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Wiki source code of WebObjects and Squeryl

Version 163.1 by Ravi Mendis on 2011/04/01 11:14
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Ravi Mendis 163.1 1 = Squeryl ~= //SQL-like// DSL in Scala =
Ravi Mendis 54.1 2
Ravi Mendis 163.1 3 Advantages of [[Squeryl>>http://squeryl.org/]] over EOF:
Ravi Mendis 54.1 4
5 * Concurrent
Ravi Mendis 155.1 6 ** Spawns multiple database connections
7 ** Issues database transactions concurrently
Ravi Mendis 54.1 8 * Scala Actor compatible
Ravi Mendis 163.1 9 ** Immutable object model/graph
10 ** Explicit transaction control
11 * Type Safety
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.
14 * Uses Scala Collections
Ravi Mendis 159.1 15
16 = Migrating EOF -> Squeryl =
17
Ravi Mendis 163.1 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).
Ravi Mendis 159.1 19
Ravi Mendis 163.1 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.
Ravi Mendis 159.1 21
Ravi Mendis 163.1 22 === Preparing your EO model ===
23
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 ===
29
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:
32
33 *
Ravi Mendis 159.1 34 ** Entity.eotemplate [[template>>WOL:Squeryl _Entity.eotemplate]]
35 ** Entity.eotemplate [[template>>WOL:Squeryl Entity.eotemplate]]
Ravi Mendis 163.1 36
37 {{note title="Note"}}
38
39 Any custom business "logic" will have to be manually re-written in Scala
40
41 {{/note}}
42
43 == Differences Between a Squeryl Schema and EO Model/Classes ==
44
45 * Optional attributes (i.e those that ##allowsNull##) are typed as ##OptionWO:T##
46 * To one relationships that are not mandatory (i.e optional relationships) are also typed as ##OptionWO:T##
47 * To many relationships are represented as a Squeryl iterable (collection class) as opposed to a ##NSArray##.
48
49 === Use of Scala Collections ===
50
51 ===== 1. Filtering =====
52
53 Instead of using EOQualifiers to filter EOs dynamically, you can apply the type safe filter in Scala:
54
55 {{code}}
56
57 def activeFiles = files.filter(_.active == true)
58
59 {{/code}}
60
61 ===== 2. Iteration =====
62
63 Functional language iteration that's become increasingly popular can be used:
64
65 {{code}}
66
67 activeFiles.foreach(f => {
68 ...
69 })
70
71 {{/code}}
72
73 ===== 3. For-Comprehensions =====
74
75 Here's just an example use of sequence comprehension:
76
77 {{code}}
78
79 def activeFiles = for (file <- files if file.active == true) yield file
80
81 {{/code}}