Open a database
require 'rubygems'
require 'sequel'
DB = Sequel.sqlite('my_blog.db')
DB = Sequel.connect('postgres://user:password@localhost/my_db')
DB = Sequel.postgres('my_db', :user => 'user', :password => 'password', :host => 'localhost')
DB = Sequel.ado('mydb')
Open an SQLite memory database
Without a filename argument, the sqlite adapter will setup a new sqlite database in memory.
DB = Sequel.sqlite
Logging SQL statements
require 'logger'
DB = Sequel.sqlite '', :loggers => [Logger.new($stdout)]
# or
DB.loggers << Logger.new(...)
Using raw SQL
DB.run "CREATE TABLE users (name VARCHAR(255) NOT NULL, age INT(3) NOT NULL)"
dataset = DB["SELECT age FROM users WHERE name = ?", name]
dataset.map(:age)
DB.fetch("SELECT name FROM users") do |row|
p row[:name]
end
Create a dataset
dataset = DB[:items]
dataset = DB.from(:items)
Most dataset methods are chainable
dataset = DB[:managers].where(:salary => 5000..10000).order(:name, :department)
Insert rows
dataset.insert(:name => 'Sharon', :grade => 50)
Retrieve rows
dataset.each{|r| p r}
dataset.all # => [{...}, {...}, ...]
dataset.first # => {...}
Update/Delete rows
dataset.filter(~:active).delete
dataset.filter('price < ?', 100).update(:active => true)
Datasets are Enumerable
dataset.map{|r| r[:name]}
dataset.map(:name) # same as above
dataset.inject(0){|sum, r| sum + r[:value]}
dataset.sum(:value) # same as above
Filtering (see also doc/dataset_filtering.rdoc)
Equality
dataset.filter(:name => 'abc')
dataset.filter('name = ?', 'abc')
Inequality
dataset.filter{value > 100}
dataset.exclude{value <= 100}
Inclusion
dataset.filter(:value => 50..100)
dataset.where{(value >= 50) & (value <= 100)}
dataset.where('value IN ?', [50,75,100])
dataset.where(:value=>[50,75,100])
dataset.where(:id=>other_dataset.select(:other_id))
Subselects as scalar values
dataset.where('price > (SELECT avg(price) + 100 FROM table)')
dataset.filter{price > dataset.select(avg(price) + 100)}
LIKE/Regexp
DB[:items].filter(:name.like('AL%'))
DB[:items].filter(:name => /^AL/)
AND/OR/NOT
DB[:items].filter{(x > 5) & (y > 10)}.sql
# SELECT * FROM items WHERE ((x > 5) AND (y > 10))
DB[:items].filter({:x => 1, :y => 2}.sql_or & ~{:z => 3}).sql
# SELECT * FROM items WHERE (((x = 1) OR (y = 2)) AND (z != 3))
Mathematical operators
DB[:items].filter((:x + :y) > :z).sql
# SELECT * FROM items WHERE ((x + y) > z)
DB[:items].filter{price - 100 < avg(price)}.sql
# SELECT * FROM items WHERE ((price - 100) < avg(price))
Ordering
dataset.order(:kind)
dataset.reverse_order(:kind)
dataset.order(:kind.desc, :name)
Limit/Offset
dataset.limit(30) # LIMIT 30
dataset.limit(30, 10) # LIMIT 30 OFFSET 10
Joins
DB[:items].left_outer_join(:categories, :id => :category_id).sql
# SELECT * FROM items LEFT OUTER JOIN categories ON categories.id = items.category_id
DB[:items].join(:categories, :id => :category_id).join(:groups, :id => :items__group_id)
# SELECT * FROM items INNER JOIN categories ON categories.id = items.category_id INNER JOIN groups ON groups.id = items.group_id
Aggregate functions methods
dataset.count #=> record count
dataset.max(:price)
dataset.min(:price)
dataset.avg(:price)
dataset.sum(:stock)
dataset.group_and_count(:category)
dataset.group(:category).select(:category, :AVG.sql_function(:price))
SQL Functions / Literals
dataset.update(:updated_at => :NOW.sql_function)
dataset.update(:updated_at => 'NOW()'.lit)
dataset.update(:updated_at => "DateValue('1/1/2001')".lit)
dataset.update(:updated_at => :DateValue.sql_function('1/1/2001'))
Schema Manipulation
DB.create_table :items do
primary_key :id
String :name, :unique => true, :null => false
TrueClass :active, :default => true
foreign_key :category_id, :categories
DateTime :created_at
index :created_at
end
DB.drop_table :items
DB.create_table :test do
String :zipcode
enum :system, :elements => ['mac', 'linux', 'windows']
end
Aliasing
DB[:items].select(:name.as(:item_name))
DB[:items].select(:name___item_name)
DB[:items___items_table].select(:items_table__name___item_name)
# SELECT items_table.name AS item_name FROM items AS items_table
Transactions
DB.transaction do
dataset.insert(:first_name => 'Inigo', :last_name => 'Montoya')
dataset.insert(:first_name => 'Farm', :last_name => 'Boy')
