使用EntityFramework Core和Enums作为字符串的ASP.NET Core Razor页面——第三部分

目录

介绍

使用代码

---

添加项目和项目状态处理

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介绍

这是一篇由多部分组成的文章的第三部分，演示了通过EntityFramework Core 2.1（EF）将C＃enum值映射到数据库表中的string值。它解决了enum与应用程序实体的一对多和多对多关系中的值映射问题。它在ASP.NET Core Razor Page应用程序的上下文中执行此操作。

EF是对象关系映射器（ORM）。在诸如此示例的应用程序中，有两个“世界”。一个是在C＃中作为对象模型存在的对象世界。另一个是存在于关系数据库中的关系世界，如Microsoft SQL Server。这两个世界并不一致。ORM的功能，如EntityFramework，就是这两个世界之间的桥梁，并促进它们之间的数据传输。

第一部分。设置实体框架数据上下文和初始Customer的Razor页面

第二部分。完成了Customers的CRUD功能

在第三部分。我们将创建Project和ProjectState实体并在ProjectState和Project之间实现一个一对多的关系，如下：

• 添加Project，ProjectState和ProjectStateDescription实体。
• 添加EF迁移以在数据库中创建和配置Projects和ProjectStateDescriptions表。
• 演示enum对象模型实体中的string值与Projects和ProjectStateDescriptions数据库表中的值之间的转换。
• 搭建，实现和测试包含ProjectState功能的ProjectCRUD页面，如CustomerProjects.cshtml，CustomerProjectCreate.cshtml，CustomerProjectDetails.cshtml和CustomerProjectDelete.cshtml Razor页面。

使用代码

添加初始项目处理。

接下来，我们启用Customer项目处理。该应用程序使用Customer作为“网关”实体; 一切都是通过Customer。Customer和Projects之间存在一对多的关系。因此，我们需要修改Customer类。

修改后的Customer.cs：

1.  
   using System.Collections.Generic;
2.  
    
3.  
   namespace QuantumWeb.Model
4.  
   {
5.  
   /// <summary>
6.  
   /// Customer Class
7.  
   /// </summary>
8.  
   public class Customer
9.  
   {
10.  
    #region Constructors
11.  
     
12.  
    /// <summary>
13.  
    /// Parameter-less Constructor
14.  
    /// </summary>
15.  
    /// <remarks>
16.  
    /// Required for scaffolding the UI
17.  
    /// </remarks>
18.  
    public Customer()
19.  
    {
20.  
    } // end public Customer()
21.  
     
22.  
    #endregion // Constructors
23.  
     
24.  
    /// <summary>
25.  
    /// Customer Identifier, primary key
26.  
    /// </summary>
27.  
    public int CustomerId { get; set; }
28.  
    /// <summary>
29.  
    /// Customer Name
30.  
    /// </summary>
31.  
    public string CustomerName { get; set; }
32.  
    /// <summary>
33.  
    /// Primary Customer Contact
34.  
    /// </summary>
35.  
    public string CustomerContact { get; set; }
36.  
    /// <summary>
37.  
    /// Customer Contact Phone Number
38.  
    /// </summary>
39.  
    public string CustomerPhone { get; set; }
40.  
    /// <summary>
41.  
    /// Customer Contact Email Address
42.  
    /// </summary>
43.  
    public string CustomerEmail { get; set; }
44.  
     
45.  
    #region Navigation Properties
46.  
     
47.  
    /// <summary>
48.  
    /// List of Projects
49.  
    /// </summary>
50.  
    public List<Project> Projects { get; set; }
51.  
     
52.  
    #endregion // Navigation Properties
53.  
     
54.  
    } // end public class Customer
55.  
     
56.  
    } // end namespace QuantumWeb.Model

我们添加了一个项目列表。在这里，我们将某些属性标识为导航属性。这些属性引用其他类/实体，以便我们可以在处理中导航到它们。Customer在Projects列表中表示零或多个Projects。初始Project类定义如下。

初始Project.cs：

1.  
   namespace QuantumWeb.Model
2.  
   {
3.  
   /// <summary>
4.  
   /// Project Class
5.  
   /// </summary>
6.  
   public class Project
7.  
   {
8.  
   /// <summary>
9.  
   /// Project Identifier, primary key
10.  
    /// </summary>
11.  
    public int ProjectId { get; set; }
12.  
    /// <summary>
13.  
    /// Project Name
14.  
    /// </summary>
15.  
    public string ProjectName { get; set; }
16.  
     
17.  
    #region Navigation Properties
18.  
     
19.  
    /// <summary>
20.  
    /// Customer Identifier
21.  
    /// </summary>
22.  
    public int CustomerId { get; set; }
23.  
     
24.  
    /// <summary>
25.  
    /// Customer
26.  
    /// </summary>
27.  
    /// <remarks>
28.  
    /// Every Project has a Customer
29.  
    /// </remarks>
30.  
    public Customer Customer { get; set; }
31.  
     
32.  
    /// <summary>
33.  
    /// Project Status Code
34.  
    /// </summary>
35.  
    public ProjectState ProjectStateCode { get; set; }
36.  
     
37.  
    /// <summary>
38.  
    /// ProjectStateDescription Reference
39.  
    /// </summary>
40.  
    public ProjectStateDescription ProjectStateDescription { get; set; }
41.  
     
42.  
    #endregion // Navigation Properties
43.  
     
44.  
    } // end public class Project
45.  
     
46.  
    } // end namespace QuantumApp.Model

除了定义初始化Project类之外，我们还将在Model文件夹中定义ProjectState enum。

ProjectState.cs：

1.  
   namespace QuantumWeb.Model
2.  
   {
3.  
   /// <summary>
4.  
   /// Project State Enumeration
5.  
   /// </summary>
6.  
   public enum ProjectState
7.  
   {
8.  
   Prospect,
9.  
   UnderReview,
10.  
    StartScheduled,
11.  
    InProgress,
12.  
    Completed
13.  
    } // end public enum ProjectState
14.  
     
