The document discusses using Arel to construct ActiveRecord queries in a more object-oriented way compared to using literal SQL strings. It provides examples of using Arel to select columns, join tables, and add where conditions in a chained method syntax. Some benefits highlighted are that Arel avoids needing to know SQL syntax, provides Ruby syntax checking, and results in more readable queries.

1. ADVANCED AREL
WHEN ACTIVERECORD JUST ISN’T ENOUGH
Author.where(
name: "Cameron Dutro",
username: "@camertron"
)

2. `WHOAMI`
CAMERON DUTRO
INTERNATIONAL MAN OF MYSTERY
US GOVERNMENT
@CAMERTRON
GITHUB.COM/CAMERTRON

3. `WHOAMI`
CAMERON DUTRO
INTERNATIONAL MAN OF MYSTERY
US GOVERNMENT
@CAMERTRON
GITHUB.COM/CAMERTRON

4. `WHOAMI`
CAMERON DUTRO
INTERNATIONAL ENGINEERING
TWITTER, INC
@CAMERTRON
GITHUB.COM/CAMERTRON

6. RAISE YOUR HAND IF...
Posts.find(:all,
joins: [
"JOIN comments ON comments.post_id = posts.id",
"JOIN authors ON authors.id = comments.author_id"
],
conditions: [
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
]
)
2

7. RAISE YOUR HAND IF...
Posts
.joins(
"JOIN comments ON comments.post_id = posts.id",
"JOIN authors ON authors.id = comments.author_id")
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
3/4

9. RAISE YOUR HAND IF...
Posts
.joins(
"JOIN comments ON comments.post_id = posts.id",
"JOIN authors ON authors.id = comments.author_id")
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
3/4

10. HMM, LET’S SIMPLIFY?
Posts
.joins(:comments)
.joins(
"JOIN authors ON authors.id = comments.author_id"
)
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
3/4

11. HMM, LET’S SIMPLIFY?
Posts
.joins(:comments)
.joins(:comments => :author)
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
3/4

13. PROBLEMS
3/4
Posts
.joins(:comments)
.joins(
"JOIN authors ON authors.id = comments.author_id"
)
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)

14. PROBLEMS
.joins(
"JOIN authors ON authors.id = comments.author_id"
)

15. PROBLEMS
.joins(
"JOIN authors ON authors.id = comments.author_id"
)
HAVE TO WRITE “JOIN” AND “ON”

16. PROBLEMS
.joins(
"JOIN authors ON authors.id = comments.author_id"
)
HAVE TO WRITE “JOIN” AND “ON”
HAVE TO KNOW MYSQL SYNTAX

17. PROBLEMS
.joins(
"JOIN authors ON authors.id = comments.author_id"
)
HAVE TO WRITE “JOIN” AND “ON”
HAVE TO KNOW MYSQL SYNTAX
NO SYNTAX CHECKING

18. PROBLEMS
3/4
Posts
.joins(:comments)
.joins(
"JOIN authors ON authors.id = comments.author_id"
)
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)

19. PROBLEMS
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)

20. PROBLEMS
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
HAVE TO KNOW MYSQL SYNTAX

21. PROBLEMS
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
HAVE TO KNOW MYSQL SYNTAX
CONFUSING TO MATCH ARGUMENTS WITH
QUESTION MARKS

22. PROBLEMS
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
HAVE TO KNOW MYSQL SYNTAX
CONFUSING TO MATCH ARGUMENTS WITH
QUESTION MARKS
NOT OBJECT-ORIENTED

23. PROBLEMS
.where(
"authors.name = ? AND posts.active = ?",
"Barack Obama", true
)
HAVE TO KNOW MYSQL SYNTAX
CONFUSING TO MATCH ARGUMENTS WITH
QUESTION MARKS
NOT OBJECT-ORIENTED
NO SYNTAX CHECKING

25. STACKOVERFLOW

26. STACKOVERFLOW
RAILSCASTS #202

27. STACKOVERFLOW
RAILSCASTS #202
BLOGS

28. STACKOVERFLOW
RAILSCASTS #202
BLOGS
COWORKERS

29. STACKOVERFLOW
RAILSCASTS #202
BLOGS
COWORKERS
FRIENDS

30. STACKOVERFLOW
RAILSCASTS #202
BLOGS
COWORKERS
FRIENDS
FAMILY MEMBERS

31. STACKOVERFLOW
RAILSCASTS #202
BLOGS
COWORKERS
FRIENDS
FAMILY MEMBERS
YOUR CAT

32. KEEP CALM
AND
AVOID
LITERAL
STRINGS IN
YOUR
QUERIES

33. A BETTER WAY
Post
.joins(:comments)
.joins(Comment.joins(:author).join_sources)
.where(
Author[:name].eq("Barack Obama")
.and(Post[:active].eq(true))
)

