EFCore无法识别数据库提供者

问题描述

我有一个.Net Core WebApplication项目，其中上下文类位于类库中.如果我在OnConfiguring(DbContextOptionsBuilder optionsBuilder)方法中对连接字符串进行硬编码，则可以生成迁移.因为最好让依赖注入来管理上下文，所以我想将其添加到Startup Class中.但是，当我这样做时，会出现以下错误:

I have a .Net Core WebApplication Project in which the Context Class is in a Class Library. If I hard code the connection string in the OnConfiguring(DbContextOptionsBuilder optionsBuilder) method I can generate migrations. Since it is better to let dependency injection manage the context I would like to add this to the Startup Class. However when I do I get the following error:

DbContext类:

public class CustomerManagerContext : IdentityDbContext<User, Role, long, UserClaim, UserRole, UserLogin, RoleClaim, UserToken>
{
    public CustomerManagerContext() { }
    public CustomerManagerContext(DbContextOptions<CustomerManagerContext> options) : base(options)
    {
    }

    //protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    //{
    //    base.OnConfiguring(optionsBuilder);
    //    optionsBuilder.UseSqlServer("SecretConnectionString");
    //}


    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.Entity<User>().ToTable("Users");
        builder.Entity<Role>().ToTable("Roles");
        builder.Entity<UserClaim>().ToTable("UserClaims");
        builder.Entity<UserRole>().ToTable("UserRoles");
        builder.Entity<UserLogin>().ToTable("UserLogins");
        builder.Entity<RoleClaim>().ToTable("RoleClaims");
        builder.Entity<UserToken>().ToTable("UserTokens");

    }
}

启动类-ConfigureServices方法

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<CustomerManagerContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))
    );

    services.AddEntityFrameworkSqlServer()
        .AddDbContext<CustomerManagerContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddIdentity<User, Role>()
        .AddEntityFrameworkStores<CustomerManagerContext>()
        .AddDefaultTokenProviders();
}

推荐答案

这让我很难受，得到了如下错误:

This bit me hard, getting errors like:

• No database provider has been configured for this DbContext.
• No design-time services were found.
• The server was not found or was not accessible.

• No database provider has been configured for this DbContext.
• No design-time services were found.
• The server was not found or was not accessible.

但是我最终得到了一个相当简单的解决方案/解决方法:

But I ended up with a fairly simple solution/work-around:

• 在解决方案(或命令行)中设置默认的启动项目
您的Startup.cs中的

• 添加迁移项目 :

• Set the default startup-project in your solution (or in your command line)

• in your Startup.cs add the migration-project:

public void ConfigureServices(IServiceCollection services)
{
    var myDbContextAssemblyName = typeof(MyDbContext).Assembly.GetName().Name;
    var connectionString = Configuration.GetConnectionString(MyDbContext.ConnectionStringName);
    services.AddDbContext<MyDbContext>(options => options.UseSqlServer(
        connectionString,
        x => x.MigrationsAssembly(myDbContextAssemblyName)));
        // do more ...
    }

在您的连接字符串中使用 IP地址和端口号(受此corefx问题)，而不是服务器名称/dns(FWIW:).所以现在我的appsettings.Development.json中有此内容:

in your connection-string use the IP-address and port-number (inspired by this corefx issue), instead of the server-name/dns (FWIW: query to get IP).So now I have this in my appsettings.Development.json:

"ConnectionStrings":{ "MyConnectionStringName":数据源= 10.1.2.3,1433；初始目录= MyCatalog；集成安全性= SSPI" }

"ConnectionStrings": { "MyConnectionStringName": "Data Source=10.1.2.3,1433; Initial Catalog=MyCatalog; Integrated Security=SSPI" }

我发现了很多其他建议，并且我还会提到一些看起来很有趣的建议.也许会帮助其他人:

I found a lot of other suggestions, and I will mention a few that seemed interesting. Maybe it will help someone else:

在命令行中提及启动项目和迁移项目

Mention startup-project and migration-project in command-line:

Update-Database -Verbose -Project x.Data -StartupProject x.Web

从代码迁移

也可以在启动，"用于具有本地数据库的应用程序". (我想否则会在多个节点上运行，是否可能同时出现并发问题而启动多个运行时迁移?)

Migrate from code

One can also call migrations at StartUp, "for apps with a local database". (I guess otherwise running on multiple nodes, may start multiple runtime migrations at the same time with concurrency issues?)

myDbContext.Database.Migrate();

在Main.cs中设置DbContext

此EntityFrameworkCore问题指出:

这对我来说不是必需的，因为.Net Core 2 在后台加载配置.

This is not necessary for me, I guess because .Net Core 2 loads the configuration behind the scenes.

此EntityFrameworkCore问题指出:

对我来说这似乎太过分了.

This seems too much a hack to me.

Microsoft文档提到:

他们提到了提供这种设计时DbContext的这些方法:

They mention these ways to provide this design time DbContext:

• 来自应用程序服务:对于作为启动项目的ASP.NET Core应用程序:

• from application services: for an ASP.NET Core app as startup project:

使用没有参数的构造函数

Using a constructor with no parameters

在设计时工厂

From a design-time factory

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