1. The
Even-Darker Art
of
Rails Engines

2. @lazyatom

3. github.com/lazyatom/engines

4. Rails 2.3

5. history

6. November 2005

7. it’s distracting!

8. reuse is overrated!

9. Evil! Evil!
Evil!
Evil!
Evil!
Evil!
Evil!
Evil! Shit!

10. eek!

11. appable_plugins

12. desert

13. merb slices?

15. engines

16. !quot;#$%&!quot;#$'#(%&$#)&!quot;#$%&*$+,#-.!)
!quot;#$%&'()
$$*%&'()$++,$-'%!.%&'()./0#'12%)/'0
quot;0!
3$405/0quot;6$%1quot;$7-(5/06$8/)9$%0$%77:$!/1quot;;)'1<=
!quot;#$quot;05/0quot;>
$$9%6.%77.!/1quot;;)'1<>
quot;0!
3$?quot;)(106$)1(quot;$/#$)9quot;$quot;05/0quot;$69/76$8/)9$%$1'()/05$#/-quot;
!quot;#$1'()quot;!>
$$@/-quot;=quot;A/6)>B1'()/05.#/-quot;C
quot;0!
!quot;#$D/quot;8.7%)9
$$@/-quot;=E'/0B!/1quot;;)'1<F$G%77GF$GD/quot;86GC
quot;0!

17. app/controllers/
models/
helpers/
views/
metal/

18. *$+,#-&quot;**&23-'!3$$(!&*$+,#-523-'!3$$(!.!)
;-%66$H-(5/0I'0)1'--quot;1/0/1**$#2quot;'#3-43-'!3$$(!
$$!quot;#$/0!quot;A
$$$$1quot;0!quot;1$J)quot;A)$,K$LMquot;--'F$H-(5/0NL
$$quot;0!
quot;0!

19. 9quot;-7quot;1$J%--
won’t load from your plugin

20. Ticket #1905

21. config/routes.rb

22. *$+,#-&23-6#,&!3+'(%.!)
O;)/'0I'0)1'--quot;1JJ?'()/05JJ?'()quot;6=!1%8$!'$+2%7+
$$2%7=;'00quot;;)$G:7%)9GF$J;'0)1'--quot;1$,K$L7-(5/0LF$
$$$$$$$$$$$$$$$$$$$$$$$J%;)/'0$,K$L/0!quot;AL
quot;0!

23. top precedence

24. in your plugin:
O;)/'0I'0)1'--quot;1JJ?'()/05JJ?'()quot;6=!1%8$!'$+2%7+
$$2%7=;'00quot;;)$G:7%)9GF$J;'0)1'--quot;1$,K$L7-(5/0LF$
$$$$$$$$$$$$$$$$$$$$$$$J%;)/'0$,K$L/0!quot;AL
quot;0!
in your app:
O;)/'0I'0)1'--quot;1JJ?'()/05JJ?'()quot;6=!1%8$!'$+2%7+
$$3$===$')9quot;1$1'()quot;6$===
$$2%7=;'00quot;;)$G:7%)9GF$J;'0)1'--quot;1$,K$L%77LF$
$$$$$$$$$$$$$$$$$$$$$$$J%;)/'0$,K$L/0!quot;AL
$$3$===$')9quot;1$1'()quot;6$===
quot;0!

25. in your plugin:
O;)/'0I'0)1'--quot;1JJ?'()/05JJ?'()quot;6=!1%8$!'$+2%7+
$$2%7=;'00quot;;)$G:7%)9GF$J;'0)1'--quot;1$,K$L7-(5/0LF$
$$$$$$$$$$$$$$$$$$$$$$$J%;)/'0$,K$L/0!quot;AL
quot;0!
in your app:
O;)/'0I'0)1'--quot;1JJ?'()/05JJ?'()quot;6=!1%8$!'$+2%7+
$$3$===$')9quot;1$1'()quot;6$===
$$2%7=;'00quot;;)$G:7%)9GF$J;'0)1'--quot;1$,K$L%77LF$
$$$$$$$$$$$$$$$$$$$$$$$J%;)/'0$,K$L/0!quot;AL
$$3$===$')9quot;1$1'()quot;6$===
quot;0!

26. Ticket #2592
(also Ticket #329)

27. 785*$+,#-&$#)&785*$+,#-.!)
2'!(-quot;$P<H-(5/0
$$!quot;#$6quot;-#=%!!.1'()quot;6B7quot;*C
$$$$2%7=;'00quot;;)$L:6)(##LF$J;'0)1'--quot;1$,K$L)9/056L
$$quot;0!
quot;0!
O;)/'0I'0)1'--quot;1JJ?'()/05JJ?'()quot;6=!1%8$!'$+2%7+
$$3$<'(1$%77$1'()quot;6===
$$P<H-(5/0=%!!.1'()quot;6B2%7C
$$3$quot;);===
quot;0!

28. what’s missing?

29. public assets

30. copy

31. file clash

32. 83+!5*$+,#-&#-%'quot;$$.!)
2<./2%5quot;6$,$H%)90%2quot;=0quot;8B@/-quot;=!/10%2quot;B..@QR4..CC$S$
$$$$$$$$$$$$$$L%66quot;)6:/2%5quot;6L
)%15quot;)$,$?%/-6=1'')$S$L7(&-/;:/2%5quot;6:2<.7-(5/0L
@/-quot;T)/-6=2U!/1.7B)%15quot;)C
2<./2%5quot;6=;9/-!1quot;0=quot;%;9$!'$+quot;+$
$$$$@/-quot;T)/-6=;7.1Bquot;F$)%15quot;)$S$quot;=&%6quot;0%2quot;C$
quot;0!