34. A BETTER WAY
Post
.joins(:comments)
.joins(Comment.joins(:author).join_sources)
.where(
Author[:name].eq("Barack Obama")
.and(Post[:active].eq(true))
)
DON’T HAVE TO KNOW SQL SYNTAX

35. A BETTER WAY
Post
.joins(:comments)
.joins(Comment.joins(:author).join_sources)
.where(
Author[:name].eq("Barack Obama")
.and(Post[:active].eq(true))
)
DON’T HAVE TO KNOW SQL SYNTAX
RUBY SYNTAX CHECKING

36. A BETTER WAY
Post
.joins(:comments)
.joins(Comment.joins(:author).join_sources)
.where(
Author[:name].eq("Barack Obama")
.and(Post[:active].eq(true))
)
DON’T HAVE TO KNOW SQL SYNTAX
RUBY SYNTAX CHECKING
OBJECT-ORIENTED (CHAINABLE)

37. A BETTER WAY
Post
.joins(:comments)
.joins(Comment.joins(:author).join_sources)
.where(
Author[:name].eq("Barack Obama")
.and(Post[:active].eq(true))
)
DON’T HAVE TO KNOW SQL SYNTAX
RUBY SYNTAX CHECKING
OBJECT-ORIENTED (CHAINABLE)
NO QUESTION MARKS

38. A BETTER WAY
Post
.joins(:comments)
.joins(Comment.joins(:author).join_sources)
.where(
Author[:name].eq("Barack Obama")
.and(Post[:active].eq(true))
)
DON’T HAVE TO KNOW SQL SYNTAX
RUBY SYNTAX CHECKING
OBJECT-ORIENTED (CHAINABLE)
NO QUESTION MARKS
EASY TO READ - IT’S JUST RUBY!

39. WHAT WE’LL COVER
ACTIVERECORD VS AREL
TABLES, COLUMNS
TERMINAL METHODS
SELECT, WHERE, JOIN, JOIN ASSOCIATION, ORDER
AND, OR , GREATER/LESS THAN, NOT EQUALS, ETC
MATCH, IN

40. ACTIVERECORD
DATABASE ABSTRACTION
NO NEED TO SPEAK A DIALECT OF SQL
PERSISTENCE
DATABASE ROWS AS RUBY OBJECTS
DOMAIN LOGIC
MODELS CONTAIN APPLICATION LOGIC, VALIDATIONS, ETC
MODELS DEFINE ASSOCIATIONS

41. AREL
“RELATIONAL ALGEBRA” FOR RUBY
BUILDS SQL QUERIES, GENERATES ASTS
APPLIES QUERY OPTIMIZATIONS
ENABLES CHAINING
“VEXINGLY UNDOCUMENTED”

42. AREL
KNOWS NOTHING ABOUT YOUR MODELS
KNOWS VERY LITTLE ABOUT YOUR DATABASE
DOES NOT RETRIEVE OR STORE DATA

43. AREL
KNOWS NOTHING ABOUT YOUR MODELS
KNOWS VERY LITTLE ABOUT YOUR DATABASE
DOES NOT RETRIEVE OR STORE DATA
ACTIVERECORD’S RESPONSIBILITY

44. AREL
CONSTRUCTS QUERIES

45. ACTIVERECORD
DOES EVERYTHING ELSE

46. HIERARCHY
activerecord
arel
database

47. activerecord
arel
database
CONSTRUCT QUERY
EXECUTE QUERY
HIERARCHY

48. WHAT’S AN AST?
7
4 9
1 5

49. WHAT’S AN AST?
7
4 9
1 5
LEFT CHILD

50. WHAT’S AN AST?
7
4 9
1 5
LEFT CHILD RIGHT CHILD

51. WHAT’S AN AST?
5 * (6 + 3)
*
5 +
6 3

52. WHAT’S AN AST?
SELECT id, text FROM posts
SELECT
id text
<query>
FROM
posts

53. LET’S GET TO SOME CODE

54. AREL-HELPERS GEM
gem install arel-helpers
gem “arel-helpers”, “~> 1.1.0”

55. TABLES AND COLUMNS
class Post < ActiveRecord::Base
has_many :comments
end

56. TABLES AND COLUMNS
class Post < ActiveRecord::Base
has_many :comments
end
Post.arel_table[:id]

57. TABLES AND COLUMNS
class Post < ActiveRecord::Base
has_many :comments
end
Post.arel_table[:id]
Post.arel_table[:text]