15.  
    } // end namespace QuantumWeb.Model

这个enum指定了Project工作流的状态。

• Prospect。这涉及一个有前景的Project。这个Project可能是通过推荐或其他营销工作提出的。尚未进行任何研究，且规格尚不清楚。
• UnderReview。在这种状态下，Project制定了要求，初始预算和进度表。没有承诺Quantum或者Customer。
• StartScheduled。已经指定了工作开始的日期，并且正在准备开始工作。
• InProgress。实际工作已经开始但尚未完成。
• Completed。项目工作完成。

如前所述，我们对此应用程序有两个目标。

1. 我们应该为Project将在UI中显示的每个状态定义简短描述，以帮助用户理解每个状态的含义。
2. 每个enum值都作为string类型存储在数据库中。

为了满足ProjectState enum的这些要求，我们定义了ProjectStateDescription类。

ProjectStateDescription.cs：

1.  
   using System.Collections.Generic;
2.  
    
3.  
   namespace QuantumWeb.Model
4.  
   {
5.  
   /// <summary>
6.  
   /// Project State Description Class
7.  
   /// </summary>
8.  
   public class ProjectStateDescription
9.  
   {
10.  
    /// <summary>
11.  
    /// ProjectState Code
12.  
    /// </summary>
13.  
    public ProjectState ProjectStateCode { get; set; }
14.  
     
15.  
    /// <summary>
16.  
    /// State Description
17.  
    /// </summary>
18.  
    public string StateDescription { get; set; }
19.  
     
20.  
    #region Navigation Properties
21.  
     
22.  
    /// <summary>
23.  
    /// Projects Collection
24.  
    /// </summary>
25.  
    public List<Project> Projects { get; set; }
26.  
     
27.  
    #endregion // Navigation Properties
28.  
     
29.  
    } // end public class ProjectStateDescription
30.  
     
31.  
    } // end namespace QuantumWeb.Model

ProjectState对Projects的一对多的关系，通过导航属性启用。每个Project都有一个ProjectStateDesciption。每个ProjectStateDescripton都有一个Projects集合。

接下来，我们需要为Project和ProjectStateDescription定义EF配置类，并在QuantumDbContext类中包含所有内容。所有此活动都发生在Data文件夹中。

初始ProjectConfiguration.cs：

1.  
   using System;
2.  
   using Microsoft.EntityFrameworkCore;
3.  
   using Microsoft.EntityFrameworkCore.Metadata.Builders;
4.  
   using QuantumWeb.Model;
5.  
    
6.  
   namespace QuantumWeb.Data
7.  
   {
8.  
   public class ProjectConfiguration : IEntityTypeConfiguration<Project>
9.  
   {
10.  
    public void Configure(EntityTypeBuilder<Project> builder)
11.  
    {
12.  
    builder.ToTable("Projects");
13.  
    builder.HasKey(p => p.ProjectId);
14.  
    builder.Property(p => p.ProjectId)
15.  
    .HasColumnType("int");
16.  
    builder.Property(p => p.ProjectName)
17.  
    .IsRequired()
18.  
    .HasColumnType("nvarchar(80)")
19.  
    .HasMaxLength(80);
20.  
    builder.Property(p => p.CustomerId)
21.  
    .HasColumnType("int")
22.  
    .IsRequired();
23.  
    builder.HasOne(p => p.Customer)
24.  
    .WithMany(c => c.Projects)
25.  
    .HasForeignKey(p => p.CustomerId)
26.  
    .IsRequired();
27.  
    builder.Property(p => p.ProjectStateCode)
28.  
    .HasColumnType("nvarchar(15)")
29.  
    .HasDefaultValue(ProjectState.Prospect)
30.  
    .HasConversion(
31.  
    p => p.ToString(),
32.  
    p => (ProjectState)Enum.Parse(typeof(ProjectState), p));
33.  
    builder.HasOne(p => p.ProjectStateDescription)
34.  
    .WithMany(pd => pd.Projects)
35.  
    .HasForeignKey(p => p.ProjectStateCode);
36.  
    } // end public void Configure(EntityTypeBuilder<Project> builder)
37.  
     
38.  
    } // end public class ProjectConfiguration : IEntityTypeConfiguration<Project>
39.  
     
40.  
    } // end namespace QuantumWeb.Data

看看下面提取的行：

1.  
   builder.HasOne(p => p.Customer)
2.  
   .WithMany(c => c.Projects)
3.  
   .HasForeignKey(p => p.CustomerId)
4.  
   .IsRequired();

对这些行的解释是，“每个Project都有一个带有许多Projects的Customer。每个Project都映射到Projects数据库中的表，通过外键CustomerId，并且这是必需的。因此，Customer- Project关系是一对多。

在一对多ProjectStateDescription- Project关系被配置为：

1.  
   builder.HasOne(p => p.ProjectStateDescription)
2.  
   .WithMany(pd => pd.Projects)
3.  
   .HasForeignKey(p => p.ProjectStateCode);

接下来，我们将了解处理enum的值到数据库string列配置的方式。

1.  
   builder.Property(p => p.ProjectStateCode)
2.  
   .HasColumnType("nvarchar(15)")
3.  
   .HasDefaultValue(ProjectState.Prospect)
4.  
   .HasConversion(
5.  
   p => p.ToString(),
6.  
   p => (ProjectState)Enum.Parse(typeof(ProjectState), p));

这些行首先在Projects名为的表中配置一个列ProjectStateCode，类型为nvarchar(15),其默认值来自ProjectState.Prospect。接下来，定义ProjectState值和string值之间的转换。当将值从ProjectState enum移动到Projects表时，将使用该ToString()函数转换值。换另一种方式时，表中string的值将被解析为一个enum值。始终使用相同的方案在数据库列中的enum值和string值之间进行转换。

ProjectStateDescriptionConfiguration类如下所示。

ProjectStateDescriptionConfiguration.cs：

1.  
   using System;
2.  
   using Microsoft.EntityFrameworkCore;
3.  
   using Microsoft.EntityFrameworkCore.Metadata.Builders;
4.  
   using QuantumWeb.Model;
5.  
    
6.  
   namespace QuantumWeb.Data
7.  
   {
8.  
   /// <summary>
9.  
   /// ProjectState Description Configuration Class
10.  
    /// </summary>
11.  
    public class ProjectStateDescriptionConfiguration :
12.  
    IEntityTypeConfiguration<ProjectStateDescription>
13.  
    {
14.  
     