end # Either both are inserted or neither are inserted
Database#transaction is re-entrant:
DB.transaction do # BEGIN issued only here
DB.transaction
dataset << {:first_name => 'Inigo', :last_name => 'Montoya'}
end
end # COMMIT issued only here
Transactions are aborted if an error is raised:
DB.transaction do
raise "some error occurred"
end # ROLLBACK issued and the error is re-raised
Transactions can also be aborted by raising Sequel::Rollback:
DB.transaction do
raise(Sequel::Rollback) if something_bad_happened
end # ROLLBACK issued and no error raised
Savepoints can be used if the database supports it:
DB.transaction do
dataset << {:first_name => 'Farm', :last_name => 'Boy'} # Inserted
DB.transaction(:savepoint=>true) # This savepoint is rolled back
dataset << {:first_name => 'Inigo', :last_name => 'Montoya'} # Not inserted
raise(Sequel::Rollback) if something_bad_happened
end
dataset << {:first_name => 'Prince', :last_name => 'Humperdink'} # Inserted
end
Miscellaneous:
dataset.sql # "SELECT * FROM items"
dataset.delete_sql # "DELETE FROM items"
dataset.where(:name => 'sequel').exists # "EXISTS ( SELECT * FROM items WHERE name = 'sequel' )"
dataset.columns #=> array of columns in the result set, does a SELECT
DB.schema(:items) => [[:id, {:type=>:integer, ...}], [:name, {:type=>:string, ...}], ...]
Documents
http://sequel.rubyforge.org/rdoc/files/doc/association_basics_rdoc.html
http://sequel.rubyforge.org/rdoc/classes/Sequel/Schema/Generator.html
http://sequel.rubyforge.org/rdoc/files/doc/validations_rdoc.html
http://sequel.rubyforge.org/rdoc/classes/Sequel/Model.html
Alter table
database.alter_table :deals do
add_column :name, String
drop_column :column_name
rename_column :from, :to
add_constraint :valid_name, :name.like('A%')
drop_constraint :constraint
add_full_text_index :body
add_spacial_index [columns]
add_index :price
drop_index :index
add_foreign_key :artist_id, :table
add_primary_key :id
add_unique_constraint [columns]
set_column_allow_null :foo, false
set_column_default :title, ''
set_column_type :price, 'char(10)'
end
Model associations
class Deal < Sequel::Model
# Us (left) <=> Them (right)
many_to_many :images,
left_id: :deal_id,
right_id: :image_id,
join_table: :image_links
one_to_many :files,
key: :deal_id,
class: :DataFile,
many_to_one :parent, class: self
one_to_many :children, key: :parent_id, class: self
one_to_many :gold_albums, class: :Album do |ds|
ds.filter { copies_sold > 50000 }
end
Provided by many_to_many
Deal[1].images
Deal[1].add_image
Deal[1].remove_image
Deal[1].remove_all_images
Validations
def validate
super
errors.add(:name, 'cannot be empty') if !name || name.empty?
validates_presence [:title, :site]
validates_unique :name
validates_format /\Ahttps?:\/\//, :website, :message=>'is not a valid URL'
validates_includes %w(a b c), :type
validates_integer :rating
validates_numeric :number
validates_type String, [:title, :description]
validates_integer :rating if new?
# options: :message =>, :allow_nil =>, :allow_blank =>,
# :allow_missing =>,
validates_exact_length 17, :isbn
validates_min_length 3, :name
validates_max_length 100, :name
validates_length_range 3..100, :name
# Setter override
def filename=(name)
@values[:filename] = name
end
end
end
deal.errors
Model stuff
deal = Deal[1]
deal.changed_columns
deal.destroy # Calls hooks
deal.delete # No hooks
deal.exists?
deal.new?
deal.hash # Only uniques
deal.keys #=> [:id, :name]
deal.modified!
deal.modified?
deal.lock!
Callbacks
before_create
after_create
before_validation
after_validation
before_save
before_update
UPDATE QUERY
after_update
after_save
before_destroy
DELETE QUERY
after_destroy
Schema
class Deal < Sequel::Model
set_schema do
primary_key :id
primary_key [:id, :title]
String :name, primary_key: true
String :title
Numeric :price
DateTime :expires
unique :whatever
check(:price) { num > 0 }
foreign_key :artist_id
String :artist_name, key: :id
index :title
index [:artist_id, :name]
full_text_index :title
# String, Integer, Fixnum, Bignum, Float, Numeric, BigDecimal,
# Date, DateTime, Time, File, TrueClass, FalseClass
end
end
Unrestrict primary key
Category.create id: 'travel' # error
Category.unrestrict_primary_key
Category.create id: 'travel' # ok