33. 83+!5*$+,#-&#-%'quot;$$.!)
2<./2%5quot;6$,$H%)90%2quot;=0quot;8B@/-quot;=!/10%2quot;B..@QR4..CC$S$
$$$$$$$$$$$$$$L%66quot;)6:/2%5quot;6L
)%15quot;)$,$?%/-6=1'')$S$L7(&-/;:/2%5quot;6:2<.7-(5/0L
)%15quot;)=2%Uquot;.6<2-/0UB2<./2%5quot;6C$(0-quot;66$)%15quot;)=quot;A/6)>

34. migrations

35. simple DSL

36. rollback

37. !&:2/51%)quot;:
version
$$VWWXWYWYYVYVZ[.%-79%=1&
VWWXWYWVY[VZ[.&quot;)%=1&
20090101121234
20090102142345
7-(5/0:!&:2/51%)quot;:
2008123123456 $$VWW]YVZYZ[^.5%22%=1&

38. 1%Uquot;$!&J1'--&%;U
version
P/51%)'1=1'--&%;U
20090101121234
P/51%)'13;(11quot;0).Dquot;16/'0
20090102142345
P/51%)'132/51%)quot;!=-%6)
2008123123456 P/51%)'1=5quot;).%--.Dquot;16/'06
BL_4R4I`$Dquot;16/'0$@?aP$$
$$6;9quot;2%.2/51%)/'06LC
=2%7BbJ)'./C=6'1)

39. it gets worse

40. !&:2/51%)quot;:
version
$$WWY.%-79%=1&
WWV.&quot;)%=1&
001
002
7-(5/0:!&:2/51%)quot;:
$$WWY.5%22%=1&

41. http://www.flickr.com/photos/bk2204/475332962/

42. single timeline

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tio
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45. !&:2/51%)quot;:
$$WWY.%-79%=1&
WWV.&quot;)%=1&
WWZ.7-(5/0.)'.WWY=1&
WW[.!quot;-)%=1&
7-(5/0:!&:2/51%)quot;:
$$WWY.5%22%=1&

46. Symlink?
!&:2/51%)quot;:
$$WWY.%-79%=1&
WWV.&quot;)%=1&
Reference?
WWZ.7-(5/0.)'.WWY=1&
WW[.!quot;-)%=1&
Copy &
7-(5/0:!&:2/51%)quot;:
Retimestamp?
$$WWY.5%22%=1&

47. Ticket #2058
interblah.net/plugin-migrations

48. my recommendation?
(for the moment, at least)

49. write a generator
(within your plugin)
c$6;1/7):5quot;0quot;1%)quot;$%;)6.%6.#(.2/51%)/'06
$$$$
$$$quot;A/6)6$$!&:2/51%)quot;
$$$;1quot;%)quot;$$!&:2/51%)quot;:VWWXWWYYYZZd.&-%9=1&
c$===

50. techniques

51. overriding functionality

52. views just work

53. controllers

54. straight override

57. module

61. namespaced

65. playing nice with the
class cache

66. 1/23*8/36/1**$#2quot;'#3-43-'!3$$(!/
!
9quot;%/)((-/!(73:(;/6!37/'9(/73;+$(/
<
<
'!((/)+'/#%/%'#$$/quot;2'#:(<< < <
<<

67. O;)/Dquot;_(77'1)JJequot;7quot;0!quot;0;/quot;6=-'%!.'0;quot;.7%)96

68. ApplicationController
AppController PluginController

69. ApplicationController
PluginController

70. 23-6#,&(-:#!3-7(-'.!)
?%/-6JJQ0/)/%-/fquot;1=1(0$!'$+;'0#/5+
$$3$quot;);===
$$;'0#/5=1quot;-'%!.7-(5/06$,$)1(quot;
$$
quot;0!

71. 83+!5*$+,#-&quot;**&23-'!3$$(!%&,33;523-'!3$$(!.!)
;-%66$g''!I'0)1'--quot;1$h$===
$$(0-'%!%&-quot;
$$
$$3$quot;);$===
quot;0!

72. init.rb woes

73. 785*$+,#-&#-#'.!)
;'0#/5=)'.71quot;7%1quot;$!'
$$_'2quot;O77I-%66=quot;A)quot;0!BP<iquot;9%D/'(1C
$$
quot;0!

74. testing

75. ApplicationController
AppController PluginController

76. ApplicationController
ode
ir C
The
Code
Your
PluginController

78. quot;
$
!
#

80. unit test?

81. test in your own rails
environment?

82. plugin_test_helper

83. I care about testing
my chunk

84. You care about testing
your whole app

85. empower the
developer

86. avoiding fail

87. ;%6quot;$;'!quot;=;'06(2quot;1
$$89quot;0$;'!quot;=%()9'1
$$$$1quot;(6quot;=2'6)-<$,j$:quot;##quot;;)/Dquot;:
$$89quot;0$1%0!B!quot;Dquot;-'7quot;1C
$$$$1quot;(6quot;=)1/;U/quot;1.&().7'66/&-quot;B)1(quot;C
$$quot;-6quot;
$$$$1quot;(6quot;='Dquot;11%)quot;!N
quot;0!

88. consume wisely

89. Nutrition Facts
Serving Size 14 kloc
Amount Per Serving 1 bad engine
Calories 10,666
% Daily Value*
Total Fat 2674g 98%
34%
Long Methods 1578g
7%
God Objects 326g
Stress 320mg 119%
Hairloss 45g 45.8%
Technical Debt 13g 87%
Untested Code 1578mg 34%
7%
Hidden Bugs 326mg
Benefit 1mg 0.1%

90. you will not be able to
write some engines.

91. you will not be able to
use some engines.

92. extract
specific functionality

93. establish some
clear integration points

94. you are customer #1

95. READ the CODE

96. james@lazyatom.com
FIN
lets@gofreerange.com