58. TABLES AND COLUMNS
class Post < ActiveRecord::Base
has_many :comments
end
Post.arel_table[:id]
Post.arel_table[:text]
=> #<struct Arel::Attributes::Attribute ... >

59. TABLES AND COLUMNS
class Post < ActiveRecord::Base
include ArelHelpers::ArelTable
has_many :comments
end
Post.arel_table[:id]
Post.arel_table[:text]
=> #<struct Arel::Attributes::Attribute ... >

60. TABLES AND COLUMNS
class Post < ActiveRecord::Base
include ArelHelpers::ArelTable
has_many :comments
end
Post[:id]
Post[:text]
=> #<struct Arel::Attributes::Attribute ... >

61. RELATIONS
POP QUIZ! WHAT DOES THIS STATEMENT RETURN?
Post.select(:title)

62. RELATIONS
POP QUIZ! WHAT DOES THIS STATEMENT RETURN?
Post.select(:title)
A. [“Rails is Cool” ... ]

63. RELATIONS
POP QUIZ! WHAT DOES THIS STATEMENT RETURN?
Post.select(:title)
A. [“Rails is Cool” ... ]
B. [#<Post title=”Rails is Cool”>, ... ]

64. RELATIONS
POP QUIZ! WHAT DOES THIS STATEMENT RETURN?
Post.select(:title)
A. [“Rails is Cool” ... ]
C. <ActiveRecord::Relation ... >
B. [#<Post title=”Rails is Cool”>, ... ]

65. RELATIONS
POP QUIZ! WHAT DOES THIS STATEMENT RETURN?
Post.select(:title)
A. [“Rails is Cool” ... ]
C. <ActiveRecord::Relation ... >
B. [#<Post title=”Rails is Cool”>, ... ]

66. RELATIONS
query = Post.select(:title)

67. RELATIONS
query = Post.select(:title)
query = query.select(:id)

68. RELATIONS
query = Post.select(:title)
query.to_sql
query = query.select(:id)

69. RELATIONS
query = Post.select(:title)
query.to_sql
=> SELECT title, id FROM `posts`
query = query.select(:id)

70. RELATIONS
query = Post.select(:title)
query.to_sql
=> SELECT title, id FROM `posts`
query = query.select(:id)
RELATIONS CAN BE CHAINED!

71. THE SERENDIPITY OF “SELECT”

72. SELECT
Post.select([:id, :text]).to_sql
=> SELECT id, text FROM `posts`

73. SELECT
Post.select([:id, :text]).to_sql
=> SELECT id, text FROM `posts`
Post.select(:id).count.to_sql
=> NoMethodError: undefined method `to_sql' for 26:Fixnum

74. SELECT
Post.select([:id, :text]).to_sql
=> SELECT id, text FROM `posts`
Post.select(:id).count.to_sql
=> NoMethodError: undefined method `to_sql' for 26:Fixnum
WHAT HAPPENED??

75. SELECT
Post.select([:id, :text]).to_sql
=> SELECT id, text FROM `posts`
Post.select(:id).count.to_sql
=> NoMethodError: undefined method `to_sql' for 26:Fixnum
WHAT HAPPENED??
.count IS A TERMINAL METHOD

76. SELECT
Post.select([Post[:id].count, :text]).to_sql
=> SELECT COUNT(`posts`.`id`), text FROM `posts`

77. TERMINAL METHODS
EXECUTE IMMEDIATELY
DO NOT RETURN AN ActiveRecord::Relation
count
first, last
to_a
pluck
each, map, ETC

78. TERMINAL METHODS
Post.where(title: "Arel is Cool").each do |post|
puts post.text
end

79. TERMINAL METHODS
Post.where(title: "Arel is Cool").each do |post|
puts post.text
end
Post.where(title: "Arel is Cool").each_slice(3)

