产服务器时，可以修改Appsettings.json文件中上将配置，将数据库连接字符串设置为真正的SQL服务器。

在[学习ASP.NET Core Blazor编程系列四——迁移 ][ASP.NET Core Blazor_ 1]这篇文章中我们通过EF Core提供的迁移功能，创建了数据库表。

在[学习ASP.NET Core Blazor编程系列五——列表页面 ][ASP.NET Core Blazor_ 2]这篇文章我们创建了图书列表页面，不过由于数据库中没有数据，我们的图书列表页面上也是一片空白没有数据显示。

今天的这篇文章，我们将通过EF Core6提供的功能，向数据库表Book中添加初始数据。

**一、给数据库添加初始数据**

在Visual Studio 2022 的解决方案资源管理器中，使用鼠标左键选中Models文件，然后点击鼠标右键，在弹出菜单中选择“添加--》类”，创建一个新的类文件，命名为SeedData。具体代码如下：

![6a15ff4fdac59fdd48df62939049569b.gif][]

using Microsoft.EntityFrameworkCore;
    
    namespace BlazorAppDemo.Models
    {
        public class SeedData
        {
            public static void Initialize(IServiceProvider serviceProvider)
            {
                using (var context = new BookContext(serviceProvider.
    GetRequiredService<DbContextOptions<BookContext>>()))
                {
                    // Look for any Books.
                    if (context.Book.Any())
                    {
                        return;   // DB has been seeded
                    }
                   context.Book.AddRange(
                        new Book
                        {
                            Name = "Python编程 从入门到实践",
                            ReleaseDate = DateTime.Parse("2018-1-12"),
                           Author = "埃里克·马瑟斯",
                            Price = 75.99M,
                            StockQty=10,
                            Qty=0,
                            TotalPages=445,
                            Type=""
                        },
     
                        new Book
                        {
                            Name = "Java编程的逻辑",
                            ReleaseDate = DateTime.Parse("2018-1-13"),
                            Author = "马俊昌",
                            Price = 48.99M,
                              StockQty = 12,
                            Qty = 0,
                            TotalPages = 675,
                            Type = ""
                        },
                        new Book
                        {
                            Name = "统计思维:大数据时代瞬间洞察因果的关键技能",
                            ReleaseDate = DateTime.Parse("2017-12-23"),
                            Author = "西内启",
                            Price = 39.99M,
                            StockQty = 20,
                            Qty = 0,
                            TotalPages = 330,
                            Type = ""
                        }, 
    
                        new Book
                        {
                            Name = "微信营销",
                            ReleaseDate = DateTime.Parse("2018-01-05"),
                            Author = "徐林海",
                            Price = 33.99M,
                            StockQty = 30,
                            Qty = 0,
                            TotalPages = 266,
                            Type = ""
                        }
                    );
                    context.SaveChanges();
               }
            }
         }
    }

![2530d1de4927333345b7eb12a982e7f1.gif][]

以下语句的作用是 如果数据库中有Book表，数据初始化类将返回，不添加任何数据。

![f1b6c29b3f3ee0a6f82969ee2e87f77c.gif][]

// Look for any Books.
                    if (context.Book.Any())
                    {
                        return;   // DB has been seeded
                    }

![533b22cdfc47da3b5d47fd20e6abba04.gif][]

**二、添加SeedData.initializer方法**

1.在Visual Studio 2022 的解决方案资源管理器中打开Program.cs文件，然后找到Main方法，在这个方法体的最后面添加SeedData.Initialize()方法，代码如下：

![533b22cdfc47da3b5d47fd20e6abba04.gif][]

using BlazorAppDemo.Data;
    using BlazorAppDemo.Models;
    using Microsoft.AspNetCore.Components;
    using Microsoft.AspNetCore.Components.Web;
    using Microsoft.Extensions.Configuration;
    using Microsoft.EntityFrameworkCore;
    using Microsoft.Extensions.Hosting;
    
    
    var builder = WebApplication.CreateBuilder(args);
     
    
    // Add services to the container.
    
    builder.Services.AddRazorPages();
    builder.Services.AddServerSideBlazor();
    builder.Services.AddSingleton<WeatherForecastService>();
    System.Console.WriteLine(ConfigHelper.Configuration["ConnectionStrings:BookContext"]);
    builder.Services.AddDbContextFactory<BookContext>(opt =>
     opt.UseSqlServer(ConfigHelper.Configuration["ConnectionStrings:BookContext"]));
    
    var app = builder.Build();
    
    // Configure the HTTP request pipeline.
    
    if (!app.Environment.IsDevelopment())
    {
        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();
    }
    
