hmrc-mongo

Provides support to use the Official Scala driver for MongoDB

It is designed to make the transition from Simple Reactivemongo as easy as possible.

Main features

It provides a PlayMongoRepository class to help set up a org.mongodb.scala.MongoCollection, registering the domain model codecs, and creating the indices. Then all queries/updates can be carried out on the MongoCollection with the official scala driver directly.

The model objects are mapped to json with Play json. This library will then map the json to mongo BSON.

Other included features are:

• lock
• cache
• transactions
• test support
• metrix
• work-item-repo

Migration

See MIGRATION for migrating from Simple-reactivemongo.

Adding to your build

In your SBT build add:

resolvers += "HMRC-open-artefacts-maven2" at "https://open.artefacts.tax.service.gov.uk/maven2"

libraryDependencies ++= Seq(
  "uk.gov.hmrc.mongo" %% "hmrc-mongo-play-xx" % "[INSERT_VERSION]"
)

Where play-xx is your version of Play (e.g. play-30).

PlayMongoRepository

Create a case class to represent the data model to be serialised/deserialised to MongoDB

Create JSON Format to map the data model to JSON.

Extend PlayMongoRepository, providing the collectionName, the mongoComponent, and domainFormat.

The mongoComponent can be injected if you register the PlayMongoModule with play. In application.conf:

play.modules.enabled += "uk.gov.hmrc.mongo.play.PlayMongoModule"

Ensure the repository is annotated with javax.inject.Singleton so indexes are only initialised on startup.

@Singleton
class UserRepository @Inject()(
  mongoComponent: MongoComponent
)(implicit ec: ExecutionContext
) extends PlayMongoRepository[User](
  collectionName = "user",
  mongoComponent = mongoComponent,
  domainFormat   = User.mongoFormat,
  indexes        = Seq(
                     IndexModel(Indexes.ascending("name"), IndexOptions().name("nameIdx").unique(true))
                   ),
  extraCodecs    = Seq(
                     new UuidCodec(UuidRepresentation.STANDARD),
                     Codecs.playFormatCodec(AdminUser.mongoFormat),
                     Codecs.playFormatCodec(StandardUser.mongoFormat)
                   )
) {
  // queries and updates can now be implemented with the available `collection: org.mongodb.scala.MongoCollection`
  def findAll(): Future[Seq[User]] =
    collection.find().toFuture()
}

Other parameters:

• indexes - in the above example, the indices were also provided to the constructor. They will be ensured to be created before the Repository is available, by blocking. Mark Indices as background as appropriate.
• optSchema - you may provide a BSONDocument to represent the schema. If provided, all inserts will be validated against this. This may be useful when migrating from simple-reactivemongo to ensure the domainFormat has not changed, if relying on library provided formats (e.g. dates).
• replaceIndexes - by default, the indices defined by indexes parameter will be created in addition to any previously defined indices. If an index definition changes, you will get a MongoCommandException for the conflict. If an index definition has been removed, it will still be left in the database. By setting replaceIndexes to true, it will remove any previously but no longer defined indices, and replace any indices with changed definition. Please check how reindexing affects your application before turning on
• extraCodecs - you may provide extra Codecs in order to support the types you wish to use in your repository. Some examples are:
  • you may want to provide a UuidCodec in order to work with UUIDs as binary values - see UUIDs for more information.
  • Since the Mongo driver uses the runtime class of objects to look up the codec, if you are working with a sealed trait you may want to use Codecs.playFormatSumCodecs to create a codec for each subtype detected. See ADTs for more information.

Lock

This is a utility that prevents multiple instances of the same application from performing an operation at the same time. This can be useful for example when a REST api has to be called at a scheduled time. Without this utility every instance of the application would call the REST api.

