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