15.  
    public void Configure(EntityTypeBuilder<ProjectStateDescription> builder)
16.  
    {
17.  
    builder.ToTable("ProjectStateDescriptions");
18.  
    builder.HasKey(p => p.ProjectStateCode);
19.  
    builder.Property(p => p.ProjectStateCode)
20.  
    .HasColumnType("nvarchar(15)")
21.  
    .HasConversion(
22.  
    p => p.ToString(),
23.  
    p => (ProjectState)Enum.Parse(typeof(ProjectState), p));
24.  
    builder.Property(p => p.StateDescription)
25.  
    .IsRequired()
26.  
    .HasColumnType("nvarchar(80)")
27.  
    .HasMaxLength(80);
28.  
    } // end public void Configure(EntityTypeBuilder<ProjectStateDescription> builder)
29.  
     
30.  
    } // end public class ProjectStateDescriptionConfiguration :
31.  
    // IEntityTypeConfiguration<ProjectStateDescription>
32.  
     
33.  
    } // end namespace QuantumWeb.Data

现在，我们更新QuantumDbContext类。

然后更新QuantumDbContext.cs：

1.  
   using Microsoft.EntityFrameworkCore;
2.  
   using QuantumWeb.Model;
3.  
    
4.  
   namespace QuantumWeb.Data
5.  
   {
6.  
   public class QuantumDbContext : DbContext
7.  
   {
8.  
   public QuantumDbContext (DbContextOptions<QuantumDbContext> options)
9.  
   : base(options)
10.  
    {
11.  
    } // end public QuantumDbContext (DbContextOptions<QuantumDbContext> options)
12.  
     
13.  
    #region DbSets
14.  
     
15.  
    /// <summary>
16.  
    /// Customer DbSet
17.  
    /// </summary>
18.  
    public DbSet<Customer> Customers { get; set; }
19.  
     
20.  
    /// <summary>
21.  
    /// Project DbSet
22.  
    /// </summary>
23.  
    public DbSet<Project> Projects { get; set; }
24.  
     
25.  
    /// <summary>
26.  
    /// ProjectStateDescription DbSet
27.  
    /// </summary>
28.  
    public DbSet<ProjectStateDescription> ProjectStateDescriptions { get; set; }
29.  
     
30.  
    #endregion // DbSets
31.  
     
32.  
    /// <summary>
33.  
    /// Data Model Creation Method
34.  
    /// </summary>
35.  
    /// <param name="modelBuilder">ModelBuilder instance</param>
36.  
    protected override void OnModelCreating(ModelBuilder modelBuilder)
37.  
    {
38.  
    modelBuilder.ApplyConfiguration(new CustomerConfiguration());
39.  
    modelBuilder.ApplyConfiguration(new ProjectConfiguration());
40.  
    modelBuilder.ApplyConfiguration(new ProjectStateDescriptionConfiguration());
41.  
    } // end protected override void OnModelCreating(ModelBuilder modelBuilder)
42.  
     
43.  
    } // end public class QuantumDbContext : DbContext
44.  
     
45.  
    } // end namespace QuantumWeb.Data

现在为Project和ProjectState实体添加EF迁移。(译者注：同样需要调整appsettings.json中数据库连接字符串，建议删除Migrations文件夹后在执行下面的命令，同时提醒，在执行下面命令后需要命令update-database更新到数据库)

Add-Migration Added-Project-ProjectState

生成 ~\Migrations\20181021203503_Added-Project-ProjectState.cs:

1.  
   using Microsoft.EntityFrameworkCore.Metadata;
2.  
   using Microsoft.EntityFrameworkCore.Migrations;
3.  
    
4.  
   namespace QuantumWeb.Migrations
5.  
   {
6.  
   public partial class AddedProjectProjectState : Migration
7.  
   {
8.  
   protected override void Up(MigrationBuilder migrationBuilder)
9.  
   {
10.  
    migrationBuilder.CreateTable(
11.  
    name: "ProjectStateDescriptions",
12.  
    columns: table => new
13.  
    {
14.  
    ProjectStateCode =
15.  
    table.Column<string>(type: "nvarchar(15)", nullable: false),
16.  
    StateDescription =
17.  
    table.Column<string>(type: "nvarchar(80)", maxLength: 80, nullable: false)
18.  
    },
19.  
    constraints: table =>
20.  
    {
21.  
    table.PrimaryKey("PK_ProjectStateDescriptions", x => x.ProjectStateCode);
22.  
    });
23.  
     
24.  
    migrationBuilder.CreateTable(
25.  
    name: "Projects",
26.  
    columns: table => new
27.  
    {
28.  
    ProjectId = table.Column<int>(type: "int", nullable: false)
29.  
    .Annotation("SqlServer:ValueGenerationStrategy",
30.  
    SqlServerValueGenerationStrategy.IdentityColumn),
31.  
    ProjectName = table.Column<string>(type: "nvarchar(80)",
32.  
    maxLength: 80, nullable: false),
33.  
    CustomerId = table.Column<int>(type: "int", nullable: false),
34.  
    ProjectStateCode = table.Column<string>
35.  
    (type: "nvarchar(15)", nullable: false, defaultValue: "Prospect")
36.  
    },
37.  
    constraints: table =>
38.  
    {
39.  
    table.PrimaryKey("PK_Projects", x => x.ProjectId);
40.  
    table.ForeignKey(
41.  
    name: "FK_Projects_Customers_CustomerId",
42.  
    column: x => x.CustomerId,
43.  
    principalTable: "Customers",
44.  
    principalColumn: "CustomerId",
45.  
    onDelete: ReferentialAction.Cascade);
46.  
    table.ForeignKey(
47.  
    name: "FK_Projects_ProjectStateDescriptions_ProjectStateCode",
48.  
    column: x => x.ProjectStateCode,
49.  
    principalTable: "ProjectStateDescriptions",
50.  
    principalColumn: "ProjectStateCode",
51.  
    onDelete: ReferentialAction.Cascade);
52.  
    });
53.  
     