There are 3 variants that can be used to instigate a lock:

• LockService for locking for a particular task.
• TimePeriodLockService to lock exclusively for a given time period (i.e. stop other instances executing the task until it stops renewing the lock).
• ScheduledLockService for working with scheduled tasks with variable run times, will wait for current task to finish before allowing another to start.

LockService

Inject MongoLockRepository and create an instance of LockService.

The ttl timeout allows other apps to release and get the lock if it was stuck for some reason.

withLock[T](body: => Future[T]): Future[Option[T]] accepts anything that returns a Future[T] and will return the result in an Option. If it was not possible to acquire the lock, None is returned.

It will execute the body only if the lock can be obtained, and the lock is released when the action has finished (both successfully or in failure).

e.g.

@Singleton
class LockClient @Inject()(mongoLockRepository: MongoLockRepository) {
  val lockService = LockService(mongoLockRepository, lockId = "my-lock", ttl = 1.hour)

  // now use the lock
  lockService.withLock {
    Future { /* do something */ }
  }.map {
    case Some(res) => logger.debug(s"Finished with $res. Lock has been released.")
    case None      => logger.debug("Failed to take lock")
  }
}

TimePeriodLockService

The ttl timeout allows other apps to claim the lock if it is not renewed for this period.

withRenewedLock[T](body: => Future[T]): Future[Option[T]] accepts anything that returns a Future[T] and will return the result in an Option. If it was not possible to acquire the lock, None is returned.

It will execute the body only if no lock is already taken, or the lock is already owned by this service instance. It is not released when the action has finished (unless it ends in failure), but is held onto until it expires.

Note: This implementation does not protect against parallel execution of the body. Every time the lock is refreshed the body will be executed again. If this behaviour is undesirable, then ScheduledLockService may be more appropriate.

@Singleton
class LockClient @Inject()(mongoLockRepository: MongoLockRepository) {
  val lockService = TimePeriodLockService(mongoLockRepository, lockId = "my-lock", ttl = 1.hour)

  // now use the lock
  lockService.withRenewedLock {
    Future { /* do something */ }
  }.map {
    case Some(res) => logger.debug(s"Finished with $res. Lock has been renewed.")
    case None      => logger.debug("Failed to take lock")
  }
}

ScheduledLockService

Seeks to alleviate the limitations faced when trying to lock for the execution of scheduled tasks using the other available locking implementations:

• LockService can result in a scheduled task executing more frequently than desired.
• TimePeriodLockService can result in parallel executions of the same task when the ttl lapses before the task is complete.

When using ScheduledLockService the ttl will be extended if the task is still running. Once the task has completed it will either:

1. Release the lock immediately in the event that the task execution has overrun the scheduler interval.
2. Disown the lock and amend the ttl to reflect the cadence of the scheduled task if it completed inside the regular scheduler interval.

withLock[T](body: => Future[T]): Future[Option[T]] accepts anything that returns a Future[T] and will return the result in an Option. If it was not possible to acquire the lock, None is returned.

It will only execute the body upon the acquisition of a fresh lock.

@Singleton
class LockClient @Inject()(
  mongoLockRepository: MongoLockRepository,
  timestampSupport   : TimestampSupport,
  configuration      : Configuration
)(implicit
  actorSystem: ActorSystem
) {

  val initialDelay = configuration.get[Duration]("myScheduler.initialDelay")
  val interval     = configuration.get[Duration]("myScheduler.interval")

  val lockService =
    ScheduledLockService(
      lockRepository    = mongoLockRepository,
      lockId            = "my-lock",
      timestampSupport  = timestampSupport,
      schedulerInterval = interval
    )

  actorSystem.scheduler.scheduleWithFixedDelay(initialDelay, interval) { () =>
    // now use the lock
    lockService.withLock {
      Future { /* do something */ }
    }.map {
      case Some(res) => logger.debug(s"Finished with $res. Lock has been released.")
      case None      => logger.debug("Failed to take lock")
    }
  }
}

Cache

This is a utility to cache generic JSON data in Mongo DB.