80. TERMINAL METHODS
Post.where(title: "Arel is Cool").each do |post|
puts post.text
end
Post.where(title: "Arel is Cool").each_slice(3)
BOTH EXECUTE THE QUERY IMMEDIATELY

81. SELECT
Post.select(Post[:visitors].sum).to_sql
=> SELECT SUM(`posts`.`visitors`) AS sum_id FROM `posts`

82. SELECT
Post.select(Post[:visitors].sum.as("visitor_total")).to_sql
=> SELECT SUM(`posts`.`views`) AS visitor_total FROM `posts`

83. SELECT
Post.select(Post[:visitors].sum).to_sql
=> SELECT SUM(`posts`.`visitors`) AS sum_id FROM `posts`
Post.select(Post[:visitors].maximum).to_sql
=> SELECT MAX(`posts`.`visitors`) AS max_id FROM `posts`

84. SELECT
Post.select(Post[:visitors].sum).to_sql
=> SELECT SUM(`posts`.`visitors`) AS sum_id FROM `posts`
Post.select(Post[:visitors].maximum).to_sql
=> SELECT MAX(`posts`.`visitors`) AS max_id FROM `posts`
Post.select(Post[:visitors].minimum).to_sql
=> SELECT MIN(`posts`.`visitors`) AS min_id FROM `posts`

85. SELECT
Post.select(
Arel::Nodes::NamedFunction.new(
"LENGTH", [Post[:text]]
).as("length")
).to_sql
=> SELECT LENGTH(`posts`.`text`) AS length FROM `posts`

86. SELECT
Post.select(
Arel::Nodes::NamedFunction.new(
"LENGTH", [Post[:text]]
).as("length")
).to_sql
=> SELECT LENGTH(`posts`.`text`) AS length FROM `posts`

87. SELECT
Post.select(
Arel::Nodes::NamedFunction.new(
"LENGTH", [Post[:text]]
).as("length")
).to_sql
=> SELECT LENGTH(`posts`.`text`) AS length FROM `posts`
include Arel::Nodes

88. SELECT
Post.select(
NamedFunction.new(
"LENGTH", [Post[:text]]
).as("length")
).to_sql
=> SELECT LENGTH(`posts`.`text`) AS length FROM `posts`
include Arel::Nodes

89. SELECT
Post.select(Arel.star).to_sql
=> SELECT * FROM `posts`

90. SELECT FROM
Post.select(:id).from(Post.select([:id, :text]).ast).to_sql
=> SELECT id FROM SELECT id, text FROM `posts`

91. THE WONDER OF “WHERE”

92. WHERE
Post.where(title: "Arel is Cool").to_sql
=> SELECT `users`.* FROM `users`
WHERE `users`.`title` = 'Arel is Cool'
WITH ACTIVERECORD SUGAR

93. WHERE
Post.where(title: "Arel is Cool").to_sql
=> SELECT `users`.* FROM `users`
WHERE `users`.`title` = 'Arel is Cool'
WITH ACTIVERECORD SUGAR
Post.where(Post[:title].eq("Arel is Cool")).to_sql
=> SELECT `users`.* FROM `users`
WHERE `users`.`title` = 'Arel is Cool'
WITH AREL

94. WHERE
Post.where(Post[:title].not_eq("Arel is Cool")).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`title` != 'Arel is Cool')

95. WHERE
Post.where(Post[:title].not_eq("Arel is Cool")).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`title` != 'Arel is Cool')
Post.where(Post[:title].not_eq(nil)).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`title` IS NOT NULL)

96. WHERE
Post.where(Post[:visitors].gt(250)).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`visitors` > 250)

97. WHERE
Post.where(Post[:visitors].gt(250)).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`visitors` > 250)
Post.where(Post[:visitors].lt(250)).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`visitors` < 250)

98. WHERE
Post.where(Post[:visitors].gteq(250)).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`visitors` >= 250)
Post.where(Post[:visitors].lteq(250)).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (`posts`.`visitors` <= 250)

99. WHERE
Post.where(
Post[:title].eq("Arel is Cool").and(
Post[:id].eq(22).or(
Post[:id].eq(23)
)
)
).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (
`posts`.`title` = 'Arel is Cool' AND
(`posts`.`id` = 22 OR `posts`.`id` = 23)
)