54.  
    migrationBuilder.CreateIndex(
55.  
    name: "IX_Projects_CustomerId",
56.  
    table: "Projects",
57.  
    column: "CustomerId");
58.  
     
59.  
    migrationBuilder.CreateIndex(
60.  
    name: "IX_Projects_ProjectStateCode",
61.  
    table: "Projects",
62.  
    column: "ProjectStateCode");
63.  
    }
64.  
     
65.  
    protected override void Down(MigrationBuilder migrationBuilder)
66.  
    {
67.  
    migrationBuilder.DropTable(
68.  
    name: "Projects");
69.  
     
70.  
    migrationBuilder.DropTable(
71.  
    name: "ProjectStateDescriptions");
72.  
    }
73.  
    }
74.  
    }

在Update- Database命令之后，SQL Server Management Studio（SSMS）中的数据库关系图如下所示。

使用Customer- Project- ProjectState表的QuantumDbContext数据库关系图：

修改Project和ProjectState的Razor 页。

我们需要为项目的应用程序添加一些自定义客户Razor 页面。首先，我们需要为CustomerProjects添加一个指向Customer/Index页面的链接。

添加CustomerProjects 链接指向Pages\Customers\Index.cshtml:

1.  
   @page
2.  
   @model QuantumWeb.Pages.Customers.IndexModel
3.  
    
4.  
   @{
5.  
   ViewData["Title"] = "Index";
6.  
   }
7.  
    
8.  
   <h2>Index</h2>
9.  
    
10.  
    <p>
11.  
    <a asp-page="Create">Create New</a>
12.  
    <!-- A link to the Pages/Customers/Create page to create a new Customer -->
13.  
    </p>
14.  
    <!-- An HTML table to display existing Customers -->
15.  
    <table class="table">
16.  
    <thead>
17.  
    <tr>
18.  
    <th>
19.  
    @Html.DisplayNameFor(model => model.Customer[0].CustomerName)
20.  
    </th>
21.  
    <th>
22.  
    @Html.DisplayNameFor(model => model.Customer[0].CustomerContact)
23.  
    </th>
24.  
    <th>
25.  
    @Html.DisplayNameFor(model => model.Customer[0].CustomerPhone)
26.  
    </th>
27.  
    <th>
28.  
    @Html.DisplayNameFor(model => model.Customer[0].CustomerEmail)
29.  
    </th>
30.  
    <th></th>
31.  
    </tr>
32.  
    </thead>
33.  
    <tbody>
34.  
    @foreach (var item in Model.Customer) {
35.  
    <tr>
36.  
    <td>
37.  
    @Html.DisplayFor(modelItem => item.CustomerName)
38.  
    </td>
39.  
    <td>
40.  
    @Html.DisplayFor(modelItem => item.CustomerContact)
41.  
    </td>
42.  
    <td>
43.  
    @Html.DisplayFor(modelItem => item.CustomerPhone)
44.  
    </td>
45.  
    <td>
46.  
    @Html.DisplayFor(modelItem => item.CustomerEmail)
47.  
    </td>
48.  
    <td>
49.  
    <a asp-page="./Edit" asp-route-id="@item.CustomerId">Edit</a> |
50.  
    <!-- A link to the Pages/Customers/Edit page to edit an existing Customer -->
51.  
    <a asp-page="./Details" asp-route-id="@item.CustomerId">Details</a> |
52.  
    <!--
53.  
    A link to the Pages/Customers/Details page to display the details for an existing
54.  
    Customer
55.  
    -->
56.  
    <a asp-page="./CustomerProjects" asp-route-id="@item.CustomerId">Projects</a> |
57.  
    <!--
58.  
    A link to the Pages/Customers/CustomerProjects page to display & manage the
59.  
    Projects for an existing Customer
60.  
    -->
61.  
    <a asp-page="./Delete" asp-route-id="@item.CustomerId">Delete</a>
62.  
    <!-- A link to the Pages/Customers/Delete page to delete an existing Customer -->
63.  
    </td>
64.  
    </tr>
65.  
    }
66.  
    </tbody>
67.  
    </table>

我们将如下构建几个自定义Customers Razor页面。

为客户设计的定制构建Razor页面：

搭建Customers/CustomerProjects Razor 页面：

单击“ 添加 ”将为CustomerProjects Index页面生成shell文件。

生成~Pages\Customers\CustomerProjects.cshtml

1.  
   @page
2.  
   @model QuantumWeb.Pages.Customers.CustomerProjectsModel
3.  
   @{
4.  
   ViewData["Title"] = "CustomerProjects";
5.  
   }
6.  
    
7.  
   <h2>CustomerProjects</h2>

生成~Pages\Customers\CustomerProjects.cshtml.cs

1.  
   using System;
2.  
   using System.Collections.Generic;
3.  
   using System.Linq;
4.  
   using System.Threading.Tasks;
5.  
   using Microsoft.AspNetCore.Mvc;
6.  
   using Microsoft.AspNetCore.Mvc.RazorPages;
7.  
    
8.  
   namespace QuantumWeb.Pages.Customers
9.  
   {
10.  
    public class CustomerProjectsModel : PageModel
11.  
    {
12.  
    public void OnGet()
13.  
    {
14.  
     
15.  
    }
16.  
    }
17.  
    }

我们将在每种情况下修改这些shell文件以满足我们的需求。CustomerProjects Index 页面的修改文件。

修改了~Pages\Customers\CustomerProjects.cshtml

1.  
   @page "{id:int?}"
2.  
   @model QuantumWeb.Pages.Customers.CustomerProjectsModel
3.  
   @{
4.  
   ViewData["Title"] = "Customer Projects";
5.  
   }
6.  
    
7.  
   <h2>Customer Projects</h2>
8.  
    