The variants are:

• MongoCacheRepository for storing json data into a composite object which expires as a unit.
• SessionCacheRepository ties the composite object to the session.
• EntityCache which makes it easier to work with a single data type.

MongoCacheRepository

e.g.

@Singleton
class MyCacheRepository @Inject()(
  mongoComponent  : MongoComponent,
  configuration   : Configuration,
  timestampSupport: TimestampSupport
)(implicit ec: ExecutionContext
) extends MongoCacheRepository(
  mongoComponent   = mongoComponent,
  collectionName   = "mycache",
  ttl              = configuration.get[FiniteDuration]("cache.expiry")
  timestampSupport = timestampSupport, // Provide a different one for testing
  cacheIdType      = CacheIdType.SimpleCacheId // Here, CacheId to be represented with `String`
)

The functions exposed by this class are:

• put[A: Writes](cacheId: CacheId)(dataKey: DataKey[A], data: A): Future[CacheItem]

  This upserts data into the cache.

  Data inserted using this method has a time-to-live (TTL) that applies per CacheId. The amount of time is configured by the ttl parameter when creating the class. Any modifications of data for an CacheId will reset the TTL.

  Calling put[String](cacheId)(DataKey("key1"), "value1) and put[String](cacheId)(DataKey("key2"), "value2) with the same cacheId will create the following JSON structure in Mongo:

  {
    "_id": "cacheId",
    "data": {
      "key1": "value1",
      "key2": "value2"
    }
  }

  This structure allows caching multiple keys against a CacheId. As cached values expire per CacheId, this provides a way to expire related data at the same time.

  See EntityCache for a simpler use-case, where key is hardcoded to a constant, to provide a cache of CacheId to value.

• get[A: Reads](cacheId: CacheId)(dataKey: DataKey[A]): Future[Option[A]]

  This retrieves the data stored under the dataKey.

  The DataKey has a phantom type to indicate the type of data stored. e.g.

  implicit val stepOneDataFormat: Format[StepOneData] = ...
  val stepOneDataKey = DataKey[StepOneData]("stepOne")
  
  for {
    _       <- cacheRepository.put(cacheId)(stepOneDataKey, StepOneData(..))
    optData <- cacheRepository.get(cacheId)(stepOneDataKey) // inferred as Option[StepOneData]
  } yield println(s"Found $optData")

• delete[A](cacheId: CacheId)(dataKey: DataKey[A]): Future[Unit]

  Deletes the data stored under the dataKey.

• deleteEntity(cacheId: CacheId): Future[Unit]

  Deletes the whole entity (rather than waiting for the ttl).

• findById(cacheId: CacheId): Future[Option[CacheItem]]

  Returns the whole entity.

  The data can be extracted and converted to your model (with an appropriate Reads[A]) with cacheItem.data.as[A].

  Effectively you can store/update the data in steps and extract all the data at the end.

SessionCacheRepository

A variant of MongoCacheRepository which uses the sessionId for cacheId. This helps, for example, store data from different steps of a flow against the same session.

It exposes the functions putSession, getFromSession and deleteFromSession which require the Request rather than a CacheId.

EntityCache

A variant which makes it easier to work with a single data type, which all expire independently.

Transactions

The trait uk.gov.hmrc.mongo.transaction.Transactions fills the gap of providing withTransaction (as available for the java sync driver) for mongo-scala. It may be removed when this is supported by the official driver.

First confirm whether you actually need to use transactions, they will incur a performance cost.

If you don't need to use an existing Session, it is preferrable to use withSessionAndTransaction which will provide you a session to use.

You will need to provide an implicit TransactionConfiguration. We recommend using TransactionConfiguration.strict for causal consistency, but you can provide your own if you do not need such a strict configuration.

It is also recommended to use the Future rather than the Observable abstraction, since we have noticed a few gotchas with the Observable - e.g. some db functions return Publisher[Void] which silently ignore any further monadic steps.

e.g.

