无法在 Blazor razor 页面（Blazor 服务器端）中注入 Controller、DbContext

Question

我正在使用最新的 .NET Core 技术栈包括：Microsoft Visual Studio Community 2019 Preview 版本 16.7.0 预览版 6.0 ； .NET Core 5.0.100-preview.7.20366.6； Microsoft.EntityFrameworkCore.SqlServer 版本 5.0.0-preview.7.20365.15 ；用于我的 Blazor 服务器端 Web 应用的 Microsoft SQLServer 2019。

在Startup.cs我有

services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
services.AddSingleton<SysAutoIdController>();

在文件SystemInformation.razor

@page "/system_information"
@using myproj.Forms
@using myproj.DTO
@using myproj.Models

@inject myproj.Data.ApplicationDbContext dbContext;
@inject myproj.Controllers.SysAutoIdController sysAutoIdController;


<h3>System information</h3>

database size = @foo

@code {
   string fooTemp = sysAutoIdController.getDbSize(dbContext);
   string foo = foo2.ToString();
}

控制器，文件SysAutoIdController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using myproj.Data;
using myproj.Models;
using Microsoft.EntityFrameworkCore;

namespace myproj.Controllers
{
    public class SysAutoIdController : Controller
    {
        ApplicationDbContext db = new ApplicationDbContext();

        public string getDbSize(ApplicationDbContext db2)
        {
            var foo = db2.SysautoId.FromSqlRaw("" +
        " SELECT a.dbdisk " +
        " FROM " +
            "(SELECT sys.databases.name AS dbname, " +
              "      CONVERT(VARCHAR, SUM(SIZE) * 8 / 1024) + \' MB\' AS dbdisk " +
            " FROM sys.databases " +
           " JOIN sys.master_files ON sys.databases.database_id = sys.master_files.database_id " +
           " GROUP BY sys.databases.name) a " +
        " WHERE a.dbname = \'mydatabase\' ");
            return foo.ToString();
        }
    }
}

错误

CS0236：字段初始化程序无法引用非静态字段， 方法或属性“SystemInformation.sysAutoIdController”

CS0236：字段初始值设定项无法引用非静态字段， 方法或属性“SystemInformation.dbContext”

如何在剃刀页面成功时运行sysAutoIdController.getDbSize(dbContext); 之类的内容？

Answer 1

“字段初始化程序”在对象的构造函数之前立即运行。对于 Blazor 页面，就在任何注入发生之前。 C# 语法不允许您使用尚未构造的实例中的任何内容。

@code {
   string fooTemp; // = sysAutoIdController.getDbSize(dbContext);
   string foo => foo2?.ToString();  // string.ToString() is a little pointless

    protected override async Task OnInitializedAsync()
    {
       // see if you can make getDbSize async, that would be better
       fooTemp = sysAutoIdController.getDbSize(dbContext);
    }
}

旁注：DbContext 是您需要管理的宝贵资源。让它注入Controller，你已经注册了所有东西：

public class SysAutoIdController : Controller
{
   public SysAutoIdController(ApplicationDbContext db)
   {
      _db = db;
   }

   ... 
}

    

Answer 2

感谢Henk Holtermanhttps://stackoverflow.com/a/63213132/3728901的回答

(1)控制器

using myproj.Data;

public class SysAutoIdController : Controller
{

   ApplicationDbContext _db;
    
   public SysAutoIdController(ApplicationDbContext db)
   {
      _db = db;
   }

   public string getDbSize()
        {
            var foo = _db.SysautoId.FromSqlRaw("" +
        " SELECT a.dbdisk " +
        " FROM " +
            "(SELECT sys.databases.name AS dbname, " +
              "      CONVERT(VARCHAR, SUM(SIZE) * 8 / 1024) + \' MB\' AS dbdisk " +
            " FROM sys.databases " +
           " JOIN sys.master_files ON sys.databases.database_id = sys.master_files.database_id " +
           " GROUP BY sys.databases.name) a " +
        " WHERE a.dbname = \'mydatabase\' ");
            return foo.ToString();
    }

}

（确实，原始SQL不起作用，我通过一个简单的查询尝试了，我稍后会修复它。）

(2) 我没有在Startup.cs中注入控制器

//services.AddSingleton<SysAutoIdController>(); // Important: must comment.

(3) 在剃刀文件中

@page "/system_information"
@using myproj.Forms
@using myproj.DTO
@using myproj.Models


@inject myproj.Data.ApplicationDbContext dbContext;
@*@inject myproj.Controllers.CommonController commonController;*@  @*must comment*@


Database size: @fooTemp

@code {
    string fooTemp;

    protected override async Task OnInitializedAsync()
    {
        myproj.Controllers.CommonController Cc = new Controllers.CommonController(dbContext);
        // see if you can make getDbSize async, that would be better
        fooTemp = Cc.getDbSize();
    }

}

然后就可以了！

真的，我不太了解这个问题，为什么它会起作用，有人可以发表评论或回答我更多信息。