I'm using Laravel 5.2.
I would like to know what are the differences between :
DB::beginTransaction() and DB::transaction()
DB::commitTransction() and DB::commit()
DB::rollbackTransction() and DB::rollback()
Any helps would be appreciated.
DB::beginTransaction() will only begin a transaction, while for DB::transaction() you must pass a Closure function that will be executed inside a transaction.
So this:
DB::transaction(function() {
// Do something and save to the db...
});
is the same as this:
// Open a try/catch block
try {
// Begin a transaction
DB::beginTransaction();
// Do something and save to the db...
// Commit the transaction
DB::commit();
} catch (\Exception $e) {
// An error occured; cancel the transaction...
DB::rollback();
// and throw the error again.
throw $e;
}
As you can see, DB::transaction() is a "helper" function to avoid writing code to catch errors, begin a transaction, commit the transaction, and optionally rollback (cancel the transaction) if an error occured.
If you have a more complex logic, or need an specific behaviour, you will manually build your transaction; if your logic is rather simple, DB::transaction() is the way to go.
As for DB::commitTransaction() and DB::rollbackTransaction(), I can't find information.
It's a good practice to check the source code of the things you use, because you will learn how they are written, as well as how to write. Here's the file with the source for these methods.
From Laravel 6 to use Transactions must be use the following helper functions.
use Illuminate\Support\Facades\DB;
try {
// For Begin a transaction
DB::beginTransaction();
// Do something
// Commit the transaction
DB:: commit();
} catch (\Throwable $e) {
// An error occured
DB::rollback();
// and throw the error again.
throw $e;
}
if you use the DB::commitTransaction(); function, get error undefined function.
Related
Let's say I have a function that modifies a database. This could be anywhere from one query to multiple queries in a transaction. In any of these modifications we want to make sure all queries are successful. Thankfully for transactions, if one of these fails I have a way of making sure none of the changes are made permanent.
Now let's say I also have a log that needs to be written to to make note of the change (s). How could I make sure that both the modifications are made and the log written?
I could always do a try/catch on either but say for instance my queries are successful but my log is unsuccessful. How could I then go back and undo all of the modifications to the database?
Would something like this be effective and/or advisable?
try {
$db->connect();
$db->mysqli->begin_transaction();
// series of queries
...
// log to file
$db->mysqli->commit();
} catch (exception $e) {
$db->mysqli->rollback();
$db->mysqli->close();
}
Wanted to make note of some behaviors I observed while testing this. If you place the commit() before the log, the database changes will not roll back even if an exception is caught while logging.
The data will be stored in the database once you call commit() or trigger an implicit commit. For example, this will not make any changes to the database because there is no commit:
$mysqli->begin_transaction();
$mysqli->query('INSERT INTO test1(val) VALUES(2)');
// end of script's execution
In your little example, the transaction will be rolled back as long as your logging functionality stops the execution or throws an exception.
$db->connect();
try {
$db->mysqli->begin_transaction();
// series of queries
...
// log to file
throw new \Exception(); // <-- This will prevent commit from executing.
$db->mysqli->commit();
} catch (\Exception $e) {
// An exception? That's ok, we'll try something different instead.
$db->mysqli->rollback();
}
You need to call rollback only if you want to recover from the exception and clear the unsaved buffer. The only time you should ever catch exceptions is if you want to somehow recover from it and do a different thing. Otherwise, your code could be simplified by removing try-catch and rollback altogether.
However, it is a good idea to catch exceptions in transactions and roll it back explicitly as soon as possible, even when you do not want to recover. It can prevent an issue if you catch the exception somewhere else in your code and you try to execute other DB actions. The unsaved data is still in the buffer until you close the session or roll back! This is why you would often see code like this:
$db->connect();
try {
$db->mysqli->begin_transaction();
throw new \Exception(); // <-- Something throws an exception
$db->mysqli->commit();
} catch (\Exception $e) {
// rollback unsaved data, but rethrow the exception as we do not know how to recover from it here
$db->mysqli->rollback();
throw $e;
}
I am using laravel 4 and trying to use commit and rollback functions. But functions are not working for me.
I am following laravel documentations (https://laravel.com/docs/4.2/database#database-transactions) but still its not working.
Here is my code :
DB::transaction(function() use ($product)
{
DB::table('products')->insert($product);
DB::rollBack();
});
Its creating new entry in products table. which is wrong.
In your example, the transaction will only be rolled back when there is an exception.
Note: Any exception thrown within the transaction closure will cause the transaction to be rolled back automatically.
You have to manually start your transaction with DB::beginTransaction() and end it with DB::rollback() or DB::commit()
It is also possible to do this within a try catch statement.
try {
DB::beginTransaction();
// Do something
DB::commit();
} catch (\Exception $e) {
DB::rollback();
throw $e;
}
I have used DB::transaction function in my controller like this,
public function store(){
$plant = new Plant;
DB::transaction(function()
{
Plant::create(request(['name','plant_code','place']));
});
}
I want to know the way I have used the function is ok and i need to verify is it working correctly?