@Singleton
class ModelRepository @Inject() (val mongoComponent: MongoComponent)(implicit ec: ExecutionContext)
  extends PlayMongoRepository[Model](...)
     with Transactions {

  private implicit val tc = TransactionConfiguration.strict

  def replaceAll(seq: Seq[Model]): Future[Unit] =
    withSessionAndTransaction(session =>
      for {
        _ <- collection.deleteMany(session, Document()).toFuture()
        _ <- collection.insertMany(session, seq).toFuture()
      } yield ()
    )

You may see com.mongodb.MongoCommandException, with message: Command failed with error 263 (OperationNotSupportedInTransaction): 'Cannot create namespace ... in multi-document transaction.' if collections are created implicitly on insert/upsert from a transaction, which is not supported until Mongo 4.4. You will need to ensure that the collection is created before the transaction runs. This especially applies to tests.

Encryption

hmrc-mongo doesn't itself provide any encryption support. It is recommend to use crypto-json as provided by crypto.

Tests should ensure the data is stored in the expected encrypted format. You may want to refer to these examples

Streaming

hmrc-mongo does not provide any streaming helpers. This can be achieved with Pekko (or Akka similarly).

Instead of using toFuture to convert a reactivestream (cursor of results) into a Future of a strict sequence, you can wrap with Source.fromPublisher to get a Pekko stream. You can then use the Pekko api to process the stream - e.g.

import import pekko.stream.scaladsl.Source
Source.fromPublisher(collection.find())
  .mapAsync(parallelism = 1)(entry => doForEach(entry): Future[Result])
  .runForeach(res => logger.info(s"processed: $res"))

TTL Indexes

TTL Indexes are generally expected. PlayMongoRepository will log warnings on startup if there is no TTL Index. DefaultPlayMongoRepositorySupport will by default fail the test if there isn't a TTL Index or it points to a non-Date field.

In the exceptional case that a TTL Index is not required, this can be indicated by overriding requiresTtlIndex with false in PlayMongoRepository.

Changes

Version 2.1.0

• Fix in playFormatSumCodecs for enum singletons

Version 2.0.0

• Built for Scala 3 as well as Scala 2.13. Scala 2.12 has been dropped.
• legacyNumbers has been dropped - it has proved unnecessary now simple-reactivemongo migrations have taken place.

Version 1.8.0

• Updates mongo-scala-driver to 5.0

Version 1.7.0

• Targets JVM 11.
• MongoCacheRepository and SessionCacheRepository are easier to use since they support extraIndexes and extraCodecs.

Version 1.5.0

• Adds ScheduledLockService - A locking implementation that makes working with scheduled tasks less painful and more predictable.

Version 1.4.0

• Supports Play 3.0 and Play 2.9. Note, joda time is no longer supported with Play 2.9/3.0 build.

Version 1.3.0

• Restore target JVM 8.

Version 1.2.0

• Made awaits on initialisation configurable. Use hmrc.mongo.init.timeout - default is 5 seconds.

Version 1.0.0

• java.time.LocalDateTime support has been removed.

  It is preferrable to use java.time.Instant for storing DateTime in mongo. Use your own formats if LocalDateTime is required.

• Added checks for TTL Indexes.

  See TTL Indexes

• Deployments will no longer fail if adding a new index takes a long time to apply. Failures to create an index (e.g. conflicting index) will still fail a deployment if they occur immediately (which they typically do).

  If you still need to know when ensureIndexes has finished, you can access PlayMongoRepository#initialised

Version 0.72.0

MongoCacheRepository.get previously returned None for both an empty/expired cache as well as if it failed to deserialise the data. Failure to deserialise will now result in a failed Future.

Version 0.60.0

Drops support for Play 2.7. Only Play 2.8 is supported.

License

This code is open source software licensed under the Apache 2.0 License.