100. WHERE
Post.where(
Post[:title].eq("Arel is Cool").and(
Post[:id].in(22, 23)
)
).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (
`posts`.`title` = 'Arel is Cool' AND
`posts`.`id` IN (22, 23)
)

101. WHERE
Post.where(
Post[:title].eq("Arel is Cool").and(
NamedFunction.new("LENGTH", [Post[:slug]]).gt(10)
)
).to_sql
=> SELECT `posts`.* FROM `posts`
WHERE (
`posts`.`title` = 'Arel is Cool' AND
LENGTH(`posts`.`slug`) > 10
)

102. THE JOY OF “JOIN”

103. JOIN
class Post < ActiveRecord::Base
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :post
has_one :author
end
class Author < ActiveRecord::Base
belongs_to :comment
end

104. JOIN
Author.joins(:comment).where(id: 42).to_sql
=> SELECT `authors`.* FROM `authors`
INNER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
WHERE `authors`.`id` = 42

105. JOIN
Author
.joins(:comment, :comment => :post)
.where(Post[:id].eq(42))
.to_sql
=> SELECT `authors`.* FROM `authors`
INNER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
INNER JOIN `posts`
ON `posts`.`id` = `comments`.`post_id`
WHERE `posts`.`id` = 42

106. WAIT, WHAT ABOUT OUTER JOINS?

107. JOIN
Author
.joins(:comment, :comment => :post)
.where(Post[:id].eq(42))
.to_sql
=> SELECT `authors`.* FROM `authors`
INNER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
INNER JOIN `posts`
ON `posts`.`id` = `comments`.`post_id`
WHERE `posts`.`id` = 42

108. JOIN
Author
.joins(:comment)
.joins(Comment.joins(:post).join_sources)
.where(Post[:id].eq(42))
.to_sql
=> SELECT `authors`.* FROM `authors`
INNER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
INNER JOIN `posts`
ON `posts`.`id` = `comments`.`post_id`
WHERE `posts`.`id` = 42

109. JOIN
Author
.joins(Author.joins(:comment).join_sources)
.joins(Comment.joins(:post).join_sources)
.where(Post[:id].eq(42))
.to_sql
=> SELECT `authors`.* FROM `authors`
INNER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
INNER JOIN `posts`
ON `posts`.`id` = `comments`.`post_id`
WHERE `posts`.`id` = 42

110. JOIN
Author
.joins(
Author.arel_table.join(Comment.arel_table)
.on(Comment[:id].eq(Author[:comment_id]))
.join_sources
)
.joins(
Comment.arel_table.join(Post.arel_table)
.on(Post[:id].eq(Comment[:post_id]))
.join_sources
)
.where(Post[:id].eq(42))
.to_sql

111. JOIN
Author
.joins(
Author.arel_table.join(Comment.arel_table, Arel::OuterJoin)
.on(Comment[:id].eq(Author[:comment_id]))
.join_sources
)
.joins(
Comment.arel_table.join(Post.arel_table, Arel::OuterJoin)
.on(Post[:id].eq(Comment[:post_id]))
.join_sources
)
.where(Post[:id].eq(42))
.to_sql

112. JOIN
=> SELECT `authors`.* FROM `authors`
LEFT OUTER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
LEFT OUTER JOIN `posts`
ON `posts`.`id` = `comments`.`post_id`
WHERE `posts`.`id` = 42

114. JOIN
Author
.joins(
Author.arel_table.join(Comment.arel_table, Arel::OuterJoin)
.on(Comment[:id].eq(Author[:comment_id]))
.join_sources
)
.joins(
Comment.arel_table.join(Post.arel_table, Arel::OuterJoin)
.on(Post[:id].eq(Comment[:post_id]))
.join_sources
)
.where(Post[:id].eq(42))
.to_sql

115. JOIN
Author
.joins(
Author.arel_table.join(Comment.arel_table, Arel::OuterJoin)
.on(Comment[:id].eq(Author[:comment_id]))
.join_sources
)
.joins(
Comment.arel_table.join(Post.arel_table, Arel::OuterJoin)
.on(Post[:id].eq(Comment[:post_id]))
.join_sources
)
.where(Post[:id].eq(42))
.to_sql

116. JOIN
Author
.joins(
Author.arel_table.join(Comment.arel_table, Arel::OuterJoin)
.on(Comment[:id].eq(Author[:comment_id]))
.join_sources
)
.joins(
Comment.arel_table.join(Post.arel_table, Arel::OuterJoin)
.on(Post[:id].eq(Comment[:post_id]))
.join_sources
)
.where(Post[:id].eq(42))
.to_sql
include ArelHelpers::JoinAssociation

