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Asp核心,对象引用未设置为存储库模式中对象的实例

repository-pattern repository asp.net-core asp.net-mvc

topcool · 技术社区 · 6 年前

我正在开发asp core 1.1,我想创建一个 select 我的项目中的存储库模式。

存储库类中的我的代码:

public class AuthorReposetory : IDisposable
{
    private static ApplicationDbContext _context;

    public AuthorReposetory(ApplicationDbContext context)
    {
        _context = context;
    }




    public static List<Author> GetAuthorList()
    {
        List<Author> model = new List<Author>();

        model = _context.authors.Select(a => new Author
        {
            AuthorId = a.AuthorId,
            AuthorName = a.AuthorName,
            AuthorDescription = a.AuthorDescription
        }).ToList();

        return model;
    }

    public void Dispose()
    {
        throw new NotImplementedException();
    }

    ~AuthorReposetory()
    {
        Dispose();
    }
}

和在控制器中

[HttpGet]
public IActionResult Index()
{
    var q = AuthorReposetory.GetAuthorList();
    return View(q);
}

使现代化

这是我的创业课程

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
            .AddEnvironmentVariables();
        Configuration = builder.Build();
    }

    public IConfigurationRoot Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        //define Connection string
        services.AddDbContext<ApplicationDbContext>(option => option.UseSqlServer(Configuration.GetConnectionString("DefualtConnection")));
        //For Create and use identity in database
        services.AddIdentity<ApplicationUser, ApplicationRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();


        // Add framework services.
        services.AddMvc();
        services.AddAutoMapper();
        services.AddPaging();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole(Configuration.GetSection("Logging"));
        loggerFactory.AddDebug();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
            app.UseBrowserLink();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
        }

        app.UseStaticFiles();
        app.UseIdentity();


        app.UseMvc(routes =>
        {

            //New Area For Admin
            routes.MapRoute(
                name: "Admin",
                template: "{area:exists}/{controller=Admin}/{action=Index}/{id?}");

            //New Area For User
            routes.MapRoute(
                name: "UserProfile",
                template: "{area:exists}/{controller=UserProfile}/{action=Index}/{id?}");

            //tranditional Routing
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

appsettings中的我的连接字符串。json

{
  "ConnectionStrings": {
  "DefualtConnection" : "Data Source=.;Initial Catalog=DataBaseName;User ID = sa; Password = 123"
  },





  "Logging": {
   "IncludeScopes": false,
    "LogLevel": {
     "Default": "Warning"
    }
  }
}

问题是 Object reference not set to an instance of an object 运行时 model = _context.authors.Select(a => new Author 在存储库中。在上面,我展示了控制器代码、存储库类代码和启动代码。问题出在哪里?

注:控制器一切正常。问题就出在repository类中。

3 回复 | 直到 6 年前

Mike 6 年前

您使用的是静态方法,并且构造函数永远不会被调用,因为您永远不会创建对象。您必须将构造函数更改为:

public static AuthorReposetory()
{
    _context = new ApplicationDbContext(options => options.UseSqlServer(Configuration.GetConnectionString("DefualtConnection")));
}

但这是一种非常糟糕的做法,因为必须在构造函数中设置连接,这也会对上下文类产生硬依赖。

更好的解决方案是创建一个非静态类

public class AuthorRepository : IAuthorRepository
{
    private ApplicationDbContext _context;

    public AuthorRepository(ApplicationDbContext context)
    {
        _context = context;
    }

    // ...
}

public interface IAuthorRepository
{
    // ...
}

使用注入反转依赖关系:

启动。cs公司

public void ConfigureServices(IServiceCollection services)
{
    //define Connection string and setup dependency injection
    services.AddDbContext<ApplicationDbContext>(option => option.UseSqlServer(Configuration.GetConnectionString("DefualtConnection")));
    services.AddScoped<IAuthorRepository, AuthorRepository>();
    // ...
}

控制器:

public HomeController
{
    private IAuthorRepository _authorRepository;

    public HomeController(IAuthorRepository authorRepository)
    {
        _authorRepository = authorRepository;
    }

    [HttpGet]
    public IActionResult Index()
    {
        var q = _autorRepository.GetAuthorList();
        return View(q);
    }
}

Hix 6 年前

您的上下文对象可能为空。您的DI/IoC是如何配置的?我会这样调查的。

应按如下方式添加数据库上下文:

public void ConfigureServices(IServiceCollection服务) { 服务。AddDbContext(options=>options.UseSqlite(“数据源=blog.db”)); }

以下是有关如何配置db上下文的文档: https://docs.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

Ehsan Sajjad 6 年前

您尚未在中注册存储库类 services 因此,它无法通过容器解决。在您的 ConfigureServices 方法尝试以下操作:

services.AddScoped<AuthorReposetory>();