ASP.NET Core 2 无法解析 Microsoft EntityFrameworkCore DbContext 类型的服务 [英] ASP.NET Core 2 Unable to resolve service for type Microsoft EntityFrameworkCore DbContext

问题描述

当我运行我的 asp.net core 2 项目时，我收到以下错误消息:

When I run my asp.net core 2 projects I get the following error message:

InvalidOperationException:尝试激活ContosoUniversity.Service.Class.StudentService"时无法解析Microsoft.EntityFrameworkCore.DbContext"类型的服务.

InvalidOperationException: Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContext' while attempting to activate 'ContosoUniversity.Service.Class.StudentService'.

这是我的项目结构:

-- solution 'ContosoUniversity'
----- ContosoUniversity
----- ContosoUniversity.Model
----- ContosoUniversity.Service

IEntityService(相关代码):

public interface IEntityService<T> : IService
 where T : BaseEntity
{
    Task<List<T>> GetAllAsync();      
}

IEntityService(相关代码):

public abstract class EntityService<T> : IEntityService<T> where T : BaseEntity
{
    protected DbContext _context;
    protected DbSet<T> _dbset;

    public EntityService(DbContext context)
    {
        _context = context;
        _dbset = _context.Set<T>();
    }

    public async virtual Task<List<T>> GetAllAsync()
    {
        return await _dbset.ToListAsync<T>();
    }
}

实体:

public abstract class BaseEntity { 

}

public abstract class Entity<T> : BaseEntity, IEntity<T> 
{
    public virtual T Id { get; set; }
}

学生服务:

public interface IStudentService : IEntityService<Student>
{
    Task<Student> GetById(int Id);
}

学生服务:

public class StudentService : EntityService<Student>, IStudentService
{
    DbContext _context;

    public StudentService(DbContext context)
        : base(context)
    {
        _context = context;
        _dbset = _context.Set<Student>();
    }

    public async Task<Student> GetById(int Id)
    {
        return await _dbset.FirstOrDefaultAsync(x => x.Id == Id);
    }
}

学校环境:

public class SchoolContext : DbContext
{
    public SchoolContext(DbContextOptions<SchoolContext> options) : base(options)
    {
    }

    public DbSet<Course> Courses { get; set; }
    public DbSet<Enrollment> Enrollments { get; set; }
    public DbSet<Student> Students { get; set; }
}

最后是我的 Startup.cs 类:

public class Startup
{
    public Startup(IConfiguration configuration, IHostingEnvironment env, IServiceProvider serviceProvider)
    {
        Configuration = configuration;

        var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);


        Configuration = builder.Build();

    }

    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<SchoolContext>(option =>
            option.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));


        services.AddScoped<IStudentService, StudentService>();

        services.AddMvc();
    }

    // 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("/Home/Error");
        }

        app.UseStaticFiles();

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

我应该怎么做才能解决这个问题?

What should I do to resolve this problem?

推荐答案

StudentService 期望 DbContext 但容器不知道如何根据您当前的启动来解决它.

StudentService expects DbContext but the container does not know how to resolve it based on your current startup.

您需要将上下文显式添加到服务集合中

You would need to either explicitly add the context to the service collection

启动

services.AddScoped<DbContext, SchoolContext>();
services.AddScoped<IStudentService, StudentService>();

或更新 StudentService 构造函数以明确期望容器知道如何解析的类型.

Or update the StudentService constructor to explicitly expect a type the container knows how to resolve.

学生服务

public StudentService(SchoolContext context)
    : base(context)
{ 
    //...
}

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