     
    //数据库数据初始化
    using (var scope = app.Services.CreateScope())
    {
        var services = scope.ServiceProvider;
        try
        {
            Console.WriteLine("数据库开始初始化。");
            var context = services.GetRequiredService<BookContext>();
            // requires using Microsoft.EntityFrameworkCore;
            context.Database.Migrate();
            // Requires using BlazorAppDemo.Models;
            SeedData.Initialize(services);
            Console.WriteLine("数据库初始化结束。");
        }
     
        catch (Exception ex)
        {
            var logger = services.GetRequiredService<ILogger<Program>>();
            logger.LogError(ex, "数据库数据初始化错误.");
        }
    
    }
     
    app.UseHttpsRedirection();
     
    app.UseStaticFiles();
     
    app.UseRouting();
     
    app.MapBlazorHub();
    app.MapFallbackToPage("/_Host");
    app.Run();

![b1ec20712c02c05f37ac0b4880c792f6.gif][]

2.在Visual Studio 2022中的菜单上选择“生成-->开始调试”，或按F5键。运行BlazorAppDemo应用程序。如下图。将进行数据库初始化。

![a2b3469aa9de2932cdcade884d835aa1.png][]

**三、测试应用程序**

1.在Visual Studio 2022中，打开“Pages\\BookIndex.razor”文件，在此文件的顶部，输入@inject IDbContextFactory<BookContext> dbFactory，注入数据库上下文。

[2.在@code][2._code]中重写OnInitializedAsync方法 ，在组件呈现时，去查询数据库中的Book表中的数据，最终呈现在页面上。具体代码如下。

![9f994e0eb118517c4252420abba6e2f2.gif][]

@page "/BookIndex"
    @using BlazorAppDemo.Models
    @using Microsoft.EntityFrameworkCore
     
    
    @inject IDbContextFactory<BookContext> dbFactory
     
    
    <PageTitle>图书列表</PageTitle>
    
    <h3>图书列表</h3>
    
    <table class="table-responsive" width="90%">
        <tr><td>Name</td>
        <td>Author</td>
        <td>Price</td>
        <td>ReleaseDate</td>
        <td>StockQty</td>
        <td>Qty</td>
        </tr>
    
        @foreach (var item in books)
        {
            <tr> 
            <td>@item.Name</td>
            <td>@item.Author</td>
            <td>@item.Price</td>
            <td>@item.ReleaseDate</td>
            <td>@item.StockQty</td>
            <td>@item.Qty</td>
            </tr>
    
        }
    
    </table>
    
    
    @code {
    
        private   static BookContext _context;
        private List<Book> books = new List<Book>();
    
        protected override async Task OnInitializedAsync()
        {
    
            _context = dbFactory.CreateDbContext();
            books=_context.Book.ToList();
            await base.OnInitializedAsync();
        } 
    }

![4abf7d4f4afc6ff3d72eb65f6cc85ca2.gif][]

3. 在Visual Studio 2022中的菜单上选择“生成à开始调试”，或按F5键。运行BlazorAppDemo应用程序。使用鼠标右键点击浏览器中左边的菜单栏中的“图书列表”菜单，在浏览器中显示图书信息。如下图。

![8034cb26d95bd5d8923ad7716369153c.png][]

[ASP.NET Core Blazor_]: https://www.cnblogs.com/chillsrc/p/16705874.html
[ASP.NET Core Blazor_ 1]: https://www.cnblogs.com/chillsrc/p/16747434.html
[ASP.NET Core Blazor_ 2]: https://www.cnblogs.com/chillsrc/p/16750400.html
[6a15ff4fdac59fdd48df62939049569b.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/55380843be03466d9f212b934fb42b6f.png
[2530d1de4927333345b7eb12a982e7f1.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/96911a3988d2482aa1eaa4f3468b3893.png
[f1b6c29b3f3ee0a6f82969ee2e87f77c.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/50e0ece8ecba43bd839a43c84aa98b2f.png
[533b22cdfc47da3b5d47fd20e6abba04.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/66c66e7eab3542f6acc664aac09567a2.png
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[a2b3469aa9de2932cdcade884d835aa1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/35994913a37f4a1b96f461966540ce71.png
[2._code]: mailto:2.%E5%9C%A8@code
[9f994e0eb118517c4252420abba6e2f2.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/f2f56f1d3cf342e6a9938bdf836ddf9f.png
[4abf7d4f4afc6ff3d72eb65f6cc85ca2.gif]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/84759428a3dc4490898c5ee53166e53b.png
[8034cb26d95bd5d8923ad7716369153c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/f65a7284a84e45628c6a2bdd438c8435.png