[英]Access to DbContext with dependency injection
關於依賴注入的段落,我不明白官方文檔 。
他們說我可以使用一個控制器(但從這里我知道我不需要它因為我正在使用Razor頁面)或者我可以直接訪問ServiceProvider:
using (var context = serviceProvider.GetService<BloggingContext>())
{
// do stuff
}
但是如何在我項目的通用C#類中檢索對ServiceProvider的引用?
我在startup.cs中設置服務:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<MyDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("MyDbContext")));
services.AddHangfire(options => options.UseSqlServerStorage(Configuration.GetConnectionString("MyDbContext")));
services.AddOptions();
services.Configure<MySettings>(options => Configuration.GetSection("MySettings").Bind(options));
services.AddMvc().AddDataAnnotationsLocalization();
}
為了進一步澄清我的困惑,我想要做的是從Worker類添加/獲取數據。 在這里我找到了一個如何做到的例子:
using (var context = new BloggingContext())
{
var blog = new Blog { Url = "http://sample.com" };
context.Blogs.Add(blog);
context.SaveChanges();
Console.WriteLine(blog.BlogId + ": " + blog.Url);
}
但是如果我要使用依賴注入,我不能使用沒有參數DbContext的構造函數。 另一方面,如果我添加參數,我必須在調用構造函數時傳遞正確的值,如上例所示 - 這是最初的問題。
我將發布一個“完整”的例子。 我很難理解,但無論如何我都在努力:
Program.cs中
using Hangfire;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Options;
namespace MyProject
{
public class Program
{
public static void Main(string[] args)
{
IWebHost host = BuildWebHost(args);
BackgroundJob.Enqueue<MyClass>(x => x.ImportOperatorList());
host.Run();
}
public static IWebHost BuildWebHost(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.Build();
}
}
startup.cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Hangfire;
using MyProject.Models;
namespace MyProject
{
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.AddDbContext<MyProjectContext>(options => options.UseSqlServer(Configuration.GetConnectionString("MyProjectContext")));
services.AddHangfire(options => options.UseSqlServerStorage(Configuration.GetConnectionString("MyProjectContext")));
services.AddOptions();
services.Configure<MySettings>(options => Configuration.GetSection("MySettings").Bind(options));
services.AddMvc().AddDataAnnotationsLocalization();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
app.UseBrowserLink();
}
else
{
app.UseExceptionHandler("/Error");
}
app.UseStaticFiles();
app.UseHangfireDashboard();
app.UseHangfireServer();
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{controller}/{action=Index}/{id?}");
});
}
}
}
MyProjectContext.cs
using Microsoft.EntityFrameworkCore;
namespace MyProject.Models
{
public class MyProjectContext : DbContext
{
public MyProjectContext(DbContextOptions<MyProjectContext> options) : base(options) { }
public DbSet<Operator> Operators { get; set; }
}
public class Operator
{
public int Id { get; set; }
[MaxLength(40)]
public string Name { get; set; }
public int Password { get; set; }
}
}
MyClass.cs
using MyProject.Models;
using System;
using System.Diagnostics;
using System.IO;
using System.Text.RegularExpressions;
namespace MyProject
{
public class MyClass
{
const string REGEX_OPERATORS = "^(?<Id>.{4})(?<Name>.{40})(?<Password>.{5})";
private readonly Regex reOperators = new Regex(REGEX_OPERATORS, RegexOptions.Compiled);
public void ImportOperatorList()
{
var path = @"F:\testdata.txt";
string[] lines = File.ReadAllLines(path);
foreach (var line in lines)
{
Match match = reOperators.Match(line);
if (match.Success)
{
string rawId = match.Groups["Id"].Value;
string rawName = match.Groups["Name"].Value;
string rawPassword = match.Groups["Password"].Value;
int Id;
try
{
Id = int.Parse(rawId, System.Globalization.NumberStyles.Integer);
}
catch (Exception)
{
throw;
}
