c# - 使用依赖注入(inject)时如何修复 'A second operation started on this context before a previous operation completed...'？

Question

从数据库中读取数据时出现此错误:

A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.

我有以下 ApplicationContext.cs:

public class ApplicationContext : Microsoft.EntityFrameworkCore.DbContext
{
    public ApplicationContext(DbContextOptions<ApplicationContext> options)
        : base(options)
    { }

    public DbSet<MyClass> MyClasses{ get; set; }
}   

下面的ApplicationContextFactory.cs

public class ApplicationContextFactory : IDesignTimeDbContextFactory<ApplicationContext>
{
    public ApplicationContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<ApplicationContext>();
        var connection = "myConnectionString";

        builder.UseSqlServer(connection);

        return new ApplicationContext(builder.Options);
    }
}   

以下 ServiceLoader.cs(我在其中声明 DI):

public static class ServiceLoader
{
    public static void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<IRepository, Repository>();

        var connection = "myConnectionString";
        services.AddDbContext<ApplicationContext>(options => options.UseSqlServer(connection));
    }
}

最后是抛出异常的以下存储库:

public class Repository : IRepository
{
    private ApplicationContext _db;

    public Repository (ApplicationContext db)
    {
        _db = db;
    }

    public List<MyClass> Get()
    {
        _db.MyClasses.ToList();
    }
}

我也曾尝试将 Repository 声明为 Transient 而不是 Singleton，但抛出了类似的错误

'An attempt was made to use the context while it is being configured. A DbContext instance cannot be used inside OnConfiguring since it is still being configured at this point. This can happen if a second operation is started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.'

知道如何解决这个问题吗？谢谢!

Answer 1

就我而言，我发现以下信息很有用:

https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

并在启动时使用重载的 AddDbContext 方法将我的 Db 上下文的生命周期范围更改为 transient :

services.AddDbContext<MyAppDbContext>(options => {
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection"));
        }, ServiceLifetime.Transient);