Intermittent error with EF Core: The connection does not support MultipleActiveResultSets

问题

I have an ASP.Net Core application that uses EF Core.

I use ASP.Net Identity and share the same DBContext for my app's entities.

I have set my connection string to an Azure SQL database to have MultipleActiveResultSet=True.

It works for a day or two, but eventually it fails with the error:

The connection does not support MultipleActiveResultSets.

I don't think MARS is the real issue since it worked for the first two days it was up.

I am using ASP.Net Core's built-in DI to set my DbContext.

services.AddDbContext<AppDbContext>(options =>
  options.UseSqlServer(appDbContextConnectionString));

My understanding is that the default lifetime for the DbContext above is Transient (per web request).

Is it alright to share the same DBContext with ASP.Net Identity or should I have a separate one for my app's entities, pointed to the same DB?

I don't know if this is an issue with EF Core, ASP.Net Core or with SQL Azure configuration.

回答1:

I had a similar issue and I found that the problem was that I missed an await statement in front of my method.

FetchStuffFromDBAsync();

Became:

await FetchStuffFromDBAsync();

And the problem was gone.

回答2:

MultipleActiveResultSets=True need to add in connection string.

string connectionString = "Data Source=MSSQL1;Initial Catalog=AdventureWorks;Integrated Security=SSPI;MultipleActiveResultSets=True";

回答3:

Multiple Active Result Sets (MARS) is a feature that works with SQL Server to allow the execution of multiple batches on a single connection. When MARS is enabled for use with SQL Server, each command object used adds a session to the connection.

The MARS feature is disabled by default.

You can enable it like below.

string connectionString = "Data Source=MSSQL1;" +   
    "Initial Catalog=AdventureWorks;Integrated Security=SSPI;" +  
    "MultipleActiveResultSets=True";  

Special Considerations When Using MARS

回答4:

I kept running into this issue too, and setting MultipleActiveResultSet=True in the connection string didn't do much.

My db configuration in Startup.cs is very similar to what you have:

 services.AddEntityFrameworkSqlServer()
         .AddDbContext<MyDbContext>(options =>
           options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"),
            builder => builder.MigrationsAssembly("MyProject")),
            ServiceLifetime.Transient
         );

It turned out that I was getting

The connection does not support MultipleActiveResultSets

because I had several async db queries accessing the same entities. So one db query would retrieve an entity, and a second would have included the same entity through EF Core's new Include method. Also see https://stackoverflow.com/a/46164203/4336725

The reason I had several async db queries was because EF Core does not currently support lazy loading (unlike EF 6). https://github.com/aspnet/EntityFrameworkCore/issues/3797

My workaround was to define several IQueryables with different explicit Include() and ThenInclude().

回答5:

Remove "Connection Timeout" setting from your connection string.

来源：https://stackoverflow.com/questions/46033645/intermittent-error-with-ef-core-the-connection-does-not-support-multipleactiver