Blazor Server自定义DbContext集成Identity及DbContextFactory报错解决

问题场景 #

需要替换Blazor Server默认的ApplicationDbContext为自定义OpmContext，同时要在Razor页面或自定义服务中注入IDbContextFactory<OpmContext>使用。

默认Program.cs代码：

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));

修改后的代码：

Program.cs #

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");
void BuildOptions(DbContextOptionsBuilder options) => options.UseSqlServer(connectionString).EnableSensitiveDataLogging(); // todo: not for production

builder.Services.AddDbContext<OpmContext>(BuildOptions);
builder.Services.AddDbContextFactory<OpmContext>(BuildOptions);

builder.Services.AddDatabaseDeveloperPageExceptionFilter();
builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
    .AddEntityFrameworkStores<OpmContext>();

自定义DbContext #

public class OpmContext : IdentityDbContext 
{
    public OpmContext(DbContextOptions<OpmContext> options) : base(options)
    {
    }
}

异常信息 #

System.AggregateException: 'Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: Microsoft.EntityFrameworkCore.IDbContextFactory`1[Foo.Bar.Data.OpmContext] Lifetime: Singleton

解决方案 #

问题根源是同时注册AddDbContext和AddDbContextFactory时，DbContext的生命周期与Identity依赖的Scoped实例冲突，且重复配置导致服务注册异常。调整注册逻辑如下：

修改Program.cs代码 #

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");

// 统一配置DbContextOptions
builder.Services.AddDbContextOptions<OpmContext>(options =>
{
    options.UseSqlServer(connectionString)
           .EnableSensitiveDataLogging(); // 生产环境请移除
});

// 注册DbContextFactory（默认生命周期为Singleton，符合要求）
builder.Services.AddDbContextFactory<OpmContext>();

// 注册Scoped生命周期的OpmContext供Identity使用，通过Factory创建实例
builder.Services.AddScoped(sp => 
    sp.GetRequiredService<IDbContextFactory<OpmContext>>().CreateDbContext());

builder.Services.AddDatabaseDeveloperPageExceptionFilter();
builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
    .AddEntityFrameworkStores<OpmContext>();

说明 #

1. 先通过AddDbContextOptions统一配置DbContext的选项，避免重复配置导致的冲突
2. 只注册AddDbContextFactory来提供工厂实例，满足注入IDbContextFactory<OpmContext>的需求
3. 手动注册Scoped生命周期的OpmContext，通过工厂创建实例，确保Identity能获取到符合其生命周期要求的DbContext实例
4. 自定义DbContext继承IdentityDbContext的代码无需修改，已满足Identity的基础要求

内容的提问来源于stack exchange，提问作者juFo