9.  
   <div>
10.  
    <h4>Customer</h4>
11.  
    <hr />
12.  
    <dl class="dl-horizontal">
13.  
    <dt>
14.  
    @Html.DisplayNameFor(model => model.Customer.CustomerId)
15.  
    </dt>
16.  
    <dd>
17.  
    @Html.DisplayFor(model => model.Customer.CustomerId)
18.  
    </dd>
19.  
    <dt>
20.  
    @Html.DisplayNameFor(model => model.Customer.CustomerName)
21.  
    </dt>
22.  
    <dd>
23.  
    @Html.DisplayFor(model => model.Customer.CustomerName)
24.  
    </dd>
25.  
    <dt>
26.  
    @Html.DisplayNameFor(model => model.Customer.Projects)
27.  
    </dt>
28.  
    <dd>
29.  
    <table class="table">
30.  
    <tr>
31.  
    <th>Project ID</th>
32.  
    <th>Project Name</th>
33.  
    <th>Project State</th>
34.  
    <th></th>
35.  
    </tr>
36.  
    @foreach (var item in Model.Customer.Projects)
37.  
    {
38.  
    <tr>
39.  
    <td>
40.  
    @Html.DisplayFor(modelItem => item.ProjectId)
41.  
    </td>
42.  
    <td>
43.  
    @Html.DisplayFor(modelItem => item.ProjectName)
44.  
    </td>
45.  
    <td>
46.  
    @Html.DisplayFor(modelItem => item.ProjectStateCode)
47.  
    </td>
48.  
    <td>
49.  
    <a asp-page="./CustomerProjectEdit"
50.  
     
51.  
    asp-route-id="@item.ProjectId">Edit</a> |
52.  
    <a asp-page="./CustomerProjectDelete"
53.  
     
54.  
    asp-route-id="@item.ProjectId">Delete</a>
55.  
    </td>
56.  
    </tr>
57.  
    }
58.  
    </table>
59.  
    </dd>
60.  
    </dl>
61.  
    </div>
62.  
     
63.  
    <div>
64.  
    <a asp-page="CustomerProjectCreate" asp-route-id="@Model.Customer.CustomerId">
65.  
    Create New Project</a> |
66.  
    <a asp-page="./Index">Back to List</a>
67.  
    </div>

“ {id:int?}”表示需要整数参数，id需要或者请求页面将返回HTTP 401（未找到页面）错误。在这种情况下，这是目标Customer的标识符（CustomerId）。另外，请注意引用该CustomerProjectCreate页面的链接。

<a asp-page="CustomerProjectCreate" asp-route-id="@Model.Customer.CustomerId">Create New Project</a> |

这将把我们带到CustomerProjectCreate尚未创建的页面，为引用Customer创建一个新的Project。

修改了~Pages\Customers\CustomerProjects.cshtml.cs

1.  
   using System.Threading.Tasks;
2.  
   using Microsoft.AspNetCore.Mvc;
3.  
   using Microsoft.AspNetCore.Mvc.RazorPages;
4.  
   using Microsoft.EntityFrameworkCore;
5.  
   using QuantumWeb.Data;
6.  
   using QuantumWeb.Model;
7.  
    
8.  
   namespace QuantumWeb.Pages.Customers
9.  
   {
10.  
    public class CustomerProjectsModel : PageModel
11.  
    {
12.  
    private readonly QuantumDbContext _context;
13.  
     
14.  
    public CustomerProjectsModel(QuantumDbContext context)
15.  
    {
16.  
    _context = context;
17.  
    } // end public CustomerProjectsModel(QuantumDbContext context)
18.  
     
19.  
    public Customer Customer { get; set; }
20.  
     
21.  
    public async Task<IActionResult> OnGet(int? id)
22.  
    {
23.  
    if (id == null)
24.  
    {
25.  
    return NotFound();
26.  
    } // endif (id == null)
27.  
     
28.  
    Customer = await _context.Customers
29.  
    .Include(c => c.Projects)
30.  
    .FirstOrDefaultAsync(c => c.CustomerId == id);
31.  
     
32.  
    if (Customer == null)
33.  
    {
34.  
    return NotFound();
35.  
    } // endif (Customer == null)
36.  
     
37.  
    return Page();
38.  
    } // end public async Task<IActionResult> OnGet(int? id)
39.  
     
40.  
    } // end public class CustomerProjectsModel : PageModel
41.  
     
42.  
    } // end namespace QuantumWeb.Pages.Customers

请注意，OnGet处理程序具有可为空的整数参数，id应该是如上所述的CustomerId。

QuantumWeb 应用客户页面： https//localhost: 44306/Customers 具有项目链接。

Customer Projects页面：https//localhost: 44306/Customers/CustomerProjects/1（无项目）

“ 创建新项目 ”链接将激活自定义CustomerProjectCreate Razor页面。我们现在搭建这个页面。

搭建Customers/CustomerProjectCreate Razor页面：

Initial~Pages\Customers\CustomerProjectCreate.cshtml.cs

1.  
   using System.Threading.Tasks;
2.  
   using Microsoft.AspNetCore.Mvc;
3.  
   using Microsoft.AspNetCore.Mvc.RazorPages;
4.  
   using Microsoft.AspNetCore.Mvc.Rendering;
5.  
   using Microsoft.EntityFrameworkCore;
6.  
   using QuantumWeb.Data;
7.  
   using QuantumWeb.Model;
8.  
    
9.  
   namespace QuantumWeb.Pages.Customers
10.  
    {
11.  
    public class CustomerProjectCreateModel : PageModel
12.  
    {
13.  
    private readonly QuantumDbContext _context;
14.  
     
15.  
    public CustomerProjectCreateModel(QuantumDbContext context)
16.  
    {
17.  
    _context = context;
18.  
    } // end public CustomerProjectCreateModel(QuantumContext context)
19.  
     
20.  
    [BindProperty]
21.  
    public Customer Customer { get; set; }
22.  
     
23.  
    public async Task<IActionResult> OnGet(int? id)
24.  
    {
25.  
    if (id == null)
26.  
    {
27.  
    return NotFound();
28.  
    } // endif (id == null)
29.  
     
30.  
    Customer = await _context.Customers
31.  
    .Include(c => c.Projects)
32.  
    .FirstOrDefaultAsync(c => c.CustomerId == id);
33.  
     
34.  
    if (Customer == null)
35.  
    {
36.  
    return NotFound();
37.  
    } // endif (Customer == null)
38.  
     
