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Whenever insert transactions have AFTER triggers closely connected to the transaction A transaction is a group of SQL statements whose effects are logically connected. Anything from simple queries to inserting, and deleting operations can be considered a transaction, as well as more complex groups of several statements which accomplish a specific task. fields (e.g. a trigger A trigger is a SQL procedure that performs an action when a transaction (INSERT, UPDATE, DELETE) occurs. You can use triggers to perform validation of input data, to automatically generate a value for a newly inserted row, to read from other tables for cross-referencing purposes, or to support alerts through e-mail messages. that performs the file upload), the form data is first inserted into the table, and only then is the trigger executed. If the trigger fails for any reason, the data has already been inserted into the database A database refers to data organized and stored on a computer that can be searched and retrieved by a computer program. Most industrial-strength and many smaller database applications can be addressed using SQL (Structured Query A query is a SQL command that will extract information from the tables of a database. Essentially, a query is a request for information from your database. Language)., which may lead to corrupt or fake entries in your database.
For instance, an image file can get recorded in the database, but the actual file is not uploaded to the server, because the upload trigger failed. Consequently, the image will not be available in your application. A way to avoid this problem is implemented in MX Kollection 3, and is called a roll-back A roll-back is a SQL command which cancels the proposed changes in a pending database transaction and marks the end of the transaction. operation.
More exactly, a roll-back is an ERROR trigger that is executed when the AFTER trigger of an insert transaction has failed to execute correctly. The trigger receives the unique ID of the last inserted record. Its only function is to delete it from the database, thus providing a fail-safe mechanism against corrupted data.
As you can see in the next example, when the file upload trigger fails because of some wrong values, the next thing to be executed is the roll-back trigger:
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