As the documentation illustrate you have two choices :
Automatic transaction with Closure :
You may use the transaction method on the DB facade to run a set of
operations within a database transaction. If an exception is thrown
within the transaction Closure, the transaction will automatically be
rolled back. If the Closure executes successfully, the transaction
will automatically be committed. You don't need to worry about
manually rolling back or committing while using the transaction
method
DB::transaction(function () {
// Interacting with the database
DB::insert(...);
DB::insert(...);
DB::insert(...);
});
Manually Using Transactions :
If you would like to begin a transaction manually and have complete control over rollbacks and commits, you may use the beginTransaction method on the DB facade:
DB::beginTransaction();
You can rollback the transaction via the rollBack method:
DB::rollBack();
Lastly, you can commit a transaction via the commit method:
DB::commit();
The manually use of the transactions is linked to the try catch block like this :
DB::beginTransaction();
try {
// Interacting with the database
DB::insert(...);
DB::insert(...);
DB::insert(...);
DB::commit(); // Commiting ==> There is no problem whatsoever
} catch (\Exception $e) {
DB::rollback(); // rollbacking ==> Something went wrong
}
For testing the transaction you can run your example without throwing any exception ==> expected result : all fine the Plant will be created.
And if you throw an exception the transaction will be rollbacked and the Plant will not be created in the database :
public function store(){
$plant = new Plant;
DB::transaction(function()
{
Plant::create(request(['name','plant_code','place']));
throw new ModelNotFoundException("Just for testing :)");
});
}
Add use Illuminate\Database\Eloquent\ModelNotFoundException; at the top of the controller ;)
Consider the following scenario:
I open a new connection to MySQL, using mysqli extension
I start a transaction
I do some queries on the MySQL database and to some php computation
Either MySQL or php may throw some exceptions
I commit the transaction
(pseudo) code:
$sql = new mysqli();
...
{ //some scope
$sql->query("START TRANSACTION");
...
if (something)
throw Exception("Something went wrong");
...
$sql->query("COMMIT"); // or $sql->commit()
} //leave scope either normally or through exception
...
$sql->query( ... ); // other stuff not in transaction
If all the above is in some big try catch block (or perhaps even the exception is uncaught) the transaction will remain unfinished. If I then try to do some more work on the database, those actions will belong to the transaction.
My question is: is there some possible mechanism that would permit me to automatically send $sql->rollback() when I leave the transaction-creating scope in an abnormal way?
Some notes:
mysqli::autocommit is not the same as a transaction. It is just a setting for autocommit you turn on or off. Equivalent to MySQL SET autocommit.
mysqli::begin_transaction is not documented and I don't know what is its precise behavior. Will it call rollback when the mysqli object dies for example?
The Command mysqli::begin_transaction is the same (object oriented way) as your $sql->query("START TRANSACTION");;
There is no way, to auto rollback on exception.
You can only comit, if everything has success. Then it will be a "auto rollback" if not. But this way, you will have trouble very soon, if you have more then one commit.
So your current code is allready very good. I would do it the full OOP way:
$sql->begin_transaction();
try {
$sql->query('DO SOMETHING');
if(!true) {
throw new \Exception("Something went wrong");
}
$sql->commit();
}
catch (\Exception exception) {
$sql->rollback();
}
You also can write your own Exception:
class SqlAutoRollbackException extends \Exception {
function __construct($msg, Sql $sql) {
$sql->rollback();
parent::__construct($msg);
}
}
But you still need to catch it.
You cannot automatically rollback on exception, but with a little code you can do what you want. Even if you already are in a try-catch block you can nest them for your transaction section, such as this:
try {
$sql->query("START TRANSACTION");
...
if (something)
throw new PossiblyCustomException("Something went wrong");
...
$sql->query("COMMIT");
} catch (Exception $e) { //catch all exceptions
$sql->query("ROLLBACK");
throw $e; //rethrow the very same exception object
}
Even if you use the most generic catch Exception, the actual type of the exception is known. When you rethrow, it can still be caught by PossiblyCustomException later. Thus, all the handling you already have remains unaffected by this new try-catch block.
So you want to either commit the transaction or rollback the transaction if there was a problem, and there are many ways that a problem could occur - either through a mysql error or php throwing an exception. So why not set up a flag at the start of the transaction, set that flag when the transaction ready to be committed, and check the state of the flag when the process is done to see if a rollback is needed?
If you are afraid of globally scoped variables you could use an overly complicated Singleton class or some kind of static variable for this, but here is the basic idea:
function main() {
global $commit_flag = false;
start_transaction();
doEverything();
if ($commit_flag) {
commit_transaction();
} else {
rollback_transaction();
}
}
function doEverything() {
global $commit_flag;
try {
/* do some stuff that may cause errors */
$commit_flag = true;
} catch { ... }
}
You can handle mysql exceptions using DECLARE ... HANDLER Syntax, but I don't find it proper to try to handle them through PHP !
BEGIN
DECLARE EXIT HANDLER FOR SQLEXCEPTION ROLLBACK;
START TRANSACTION;
INSERT INTO Users ( user_id ) VALUES('1');
INSERT INTO Users ( user_id ) VALUES('2');
COMMIT;
END;
More information can be found here :
http://dev.mysql.com/doc/refman/5.5/en/declare-handler.html
After looking into using try catch blocks for my Pdo statements is it really a benefit? Does this just slow your code down?
I believe that there should be a try catch around the connection command in case the database connection fails. But does there really need to be try catch around each pre prepared statement? These should never change and never really error out.
Any thoughts?
I'm using Php and MySql.
There is no benefit to this:
try {
// exec statement
// exec statement
}
catch (Exception $e) {
// do nothing
}
If you aren't going to do anything with the error and provide a reasonable solution, then you may as well let the exception bubble up to the application's main "something went wrong" error page.
But you may want to do this:
// begin transaction
try {
// exec statement
// exec statement
// commit transaction
}
catch (Exception $e) {
// rollback transaction
// handle error or rethrow $e;
}
And prepared statements can throw exceptions. Perhaps a unique key is violated, or a foreign key constraint is, etc.
But the main point is, you don't use exceptions to hide or silence errors. You use them to catch an error, process it intelligently, and continue on accordingly.