ef core sqlconnection tryopen nullreferenceexception - connection-string

Question

I am getting a strange error when I used a pre-built (in our custom base) db context I get the following exception
System.NullReferenceException: Object reference not set to an instance of an object.
at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
at System.Data.SqlClient.SqlConnection.Open()
at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.Open(Boolean errorsExpected)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.BufferlessMoveNext(Boolean buffer)
at Microsoft.EntityFrameworkCore.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext()
at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
at lambda_method(Closure , QueryContext )
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass17_1`1.<CompileQueryCore>b__0(QueryContext qc)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source)
...(ommitted on purpose)
The error will go away if I use a new instance of the same db context. I noticed that when we get a DbConnection with the pre-built context the connection has no connection string but with the new instance it is set correctly.
I use the OnConfiguring to configure the provider as follow:
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
if (!optionsBuilder.IsConfigured)
{
if (_provider == Providers.SqlServer)
{
optionsBuilder.UseSqlServer(_connectionString);
}
else
{
throw new NotImplementedException("Provider not supported");
}
}
}
I put a breakpoint here and everytime the connection string is set to the same values. So I do not understand how one instance of the same context has an empty connection string.
Does anyone know the root cause of the issue?
Thank you,

Answer 1

So this happens because I was disposing a connection retrieved from context.Database.GetDbConnection(). I created polyfills for SqlQuery and ExecuteCommand which needed a connection string. So once one of them was called I will lose the current context's connection.