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WebObjects and Squeryl

Last modified by Ravi Mendis on 2011/04/01 11:14

Squeryl = SQL-like DSL in Scala

Advantages of Squeryl over EOF:

  • Concurrent
    • Spawns multiple database connections
    • Issues database transactions concurrently
  • Scala Actor compatible
    • Immutable object model/graph
    • Explicit transaction control
  • Type Safety
    • Better suited for database/business "logic".
       E.g: Exploits the compiler and IDE to catch exceptions at compile time rather than at run-time.
  • Uses Scala Collections

Migrating EOF -> Squeryl

In contrast to EOF Squeryl maintains its ORM information programmatically - in the classes itself and collectively in a schema. In keeping with the strongly-typed philosophy of Scala, Squeryl has no dynamic component like EOF (i.e an EO model file).

EOF has the ability to generate classes in Java (and in Objective-C prior to WebObjects 4.5) because enforcing type has become customary in enterprise environments. We may exploit this feature of EOF to generate a Squeryl schema from an EO model.

Preparing your EO model

  • Make sure all EO entities have a class name (including abstract many-To-many "join" tables). FYI: There can be no support for entities classified as EOGenericRecord.
  • Mark the abstract many-To-Many join entities as Abstract.
  • (Temporary) Ensure all the model entities are in the same package. i.e the package is exclusive to the model.

Generating the Squeryl Schema

  1. Create a .eogen file for your EO model as normal. Only set the File Names extension to "scala".
  2. Use the Squeryl EO Templates:
Warning

Note

Any custom business "logic" will have to be manually re-written in Scala

Differences Between a Squeryl Schema and EO Model/Classes

  • Optional attributes (i.e those that allowsNull) are typed as Option[WO:T]
  • To one relationships that are not mandatory (i.e optional relationships) are also typed as Option[WO:T]
  • To many relationships are represented as a Squeryl iterable (collection class) as opposed to a NSArray.

Use of Scala Collections

1. Filtering

Instead of using EOQualifiers to filter EOs dynamically, you can apply the type safe filter in Scala:


def activeFiles = files.filter(_.active == true)
2. Iteration

Functional language iteration that's become increasingly popular can be used:


activeFiles.foreach(f => {
   ...
})
3. For-Comprehensions

Here's just an example use of sequence comprehension:


def activeFiles = for (file <- files if file.active == true) yield file