string Name = rawName;
int Password;
try
{
Password = int.Parse(rawPassword, System.Globalization.NumberStyles.Integer);
}
catch (Exception)
{
throw;
}
using (var context = new MyProjectContext(/* ??? */))
{
var op = new Operator
{
Id = Id,
Name = Name,
Password = Password
};
context.Operators.Add(op);
Debug.WriteLine(context.SaveChanges());
}
}
}
}
}
}
當然不完整也不可編譯,因為項目中有很多其他文件(即使沒有我自己的特定應用程序)。
建立自己的答案。
重構MyClass
依賴於抽象而不是與結核緊密耦合。
這是重構的MyClass
public class MyClass {
const string REGEX_OPERATORS = "^(?<Id>.{4})(?<Name>.{40})(?<Password>.{5})";
private readonly Regex reOperators = new Regex(REGEX_OPERATORS, RegexOptions.Compiled);
private readonly IFileSystem File;
private readonly IProjectContext context;
public MyClass(IFileSystem File, IProjectContext context) {
this.File = File;
this.context = context;
}
public void ImportOperatorList() {
var path = @"F:\testdata.txt";
var lines = File.ReadAllLines(path);
foreach (var line in lines) {
var match = reOperators.Match(line);
if (match.Success) {
string rawId = match.Groups["Id"].Value;
string rawName = match.Groups["Name"].Value;
string rawPassword = match.Groups["Password"].Value;
var op = new Operator {
Id = int.Parse(rawId, System.Globalization.NumberStyles.Integer),
Name = rawName,
Password = int.Parse(rawPassword, System.Globalization.NumberStyles.Integer)
};
context.Operators.Add(op);
}
}
if (lines.Length > 0)
Debug.WriteLine(context.SaveChanges());
}
}
通過以下修改
public interface IFileSystem {
string[] ReadAllLines(string path);
}
public class FileWrapper : IFileSystem {
public string[] ReadAllLines(string path) {
var lines = File.ReadAllLines(path);
return lines;
}
}
public interface IProjectContext : IDisposable {
DbSet<Operator> Operators { get; set; }
int SaveChanges();
//...add other functionality that needs to be exposed as needed
//eg: Database Database { get; }
//...
}
public class MyProjectContext : DbContext, IProjectContext {
public MyProjectContext(DbContextOptions<MyProjectContext> options) : base(options) { }
public DbSet<Operator> Operators { get; set; }
}
您將確保所有抽象都在組合根處注冊到服務容器。
public void ConfigureServices(IServiceCollection services) {
services.AddDbContext<MyProjectContext>(options => options.UseSqlServer(Configuration.GetConnectionString("MyProjectContext")));
services.AddHangfire(options => options.UseSqlServerStorage(Configuration.GetConnectionString("MyProjectContext")));
services.AddOptions();
services.Configure<MySettings>(options => Configuration.GetSection("MySettings").Bind(options));
services.AddMvc().AddDataAnnotationsLocalization();
//...adding additional services
services.AddScoped<IProjectContext, MyProjectContext>();
services.AddTransient<IFileSystem, FileWrapper>();
services.AddTransient<MyClass, MyClass>();
}
現在,當使用作用域服務提供程序時,您可以請求您的類,並在解析MyClass
時注入所有依賴項
using (var scope = host.Services.CreateScope()) {
var services = scope.ServiceProvider;
var myClass = services.GetRequiredService<MyClass>();
myClass.ImportOperatorList();
}
由於上面是作用域,容器將管理容器超出范圍時創建的任何服務的處置。
您必須手動將context參數傳遞給函數,依賴注入不會為您執行此操作。 因此,在program.cs中你可以添加:
using (var scope = host.Services.CreateScope())
{
var services = scope.ServiceProvider;
var context = services.GetRequiredService<MyProjectContext>();
// pass context to relevant Classes/Functions, i.e.
MyClass myClass = new MyClass();
myClass.ImportOperatorList(context);
}
在MyClass.cs中,您現在可以直接使用該變量:
public void ImportOperatorList(MyProjectContext context)
{
// ...
context.Operators.Add(op);
context.SaveChanges();
}
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