Reuse Spray JSON formatters as serialisers for MongoDB persistence in Scala, and get access to a useful CRUD for performing simple searches.

ScalaD is an implicit heavy API: users are advised to re-read the Implicits chapter from Odersky's Book if feeling overwhelmed.

When all relevant marshallers and mongo settings are implicitly in scope, using ScalaD is as simple as:

val entity = ...

val crud = new SprayMongo

crud.create(entity)

val update = entity.copy(name = "Bar")
crud.findAndReplace("id":>entity.id, update)

val morePopular = crud.searchAll("count":> {"$gte":> update.count})  // awesome DSL for JSON

However, anybody using this library is strongly encouraged to read the MongoDB Documentation as it is often necessary to get close to the raw queries to understand what is happening.

In particular, anybody wishing to use the Aggregation Framework, or perform partial updates ($set), will have to revert to the Java API to a large extent (ScalaD provides some nice convenience conversions for doing this).

We are aware that there is a lot of boilerplate involved in setting up Spray JSON implicits – we are hoping to automatically generate this code in a future release.

The best place to find more examples are the specs and the akka-patterns project:

• PersistenceSpec.scala
• Akka Patterns

Because we're using Spray JSON to do the marshalling, it means that only JSON compatible objects are naturally supported by ScalaD.

However, JSON is missing a few keys object types, such as: Date, UUID and any distinction between number types.

MongoDB BSON is also missing a few key object types, such as: UUID, BigInt and BigDecimal. Indeed, MongoDB treats numbers as primitive types and has no support for arbitrary precision numbers.

We provide JSON marshallers for UuidMarshalling and DateMarshalling which creates JSON marshalled forms of UUID and Date objects to look like this (so they can still be understood by endpoint clients)

{"$uuid": "550e8400-e29b-41d4-a716-446655440000"}
{"$date": "2013-02-04T17:51:35.479+0000"} // "yyyy-MM-dd'T'HH:mm:ss.SSSZ"

the serialisation layer will ensure that these are saved as BinData and DateFormat accordingly.

If you want to use arbitrary precision numbers, we provide case classes (and Spray JSON marshallers) called StringBigInt and StringBigDecimal which marshall to String.

Be warned that although Spray JSON will correctly marshall raw BigInts and BigDecimals, MongoDB will silently drop the precision (ScalaD will detect this and create a log for every object that loses precision, so hopefully this is caught at development time).