Skip to Content

Wiki source code of WebObjects and Squeryl

Last modified by Ravi Mendis on 2011/04/01 11:14
Show last authors
1 = Squeryl ~= //SQL-like// DSL in Scala =
2
3 Advantages of [[Squeryl>>url:http://squeryl.org/||shape="rect"]] over EOF:
4
5 * Concurrent
6 ** Spawns multiple database connections
7 ** Issues database transactions concurrently
8 * Scala Actor compatible
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
15
16 = Migrating EOF -> Squeryl =
17
18 In contrast to EOF Squeryl maintains its ORM information programmatically - in the classes itself and collectively in a [[schema>>url:http://squeryl.org/schema-definition.html||shape="rect"]]. In keeping with the strongly-typed philosophy of Scala, Squeryl has no dynamic component like EOF (i.e an EO model file).
19
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.
21
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 {{code language="none"}}EOGenericRecord{{/code}}.
25 * Mark the abstract many-To-Many join entities as {{code language="none"}}Abstract{{/code}}.
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 {{code language="none"}}File Names{{/code}} extension to "scala".
31 1. Use the Squeryl EO Templates:
32 1*. _Entity.eotemplate [[template>>doc:WOL.Home.EOGenerator.EOGenerator Templates and Additions.Squeryl _Entity\.eotemplate.WebHome]]
33 1*. Entity.eotemplate [[template>>doc:WOL.Home.EOGenerator.EOGenerator Templates and Additions.Squeryl Entity\.eotemplate.WebHome]]
34
35 {{note title="Note"}}
36 Any custom business "logic" will have to be manually re-written in Scala
37 {{/note}}
38
39 == Differences Between a Squeryl Schema and EO Model/Classes ==
40
41 * Optional attributes (i.e those that {{code language="none"}}allowsNull{{/code}}) are typed as {{code language="none"}}Option[WO:T]{{/code}}
42 * To one relationships that are not mandatory (i.e optional relationships) are also typed as {{code language="none"}}Option[WO:T]{{/code}}
43 * To many relationships are represented as a Squeryl iterable (collection class) as opposed to a {{code language="none"}}NSArray{{/code}}.
44
45 === Use of Scala Collections ===
46
47 ===== 1. Filtering =====
48
49 Instead of using EOQualifiers to filter EOs dynamically, you can apply the type safe filter in Scala:
50
51 {{code}}
52
53 def activeFiles = files.filter(_.active == true)
54
55 {{/code}}
56
57 ===== 2. Iteration =====
58
59 Functional language iteration that's become increasingly popular can be used:
60
61 {{code}}
62
63 activeFiles.foreach(f => {
64 ...
65 })
66
67 {{/code}}
68
69 ===== 3. For-Comprehensions =====
70
71 Here's just an example use of sequence comprehension:
72
73 {{code}}
74
75 def activeFiles = for (file <- files if file.active == true) yield file
76
77 {{/code}}