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Wiki source code of WebObjects and Squeryl

Version 69.1 by Ravi Mendis on 2011/03/31 23:35
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Ravi Mendis 66.1 1 = Squeryl ~= //SQL-like// DSL in Scala =
Ravi Mendis 54.1 2
3 Advantages of [[Squeryl>>http://squeryl.org/]] over EOF:
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5 * Concurrent
6 ** Spawns multiple database connections
7 ** Issues database transactions concurrently
8 * Scala Actor compatible
9 ** Immutable object model/graph
Ravi Mendis 60.1 10 ** Explicit transaction control
Ravi Mendis 62.1 11 * Type Safety
Ravi Mendis 54.1 12 ** Better suited for database/business "logic".
13 E.g: Exploits the compiler and IDE to catch exceptions at compile time rather than at run-time.
Ravi Mendis 68.1 14 * Uses Scala Collections
Ravi Mendis 54.1 15
16 = Migrating EOF -> Squeryl =
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18 In contrast to EOF Squeryl maintains its ORM information programmatically - in the classes itself and collectively in a [[schema>>http://squeryl.org/schema-definition.html]]. In keeping with the strongly-typed philosophy of Scala, Squeryl has no dynamic component like EOF (i.e an EO model file).
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20 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.
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22 === Preparing your EO model ===
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24 * 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##.
25 * Mark the abstract many-To-Many join entities as ##Abstract##.
26 * (Temporary) Ensure all the model entities are in the same package. i.e the package is exclusive to the model.
27
28 === Generating the Squeryl Schema ===
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30 1. Create a .eogen file for your EO model as normal. Only set the ##File Names## extension to "scala".
31 1. Use the Squeryl EO Templates:
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33 *
34 ** Entity.eotemplate [[template>>WOL:Squeryl _Entity.eotemplate]]
35 ** Entity.eotemplate [[template>>WOL:Squeryl Entity.eotemplate]]
36
37 {{note title="Note"}}
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39 Any custom business "logic" will have to be manually re-written in Scala
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41 {{/note}}
42
43 == Differences Between a Squeryl Schema and EO Model/Classes ==
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45 * Optional attributes (i.e those that ##allowsNull##) are typed as ##OptionT##
46 * To one relationships that are not mandatory (i.e optional relationships) are also typed as ##OptionT##
47 * To many relationships are represented as a Squeryl iterable (collection class) as opposed to a ##NSArray##.
Ravi Mendis 64.1 48
49 === Use of Scala Collections ===
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51 ===== 1. Filtering =====
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53 Instead of using EOQualifiers to filter EOs dynamically, you can apply the type safe filter in Scala:
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55 {{code}}
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Ravi Mendis 68.1 57 def activeFiles = files.filter(_.active == true)
Ravi Mendis 64.1 58
59 {{/code}}
Ravi Mendis 68.1 60
61 ===== 2. Iteration =====
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63 Functional language iteration that's become increasingly popular can be used:
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65 {{code}}
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67 activeFiles.foreach(f => {
68 ...
69 })
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71 {{/code}}
72
73 ===== 3. For-Comprehensions =====
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75 {{code}}
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77 def activeFiles = for (file <- files if file.active == true) yield f
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79 {{/code}}