117. JOIN
Author
.joins(join_association(Author, :comment, Arel::OuterJoin))
.joins(
Comment.arel_table.join(Post.arel_table, Arel::OuterJoin)
.on(Post[:id].eq(Comment[:post_id]))
.join_sources
)
.where(Post[:id].eq(42))
.to_sql
include ArelHelpers::JoinAssociation

118. JOIN
Author
.joins(join_association(Author, :comment, Arel::OuterJoin))
.joins(join_association(Comment, :post, Arel::OuterJoin))
.where(Post[:id].eq(42))
.to_sql
include ArelHelpers::JoinAssociation

120. JOIN
Author
.joins(
join_association(Author, :comment) do |assoc_name, join_conds|
join_conds.and(Comment[:created_at].lteq(Date.yesterday))
end
)
.joins(join_association(Comment, :post, Arel::OuterJoin))
.where(Post[:id].eq(42))
.to_sql
include ArelHelpers::JoinAssociation

121. JOIN
=> SELECT `authors`.* FROM `authors`
INNER JOIN `comments`
ON `comments`.`id` = `authors`.`comment_id`
AND `comments`.`created_at` <= '2014-04-15'
LEFT OUTER JOIN `posts`
ON `posts`.`id` = `comments`.`post_id`
WHERE `posts`.`id` = 42

122. JOIN TABLES
class Course < ActiveRecord::Base
has_and_belongs_to_many :teachers
end
class Teacher < ActiveRecord::Base
has_and_belongs_to_many :courses
end

123. JOIN TABLES
class Course < ActiveRecord::Base
has_and_belongs_to_many :teachers
end
class Teacher < ActiveRecord::Base
has_and_belongs_to_many :courses
end
courses
teachers
courses_teachers

124. JOIN TABLES

125. JOIN TABLES
course TABLE

126. JOIN TABLES
Course.arel_table
course TABLE

127. JOIN TABLES
Course.arel_table
course TABLE
teacher TABLE

128. JOIN TABLES
Course.arel_table
Teacher.arel_table
course TABLE
teacher TABLE

129. JOIN TABLES
Course.arel_table
Teacher.arel_table
course TABLE
teacher TABLE
courses_teachers TABLE

130. JOIN TABLES
Course.arel_table
Teacher.arel_table
course TABLE
teacher TABLE
???? (no model class)
courses_teachers TABLE

131. JOIN TABLES

132. JOIN TABLES
ct = Arel::Table.new(:courses_teachers)

133. JOIN TABLES
ct = Arel::Table.new(:courses_teachers)
Course
.joins(
Course.arel_table.join(Teacher.arel_table)
.on(Course[:id].eq(ct[:course_id]))
.and(Teacher[:id].eq(ct[:teacher_id]))
.join_sources
)
.to_sql

134. THE OPULENCE OF “ORDER”

135. ORDER
Post.order(:visitors).to_sql
=> SELECT `posts`.* FROM `posts` ORDER BY visitors

136. ORDER
Post.order(:visitors).to_sql
=> SELECT `posts`.* FROM `posts` ORDER BY visitors
Post.order(:views).reverse_order.to_sql
=> SELECT `posts`.* FROM `posts` ORDER BY visitors DESC

137. ORDER
Post.order(:visitors).to_sql
=> SELECT `posts`.* FROM `posts` ORDER BY visitors
Post.order(:views).reverse_order.to_sql
=> SELECT `posts`.* FROM `posts` ORDER BY visitors DESC
Post.order(Post[:views].desc).to_sql
=> SELECT `posts`.* FROM `posts` ORDER BY visitors DESC

138. SUBQUERIES WITH “IN”

139. IN
Post.where(
Post.arel_table[:title].in(
Post.select(:title).where(id: 5).ast
)
).to_sql
=> SELECT `phrases`.* FROM `phrases`
WHERE `phrases`.`title` IN (
SELECT title FROM `phrases` WHERE `phrases`.`id` = 5
)

140. LIKE QUERIES WITH “MATCHES”

141. MATCHES
Post.where(Post[:title].matches("%arel%")).to_sql
=> SELECT `phrases`.* FROM `phrases`
WHERE (`phrases`.`key` LIKE x'256172656c25')

