Does DbTransactionInterceptor always run, when using EF Core 6.0?

Question

I am looking into building an interceptor for my application. One of the interceptors I need is for when I use transactions. While playing around with one, I noticed that it is always triggered - even when I have not started a transaction. Is this expected behaviour?

The following code gives me this output:

transaction triggered
transaction triggered

using System;
using System.Data.Common;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;

var context = new TestContext();

context.Database.EnsureDeleted();
// this triggers the transaction interceptor. I assume a transaction is started when creating a db.
context.Database.EnsureCreated();
var test = new TestClass()
{
    Name = "Morten",
};
context.TestClasses.Add(test);
context.SaveChanges(); // this triggers the transaction interceptor - which I didn't expect

class TestContext : DbContext
{
    public DbSet<TestClass> TestClasses { get; private set; } = null!;

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.AddInterceptors(new TestTransactionInterceptor());
        optionsBuilder.UseSqlServer("Data Source=localhost;Initial Catalog=Test;User ID=myuser;Password=mypassword;Multiple Active Result Sets=True");
    }
}

class TestTransactionInterceptor : DbTransactionInterceptor
{
    public override void TransactionCommitted(DbTransaction transaction, TransactionEndEventData eventData)
    {
        Console.WriteLine("transaction triggered");
        return;
    }
}

class TestClass
{
    public int Id { get; set; }
    public string Name { get; set; } = string.Empty;
}

Answer 1

The cause is an implicit transaction.

By default, if the database provider supports transactions, all changes in a single call to SaveChanges are applied in a transaction.

So this means that despite no explicit transaction being created, ef core will do it implicitly - which is what causes the interceptor to be triggered.

https://learn.microsoft.com/en-us/ef/core/saving/transactions#default-transaction-behavior

Thanks to: https://twitter.com/josvandertil/status/1534871408517558274?t=Dl4YZKsTFbWBwgCsttaVlg&s=19