I'm Altering multiple sqlite tables with SQL script by calling ExecuteNonQuery. I want to do this operation in transaction and want to roll it back when anything fails.
I looked at BEGIN TRANSACTION and its clear that I have to call ROLLBACK TRANSACTION when anything goes wrong. But I don't know how could TRY...CATCH (Transact-SQL) kind of thing here.
NOTE: Whole of Sql Script file (which contains many other statements apart from these few statements which needs to be fired in one transaction) is read by .ReadToEnd() and then executed in one go as of now. I want to handle this in sql script file itself and don't want to change the code.
Please take a look at SQLite on conflict clause
Start with BEGIN TRANSACTION
You have to add ON CONFLICT ROLLBACK on your actions
And COMMIT TRANSACTION at the end ;-)
Related
I'm using python3.6 and pymysql 0.7.11.
The call to rollback rolls a transaction back, according to the documentation.
A call to commit finalises a transaction.
My question is whether after a call to rollback it is prudent to call commit ... ?
this is not really a python question but about mysql transactions.
you can read about it at http://www.mysqltutorial.org/mysql-transaction.aspx for example.
in short: you need to start a transaction to rollback or commit it.
usually autocommit is enabled if you don't want to use transactions manually .. in that case mysql creates a transaction for every statement.
I am starting to dabble in tSQLt and a few times have accidentally hit F5 and executed my test proc directly instead of through tSQLt.RunAll, which hoses my entire database. Is there any simple way to roll back that accidental execution instead of restoring my entire database from backup?
The full error is [myDClass].[test myTest] failed: (Error) There is already an object named 'pMyProc_SpyProcedureLog' in the database.[16,6]{,1} (There was also a ROLLBACK ERROR --> The current transaction cannot be committed and cannot be rolled back to a savepoint. Roll back the entire transaction.{tSQLt.Private_RunTest,162})
I checked DBCC OPENTRAN but there aren't actually any transactions listed.
I've been reading a lot lately and I am now very confused how transactions and locking are working and how are related to each other.
When working with SQLite, imagine the following flow:
begin SQLite transaction
run a select statement on a SQLite connection to return values
if condition is met on the returned values, go to step #4, otherwise go to step #5
do the update
commit SQLite transaction
If two threads run same code, is there a possibility that in one of the threads could get what is called a "dirty read" meaning, between the step #3 and step #4, the other thread could run the update (step #4)?
Yes, it's called isolation level: https://www.sqlite.org/isolation.html
I probably misundertood something about SAVEPOINTS in SQLite.
I am using C API in an application, where we run a bunch of inserts, and in case something fails, we should give up on all the inserts alltogether.
I am aware I could BEGIN TRANSACTION for such a simple scenario, but I fear that the scenario could get a more complicated, and nesting might become a requirement, that's why I went for SAVEPOINTS.
Anyway, here is an extract of SQL statements I run:
SQL> SAVEPOINT SAVEPOINT_20170524_172706;
SQL> INSERT, SELECT STATEMENT (no COMMIT or END TRANSACTION)
SQL> ROLLBACK TO SAVEPOINT SAVEPOINT_20170524_172706;
SQL> RELEASE SAVEPOINT_20170524_172706;
Basically I create a new savepoint based on the timestamp, before I start inserting and selecting data from the database.
Then one operation fails and I need to bail out, so I rollback to the savepoint I just created.
In the end I want to get rid of the savepoint I wont need anymore, since I dont want to clutter the database with useless savepoints, hence I ran RELEASE . In this case I find myself with the database filled with all the data inserted by statements that were supposed to be rolled back.
If I dont execute the RELEASE statement, then the database looks just fine, but I wonder what happens with the abandoned SAVEPOINT which will never be referenced anymore.
Which wrong assumption am I making? What happens to SAVEPOINTS if I dont release them, are they going to be 'dropped' as I close the 'connection' to the DB file?
I had PRAGMA journal_mode = OFF
I have some piece of code in my Website which adds the details into tables. Now I want that if some error occurs the previously entered data should be removed. How can I implement it with the help of transactions??
We need more details such as what database you are using and so forth. Basically you do this:
Create a transaction
Do some work in the context of that transaction
Do some more work in the context of that transaction
...
If an exception occurred, rollback the transaction, else commit.