# Driver

We have already mention the concept driver in Main concepts. Drivers are the part of Mongock in charge of dealing with MongoDB.

# Motivation

In order to provide support to different MongoDB versions, Java MongoDB drivers and libraries, we need to separate this connector from the rest of Mongock, so the user can choose the right alternative for him(for example, using directly the Java MongoDB driver or Spring Data library)

It's also important when comes to old version. Users may don't want to upgrade to the last version of MongoDB or driver, but they still need Mongock to be supported for their production deployments.

# How it works

Technically drivers are simple implementations of the same interface which provides the contract between the driver itself and the runner.

The idea is to provide a specific driver for every Java MongoDB driver, library or need. Open source users will be able to add drivers, following the driver specification.

Mongock drivers use two MongoDB collections. The changeLogCollection(called mongockChangeLog by default), where the changeLog history will be stored, and the lockCollection(called mongockLock by default), used for pessimistic synchronisation between Mongock executions.

It's important that all the Mongock executions that need to be synchronised(different services or instances using the same MongoDB database) use the same lockCollection. This is the only way they can be synchronised

Also ensure that the right changeLogCollection is used in order to prevent Mongock from re-running migrations undesirably. If you need to migrate from another changeLogCollection or from another legacy migration framework, please refer to [Legacy migration](v4/legacy-migration) for more information.

# Building time: Driver

When use it the annotation approach, you just need to import the required Mongock driver dependency, annotate your SpringBootApplication with @EnableMongock and everything is done for you. All the configuration should be provided via properties file.

However, if you opt for the manual builder approach, you need to create the driver yourself and give it to the Mongock builder.

# Configuration

Driver configuration is very simple, but there are still a couple of properties you can configure related to the collections and lock parameters

Configuration parameter	Default value	Description
changeLogRepositoryName	mongockChangeLock	The name of the repository where the change log history will be stored
lockRepositoryName	mongockLock	The name of the repository where the pessimistic lock will be stored stored
changeLogCollectionName	mongockChangeLock	Deprecated. Use changeLogRepositoryName
lockCollectionName	mongockLock	Deprecated. Use lockRepositoryName
LockAcquiredForMinutes	3	Number of minutes mongock will acquire the lock for. It will refresh the lock when is close to be expired anyway
maxWaitingForLockMinutes	4	Max minutes mongock will wait for the lock in every try. If the time the lock is reserved for is greater than this value, a LockCheckException is thrown.
maxTries	3	Max tries when the lock is held by another mongock instance
indexCreation	true	If false, Mongock won't create the required indexes for LockCollection and ChangeLogCollection.But it will still check they are created, so you must do it manually.
disableTransaction	false	If true, Mongock won't use transactions to perform the migration. Only available for builder approach, no properties.

properties

mongock:
  change-log-repository-name: newChangeLogCollectionName
  lock-repository-name: newLockCollectionName
  lock-acquired-for-minutes: 3
  max-waiting-for-lock-minutes: 4
  max-tries: 3
  index-creation: false

v3-driver

MongoCore3Driver driver = MongoCore3Driver.withDefaultLock(mongoDatabase);
//or .withLockSetting(mongoTemplate, acquiredForMinutes, maxWaitingFor, maxTries);
driver.setChangeLogRepositoryName("newChangeLogCollectionName");
driver.setLockRepositoryName("newLockCollectionName");
driver.setIndexCreation(false);

sync-v4-driver

MongoSync4Driver driver = MongoSync4Driver.withDefaultLock(mongoDatabase);
//or .withLockSetting(mongoTemplate, acquiredForMinutes, maxWaitingFor, maxTries);
driver.setChangeLogRepositoryName("newChangeLogCollectionName");
driver.setLockRepositoryName("newLockCollectionName");
driver.setIndexCreation(false);

springdata-v2-driver

SpringDataMongo2Driver driver = SpringDataMongo2Driver
.withDefaultLock(mongoTemplate);
//or .withLockSetting(mongoTemplate, acquiredForMinutes, maxWaitingFor, maxTries);
driver.setChangeLogRepositoryName("newChangeLogCollectionName");
driver.setLockRepositoryName("newLockCollectionName");
driver.setIndexCreation(false);

springdata-v3-driver

SpringDataMongo3Driver driver = SpringDataMongo3Driver
.withDefaultLock(mongoTemplate);
//or .withLockSetting(mongoTemplate, acquiredForMinutes, maxWaitingFor, maxTries);
driver.setChangeLogRepositoryName("newChangeLogCollectionName");
driver.setLockRepositoryName("newLockCollectionName");
driver.setIndexCreation(false);

# Transactions

For transactions, please go to Transactions section.