Coercing and validating user input can lead to painful code. Casting language primitives is done by Ecto, and storage problems that once required thought are solved by convention—time is stored in UTC, money without floating points. Managing our own types often gets ugly, though: standard vs metric; currency conversion; jsonb. Extending Ecto is simple. With custom types, we can separate casting from formatting and dramatically improve the readability and maintainability of applications.

1. Casting against type(s)
…an Ecto story…
by Eric Saxby

2. Prologue

3. Once upon a time…
I used to program in my spare time.
Now I avoid computers whenever
possible.

4. Value vs time…
How we spend our time matters.
Value is created through the quality of
time, not (just) the quantity of time
invested in a pursuit.

8. @jonny_lew

10. Act I

11. @nate_dumlao

13. Elixir Database

14. Elixir Database

16. Form Data Elixir

17. Act II

18. @byrawpixel

19. bit.do/graphicriver

20. Schema

22. Template

23. Controller
controller lets
the schema do
the work

26. Ecto.Type

27. Ecto.Type

29. Controller
controller turns
binary into a
NaiveDateTime

30. Schema
…or maybe the
schema should
do the work?

31. tylernixcreative.com

33. Schema

34. ????? units ?????
Schema

35. metric
Schema

36. Template

37. Schema

38. we can convert metric
to imperial, and vice
versa
decimal in, decimal out

39. Template

40. Controller
more controller
logic?

41. Schema
more schema
logic?

43. Migration

44. Schema
nothing changes
I hope we remember to do this everywhere

45. Intermission

46. @matt_henry_photo

47. Act III

48. unsplash.com/@awmleer

54. Elixir Database

55. Elixir Database

56. Form Data Elixir

57. Form Data Elixir
what does the user see?
Note:
String.to_existing_atom()

58. Schema

60. Template

65. @souvenirpixels

67. yaaaaay structs!

68. no more Decimal;
receive/return %Mass{}
only convert when
necessary

69. is a :decimal in the database
now Mass is a Type

70. comes out of the database in
metric
now Mass is a Type

71. converted to metric when
going into the database
now Mass is a Type

72. how do we handle user input?
…weʼll come back to this
now Mass is a Type

73. Schema
mass as :decimal

74. mass as Mass

75. Template
instead of text_input/4…

76. Template
…we have mass_input/4

77. View
two fields, [value] and [units]
Form implements text_input/4
most of this comes from
generic_input/4

80. ?????

81. turn into a Mass,
convert to :metric

82. convert in both cast/1
and dump/1…
%Mass{} may be made
without a cast

83. unsplash.com/@abhithelucifer

84. Type
https://www.amberbit.com/blog/2017/8/3/time-zones-in-postgresql-elixir-and-phoenix/
UTCDatetime wraps
:utc_datetime
cast receives zone
from the form,
shifts value to UTC

85. View
two fields,
[timestamp]
and [zone]
convert to user's
time zone

87. unsplash.com/@octoberroses

88. jsonb column
may be 2D or 3D
height x width
optional depth

91. unsplash.com/@thoughtcatalog

92. PostgreSQL has monetary types!

93. that uses the current locale…

94. Ecto only sees individual fields,
not relationships between
multiple fields

100. It's complicated!
I can't give you one recommendation.

101. • Currencies have different scales and precisions
• Not all currencies are base 10
• You may not want to automatically convert between currencies,
depending on your business, your payment gateway(s),
your bank(s), etc
• When you convert currencies, you may want to store the
exchange rate at the time of the transfer

103. Credits
Sparta Science
Aaron Graham
Abraham Choe
Andrew Aunelle
Diana Chou
Erik Hanson
Greg Woodward
Harold Tafur
Kelly Felkins
Jeff Rosen
Mark Sherwood
Nick Chaffee
https://www.amberbit.com/blog/2017/8/3/time-zones-
in-postgresql-elixir-and-phoenix/
https://unsplash.com
https://www.pexels.com
unattributed photos are attributable to me

104. Questions?