39.  
    ViewData["ProjectStateCode"] = new SelectList(_context.ProjectStateDescriptions,
40.  
    "ProjectStateCode", "StateDescription", ProjectState.Prospect);
41.  
     
42.  
    return Page();
43.  
     
44.  
    } // end public async Task<IActionResult> OnGet(int? id)
45.  
     
46.  
    [BindProperty]
47.  
    public Project Project { get; set; }
48.  
     
49.  
    public async Task<IActionResult> OnPostAsync()
50.  
    {
51.  
    if (!ModelState.IsValid)
52.  
    {
53.  
    return Page();
54.  
    } // endif (!ModelState.IsValid)
55.  
     
56.  
    Project.CustomerId = Customer.CustomerId;
57.  
     
58.  
    _context.Projects.Add(Project);
59.  
    await _context.SaveChangesAsync();
60.  
     
61.  
    return RedirectToPage("./CustomerProjects", new { id = Customer.CustomerId });
62.  
    } // end public async Task<IActionResult> OnPostAsync()
63.  
     
64.  
    } // end public class CustomerProjectCreateModel : PageModel
65.  
     
66.  
    } // end namespace QuantumWeb.Pages.Customers

请注意此代码中的这些行。 

1.  
   [BindProperty]
2.  
   public Customer Customer { get; set; }

该[BindProperty]将Customer实例绑定到UI的元素，以便在浏览器和Web服务器之间保留它们的值。另请注意，此属性也适用于Project实例。

1.  
   Customer = await _context.Customers
2.  
   .Include(c => c.Projects)
3.  
   .FirstOrDefaultAsync(c => c.CustomerId == id);

此语句对数据库执行查询，以检索Customer其主键值CustomerId与输入参数id值及其关联Project记录匹配的记录。如果有，该.Include函数的功能是查询中包含相关记录。

1.  
   ViewData["ProjectStateCode"] = new SelectList(_context.ProjectStateDescriptions,
2.  
   "ProjectStateCode", "StateDescription", ProjectState.Prospect);

ViewData是一个无类型的键值字典，用于在CustomerProjectCreateModel类（在.cshtml.cs文件中）和.cshtml文件中的HTML 之间传递值。这类似于MVC中将数据从Controller 传递到View，在使用ViewData中，数据仅在HTTP请求中持久存在。其成员由ProjectStateDescriptions数据库表中的查询填充。在这种情况下，_context.ProjectStateDescriptions是IEnumerable<ProjectStateDescription>从查询返回的。ProjectStateCode是表中的主键，表示ViewData字典中的键。StateDescription成为ViewData字典中的关联值。ViewData将用来填充在CustomerProjectCreate.cshtml（见下文）中的<select>元素。ProjectState.Prospect是为<select>从ProjectState enum中默认选择的值。您可以阅读更多ViewData信息在以下链接上 https：//www.tektutorialshub.com/viewbag-viewdata-asp-net-core/。（译者注：需要在ProjectStateDescriptions数据库表中手动加入数据，具体可见下图展示的数据加，ProjectStateCode字段的值就是对应枚举中的值--定义在代码中的名称。如此值为Completed，StateDescription字段值为project is complete，以此类推）

初始化~Pages\ Customers\CustomerProjectCreate.cshtml：

1.  
   @page
2.  
   @model QuantumWeb.Pages.Customers.CustomerProjectCreateModel
3.  
   @{
4.  
   ViewData["Title"] = "Create Customer Project";
5.  
   }
6.  
    
7.  
   <h2>Create Customer Project</h2>
8.  
   <hr />
9.  
   <dl class="dl-horizontal">
10.  
    <dt>
11.  
    @Html.DisplayNameFor(model => model.Customer.CustomerId)
12.  
    </dt>
13.  
    <dd>
14.  
    @Html.DisplayFor(model => model.Customer.CustomerId)
15.  
    </dd>
16.  
    <dt>
17.  
    @Html.DisplayNameFor(model => model.Customer.CustomerName)
18.  
    </dt>
19.  
    <dd>
20.  
    @Html.DisplayFor(model => model.Customer.CustomerName)
21.  
    </dd>
22.  
    </dl>
23.  
    <div class="row">
24.  
    <div class="col-md-4">
25.  
    <form method="post">
26.  
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>
27.  
    <input type="hidden" asp-for="Customer.CustomerId" />
28.  
    <div class="form-group">
29.  
    <label asp-for="Project.ProjectName" class="control-label"></label>
30.  
    <input asp-for="Project.ProjectName" class="form-control">
31.  
    </div>
32.  
    <div class="form-group">
33.  
    <label asp-for="Project.ProjectStateCode" class="control-label"></label>
34.  
    <select asp-for="Project.ProjectStateCode" class="form-control"
35.  
     
36.  
    asp-items="ViewBag.ProjectStateCode">
37.  
    </select>
38.  
    </div>
39.  
    <div class="form-group">
40.  
    <input type="submit" value="Create" class="btn btn-default" />
41.  
    </div>
42.  
    </form>
43.  
    </div>
44.  
    </div>
45.  
     
46.  
    <div>
47.  
    <a asp-page="CustomerProjects" asp-route-id="@Model.Customer.CustomerId">
48.  
    Back to Customer Projects
49.  
    </a>
50.  
    </div>
51.  
     
52.  
    @section Scripts {
53.  
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
54.  
    }

关键要素如下：

<input type="hidden" asp-for="Customer.CustomerId" />

这个隐藏<input>捕获目标CustomerId以便在<form>发布时可用它来创建Project。

1.  
   <select asp-for="Project.ProjectStateCode" class="form-control"
2.  
   asp-items="ViewBag.ProjectStateCode">
3.  
   </select>

此<select>元素将显示为UI中的下拉列表，其中包含CustomerProjectCreate.OnGet()方法中ViewData填充的值。

初始化 ~Pages\Customers\CustomerProjectCreate.cshtml：

这将显示最初显示的Customers/CustomerProjectCreate页面。

CustomerProjectCreate 包含数据的页面：

点击“ Create”后，我们会看到：

客户Projects页面添加Project：

接下来的两个图显示了为两个Customers添加其他Projects之后的情况。

客户项目页面包含Mirarex Oil＆Gas的2个项目：

客户项目页面包含Polyolefin Processing, Inc.的3个项目

我们现在可以添加另一个页面来编辑Customer项目，CustomerProjectEdit页面。

搭建 Customers/CustomerProjectEdit Razor Page

初始化~Pages\Customers\CustomerProjectEdit.cshtml.cs

1.  
   using System.Threading.Tasks;
2.  
   using Microsoft.AspNetCore.Mvc;
3.  
   using Microsoft.AspNetCore.Mvc.RazorPages;
4.  
   using Microsoft.AspNetCore.Mvc.Rendering;
5.  
   using Microsoft.EntityFrameworkCore;
6.  
   using QuantumWeb.Data;
7.  
   using QuantumWeb.Model;
8.  
    
