290 posts tagged with ".NET"

A savepoint lets part of a transaction fail while the rest carries on. In EF Core, you create one with CreateSavepointAsync, and EF Core also creates its own around each SaveChanges inside a transaction. If you've seen __EFSavePoint in MySQL's log, that's where it comes from.

BeginTransactionAsync takes an isolation level as its first argument, and that's the whole API. The useful part is knowing what gets sent, how to confirm that MySQL really is using it, and which levels the driver refuses.

Sometimes a decision can't fit in one UPDATE: you need to read a row, think about it in C#, and only then change it, with nobody else changing it in the meantime. SELECT ... FOR UPDATE holds the row while you do that. EF Core has no LINQ method for it, so it takes FromSql.

When a connection drops during COMMIT, nobody knows whether it worked. ExecuteInTransactionAsync handles that moment: it begins, commits and retries for you, and when the commit's outcome is unknown, it calls a function you supply to find out. You still have to give that function something to look for.

Changing a stock count with ExecuteUpdateAsync and recording the reason with SaveChangesAsync looks like one job, but those are two separate transactions unless you say otherwise. If the second fails, the count has changed and nothing explains why. Here's that failure, and the fix.

EnableRetryOnFailure takes a list of numbers, and that's all it takes. With MySQL I needed two more things: to tell a dropped connection from a full pool, which share one number, and to close a broken connection before retrying. A class of your own does both, in about 20 lines.

EnableRetryOnFailure looks like a switch, and with Oracle's MySQL provider, it isn't one: until you list error numbers, it retries nothing. Here's the list I use, how to confirm it's working, and how long a request can wait.

As soon as a DbContext has a retrying execution strategy, a plain BeginTransactionAsync stops working. The strategy has to know the whole group of statements, so it can run them all again. It only takes a wrapper, with one detail in the lambda and one at the top of it.

When a transaction doesn't do what you expected, the first question is whether it began and committed at all. EF Core logs both, at Debug level, under a category of their own. One line in your settings shows them, without turning on everything else.

SaveChangesAsync protects one call. When several calls have to succeed or fail together, you need a transaction of your own, and it takes three lines. The last of them decides everything: without it, nothing you did is saved.