142. QUERY BUILDERS

143. class QueryBuilder
extend Forwardable
attr_reader :query
def_delegators :@query, :to_a, :to_sql, :each
def initialize(query)
@query = query
end
protected
def reflect(query)
self.class.new(query)
end
end

144. class PostQueryBuilder < QueryBuilder
def initialize(query = nil)
super(query || post.unscoped)
end
def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end
def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end
def since_yesterday
reflect(
query.where(post[:created_at].gteq(Date.yesterday))
)
end
private
def author
Author
end
def post
Post
end
end

145. class PostQueryBuilder < QueryBuilder
def initialize(query = nil)
super(query || post.unscoped)
end
def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end
def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end
def since_yesterday
reflect(
query.where(post[:created_at].gteq(Date.yesterday))
)
end
private
def author
Author
end
def post
Post
end
end

146. def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end

147. class PostQueryBuilder < QueryBuilder
def initialize(query = nil)
super(query || post.unscoped)
end
def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end
def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end
def since_yesterday
reflect(
query.where(post[:created_at].gteq(Date.yesterday))
)
end
private
def author
Author
end
def post
Post
end
end

148. class PostQueryBuilder < QueryBuilder
def initialize(query = nil)
super(query || post.unscoped)
end
def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end
def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end
def since_yesterday
reflect(
query.where(post[:created_at].gteq(Date.yesterday))
)
end
private
def author
Author
end
def post
Post
end
end

149. def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end

150. class PostQueryBuilder < QueryBuilder
def initialize(query = nil)
super(query || post.unscoped)
end
def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end
def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end
def since_yesterday
reflect(
query.where(post[:created_at].gteq(Date.yesterday))
)
end
private
def author
Author
end
def post
Post
end
end

151. class PostQueryBuilder < QueryBuilder
def initialize(query = nil)
super(query || post.unscoped)
end
def with_title_matching(title)
reflect(
query.where(post[:title].matches("%#{title}%"))
)
end
def with_comments_by(usernames)
reflect(
query
.joins(:comments => :author)
.where(Author[:username].in(usernames))
)
end
def since_yesterday
reflect(
query.where(post[:created_at].gteq(Date.yesterday))
)
end
private
def author
Author
end
def post
Post
end
end

152. def since_yesterday
reflect(
query.where(
post[:created_at].gteq(Date.yesterday)
)
)
end

153. EXAMPLES
PostQueryBuilder.new
.with_comments_by(['camertron', 'catwithtail'])
.to_sql
=> SELECT `posts`.* FROM `posts`
INNER JOIN `comments`
ON `comments`.`post_id` = `posts`.`id`
INNER JOIN `authors`
ON `authors`.`comment_id` = `comments`.`id`
WHERE `authors`.`username` IN (
'camertron', 'catwithtail'
)

154. EXAMPLES
PostQueryBuilder.new
.with_comments_by(['camertron', 'catwithtail'])
.with_title_matching("arel").to_sql
=> SELECT `posts`.* FROM `posts`
INNER JOIN `comments`
ON `comments`.`post_id` = `posts`.`id`
INNER JOIN `authors`
ON `authors`.`comment_id` = `comments`.`id`
WHERE `authors`.`username` IN (
'camertron', 'catwithtail'
) AND (`posts`.`title` LIKE '%arel%')

155. EXAMPLES
PostQueryBuilder.new
.with_comments_by(['camertron', 'catwithtail'])
.with_title_matching(`arel`).since_yesterday.to_sql
=> SELECT `posts`.* FROM `posts`
INNER JOIN `comments`
ON `comments`.`post_id` = `posts`.`id`
INNER JOIN `authors`
ON `authors`.`comment_id` = `comments`.`id`
WHERE `authors`.`username` IN (
'camertron', 'catwithtail'
) AND (`posts`.`title` LIKE '%arel%')
AND (`posts`.`created_at` >= '2014-04-20')

156. Sigh... this is all so complicated.
Surely there’s a tool out there...“
”

157. SCUTTLE
www.scuttle.io

159. SCUTTLE
sql-parser (java)
http://github.com/camertron/sql-parser
scuttle-rb (jRuby gem)
http://github.com/camertron/scuttle-rb
scuttle-server (sinatra jRuby)
http://github.com/camertron/scuttle-server

160. THANK YOU!