9.  
   namespace QuantumApp.Pages.Customers
10.  
    {
11.  
    public class CustomerProjectEditModel : PageModel
12.  
    {
13.  
    private readonly QuantumDbContext _context;
14.  
     
15.  
    public CustomerProjectEditModel(QuantumDbContext context)
16.  
    {
17.  
    _context = context;
18.  
    } // end public CustomerProjectEditModel(QuantumDbContext context)
19.  
     
20.  
    [BindProperty]
21.  
    public Customer Customer { get; set; }
22.  
    [BindProperty]
23.  
    public Project Project { get; set; }
24.  
     
25.  
    public async Task<IActionResult> OnGet(int? id)
26.  
    {
27.  
    if (id == null)
28.  
    {
29.  
    return NotFound();
30.  
    } // endif (id == null)
31.  
     
32.  
    Project = await _context.Projects
33.  
    .Include(p => p.Customer)
34.  
    .FirstOrDefaultAsync(p => p.ProjectId == id);
35.  
     
36.  
    if (Project == null)
37.  
    {
38.  
    return NotFound();
39.  
    } // endif (Project == null)
40.  
     
41.  
    Customer = Project.Customer;
42.  
     
43.  
    ViewData["ProjectStateCode"] = new SelectList(_context.ProjectStateDescriptions,
44.  
    "ProjectStateCode", "StateDescription", ProjectState.Prospect);
45.  
     
46.  
    return Page();
47.  
    } // end public async Task<IActionResult> OnGet(int? id)
48.  
     
49.  
    public async Task<IActionResult> OnPostAsync(int? id)
50.  
    {
51.  
    if (!ModelState.IsValid)
52.  
    {
53.  
    return Page();
54.  
    } // endif (!ModelState.IsValid)
55.  
     
56.  
    var projectToUpdate = await _context.Projects.FindAsync(id);
57.  
     
58.  
    if (projectToUpdate == null)
59.  
    {
60.  
    return NotFound();
61.  
    } // endif (projectToUpdate == null)
62.  
     
63.  
    projectToUpdate.CustomerId = Customer.CustomerId;
64.  
     
65.  
    if (await TryUpdateModelAsync<Project>(
66.  
    projectToUpdate,
67.  
    "project",
68.  
    p => p.ProjectName, p => p.ProjectStateCode))
69.  
    {
70.  
    await _context.SaveChangesAsync();
71.  
    return RedirectToPage("./CustomerProjects", new { id = Customer.CustomerId });
72.  
    }
73.  
     
74.  
    return Page();
75.  
    } // end public async Task<IActionResult> OnPostAsync(int? id)
76.  
     
77.  
    } // end public class CustomerProjectEditModel : PageModel
78.  
     
79.  
    } // end namespace QuantumApp.Pages.Customers

此代码与CustomerProjectCreate页面在.Include和ViewData方面具有相同的构件。

初始化~Pages\Customers\CustomerProjectEdit.cshtml

1.  
   @page "{id:int?}"
2.  
   @model QuantumWeb.Pages.Customers.CustomerProjectEditModel
3.  
   @{
4.  
   ViewData["Title"] = "Edit Customer Project";
5.  
   }
6.  
    
7.  
   <h2>Edit Customer Project</h2>
8.  
   <hr />
9.  
   <dl class="dl-horizontal">
10.  
    <dt>
11.  
    @Html.DisplayNameFor(model => model.Customer.CustomerId)
12.  
    </dt>
13.  
    <dd>
14.  
    @Html.DisplayFor(model => model.Customer.CustomerId)
15.  
    </dd>
16.  
    <dt>
17.  
    @Html.DisplayNameFor(model => model.Customer.CustomerName)
18.  
    </dt>
19.  
    <dd>
20.  
    @Html.DisplayFor(model => model.Customer.CustomerName)
21.  
    </dd>
22.  
    </dl>
23.  
    <div class="row">
24.  
    <div class="col-md-4">
25.  
    <form method="post">
26.  
    <div asp-validation-summary="ModelOnly" class="text-danger"></div>
27.  
    <input type="hidden" asp-for="Customer.CustomerId" />
28.  
    <div class="form-group">
29.  
    <label asp-for="Project.ProjectName" class="control-label"></label>
30.  
    <input asp-for="Project.ProjectName" class="form-control">
31.  
    </div>
32.  
    <div class="form-group">
33.  
    <label asp-for="Project.ProjectStateCode" class="control-label"></label>
34.  
    <select asp-for="Project.ProjectStateCode" class="form-control"
35.  
     
36.  
    asp-items="ViewBag.ProjectStateCode">
37.  
    </select>
38.  
    </div>
39.  
    <div class="form-group">
40.  
    <input type="submit" value="Save" class="btn btn-default" />
41.  
    </div>
42.  
    </form>
43.  
    </div>
44.  
    </div>
45.  
     
46.  
    <div>
47.  
    <a asp-page="CustomerProjects" asp-route-id="@Model.Customer.CustomerId">
48.  
    Back to Customer Projects
49.  
    </a>
50.  
    </div>
51.  
     
