实体框架SaveChanges如何工作？

Question

I try to understand how EF creates DB requests from object manipulations in code. My test scenario is simple:

using(var context = new Context())
{
var entity = context.Entities.First();
entity.A = "TST";
entity.B = "WrongValue";
context.SaveChanges();
}

My idea is to test, how EF deal with transaction. Change A with correct value and change B with wrong value (non existing FK) I track what happening in SQL Server DB. I execute code and nothing change in DB, that was expected. Strange part is that there are two independant SQL request and I don't understand how EF revert first one.

Answer 1

Both Entity Framework and EntityFramework core code are open source. You can check the code at

1. Entity Framework - Link
2. Entity Framework Core - Link

If you see the internal code of Save method (pasted the code snapshot below) then you can validate that it internally it creates a transaction if an external transaction is not provided.

    internal int SaveChangesInternal(SaveOptions options, bool executeInExistingTransaction)
    {
        AsyncMonitor.EnsureNotEntered();

        PrepareToSaveChanges(options);

        var entriesAffected = 0;

        // if there are no changes to save, perform fast exit to avoid interacting with or starting of new transactions
        if (ObjectStateManager.HasChanges())
        {
            if (executeInExistingTransaction)
            {
                entriesAffected = SaveChangesToStore(options, null, startLocalTransaction: false);
            }
            else
            {
                var executionStrategy = DbProviderServices.GetExecutionStrategy(Connection, MetadataWorkspace);
                entriesAffected = executionStrategy.Execute(
                    () => SaveChangesToStore(options, executionStrategy, startLocalTransaction: true));
            }
        }

        ObjectStateManager.AssertAllForeignKeyIndexEntriesAreValid();
        return entriesAffected;
    }

So your below code will internally wrapped inside a transaction which you can validate in SQL Profiler..

using(var context = new Context())
{
var entity = context.Entities.First();
entity.A = "TST";
entity.B = "WrongValue";
context.SaveChanges();
}

However, SQL profiler does not start logging transaction so you need to configure that in trace setting. See the below screenshot of SQL profiler new Trace setting, here, I have checked Show All events . After that Transaction category is being displayed. You can subscribe for Begin Tran , Commit Tran and Rollback Tran events to validate transaction statements. When you will run your scenario, you can see that Begin and Rollback should be logged.