52.  
    @section Scripts {
53.  
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
54.  
    }

关于CustomerId的隐藏<input>和<select>，此页面具有与CustomerProjectCreate页面相同的元素。

Customer Projects 页面包含Mirarex Oil＆Gas的2个项目——用于编辑：

Mirarex Oil＆Gas, Zolar Pipeline的客户项目编辑页面：

客户项目页面包含Mirarex Oil & Gas 的2个项目——项目编辑：

通过CustomerProjectDelete页面，此项目的最后一个功能是删除。

搭建 Customers/CustomerProjectDelete Razor页面：

初始化~Pages\Customers\CustomerProjectDelete.cshtml.cs

1.  
   using System.Threading.Tasks;
2.  
   using Microsoft.AspNetCore.Mvc;
3.  
   using Microsoft.AspNetCore.Mvc.RazorPages;
4.  
   using Microsoft.EntityFrameworkCore;
5.  
   using QuantumWeb.Data;
6.  
   using QuantumWeb.Model;
7.  
    
8.  
   namespace QuantumWeb.Pages.Customers
9.  
   {
10.  
    public class CustomerProjectDeleteModel : PageModel
11.  
    {
12.  
    private readonly QuantumDbContext _context;
13.  
     
14.  
    public CustomerProjectDeleteModel(QuantumDbContext context)
15.  
    {
16.  
    _context = context;
17.  
    } // end public CustomerProjectDeleteModel(QuantumContext context)
18.  
     
19.  
    [BindProperty]
20.  
    public Customer Customer { get; set; }
21.  
    [BindProperty]
22.  
    public Project Project { get; set; }
23.  
     
24.  
    public async Task<IActionResult> OnGetAsync(int? id)
25.  
    {
26.  
    if (id == null)
27.  
    {
28.  
    return NotFound();
29.  
    } // endif (id == null)
30.  
     
31.  
    Project = await _context.Projects
32.  
    .Include(p => p.Customer)
33.  
    .FirstOrDefaultAsync(p => p.ProjectId == id);
34.  
     
35.  
    if (Project == null)
36.  
    {
37.  
    return NotFound();
38.  
    } // endif (Project == null)
39.  
     
40.  
    Customer = Project.Customer;
41.  
     
42.  
    return Page();
43.  
    } // end public async Task<IActionResult> OnGet(int? id)
44.  
     
45.  
    public async Task<IActionResult> OnPostAsync(int? id)
46.  
    {
47.  
    if (id == null)
48.  
    {
49.  
    return NotFound();
50.  
    } // endif (id == null)
51.  
     
52.  
    Project = await _context.Projects
53.  
    .Include(p => p.Customer)
54.  
    .FirstOrDefaultAsync(p => p.ProjectId == id);
55.  
     
56.  
    if (Project != null)
57.  
    {
58.  
    _context.Projects.Remove(Project);
59.  
    await _context.SaveChangesAsync();
60.  
    } // endif (Project != null)
61.  
     
62.  
    return RedirectToPage("./CustomerProjects", new { id = Project.Customer.CustomerId });
63.  
    } // end public async Task<IActionResult> OnPostAsync(int? id)
64.  
     
65.  
    } // end public class CustomerProjectDeleteModel : PageModel
66.  
     
67.  
    } // end namespace QuantumWeb.Pages.Customer

初始化~Pages\Customers\CustomerProjectDelete.cshtml

1.  
   @page "{id:int?}"
2.  
   @model QuantumWeb.Pages.Customers.CustomerProjectDeleteModel
3.  
   @{
4.  
   ViewData["Title"] = "Delete Customer Project";
5.  
   }
6.  
    
7.  
   <h2>Delete Customer Project</h2>
8.  
    
9.  
   <h3>Are you sure you want to delete this?</h3>
10.  
    <div>
11.  
    <dl class="dl-horizontal">
12.  
    <dt>
13.  
    @Html.DisplayNameFor(model => model.Customer.CustomerName)
14.  
    </dt>
15.  
    <dd>
16.  
    @Html.DisplayFor(model => model.Customer.CustomerName)
17.  
    </dd>
18.  
    <dt>
19.  
    @Html.DisplayNameFor(model => model.Project.ProjectId)
20.  
    </dt>
21.  
    <dd>
22.  
    @Html.DisplayFor(model => model.Project.ProjectId)
23.  
    </dd>
24.  
    <dt>
25.  
    @Html.DisplayNameFor(model => model.Project.ProjectName)
26.  
    </dt>
27.  
    <dd>
28.  
    @Html.DisplayFor(model => model.Project.ProjectName)
29.  
    </dd>
30.  
    <dt>
31.  
    @Html.DisplayNameFor(model => model.Project.ProjectStateCode)
32.  
    </dt>
33.  
    <dd>
34.  
    @Html.DisplayFor(model => model.Project.ProjectStateCode)
35.  
    </dd>
36.  
    </dl>
37.  
     
38.  
    <form method="post">
39.  
    <input type="hidden" asp-for="Project.ProjectId" />
40.  
    <a asp-page="CustomerProjects" asp-route-id="@Model.Customer.CustomerId">
41.  
    Back to Customer Projects
42.  
    </a> |
43.  
    <input type="submit" value="Delete" class="btn btn-default" />
44.  
    </form>
45.  
    </div>

客户项目页面包含Mirarex Oil & Gas的3个项目：

删除客户项目页面——删除Ouachita Shale：

客户项目页面包含Mirarex Oil＆Gas的2个项目：

此时，我们可以总结下表中的测试数据：

Customers, Projects, ProjectStates

CustomerId	Customer Name	ProjectId	Project Name	ProjectStateCode	StateDescription
1	Mirarex Oil & Gas, LLC	1	Zolar Pipeline	UnderReview	Project is under review and negotiation
1	Mirarex Oil & Gas, LLC	2	Nelar Ranch Gas Fracturing	Prospect	Prospective or referred project
2	Polyolefin Processing, Inc.	3	Port Gibson Plant Expansion	Prospect	Prospective or referred project
2	Polyolefin Processing, Inc.	4	Jackson Plant Control System Upgrade	Prospect	Prospective or referred project
2	Polyolefin Processing, Inc.	5	Eutaw Plant Shutdown & Maintenance	Prospect	Prospective or referred project

下面可以进入第四部分进行学习。 

 https://blog.csdn.net/mzl87/article/details/85312583

原文地址：https://www.codeproject.com/Articles/1264330/ASP-NET-Core-Razor-Pages-Using-EntityFramework-C-2