| Path: | doc/cheat_sheet.rdoc |
| Last Update: | Wed Feb 25 03:52:27 -0700 2009 |
require 'rubygems'
require 'sequel'
DB = Sequel.sqlite('my_blog.db')
DB = Sequel.connect('postgres://user:password@localhost/my_db')
DB = Sequel.mysql('my_db', :user => 'user', :password => 'password', :host => 'localhost')
DB = Sequel.ado('mydb')
Without a filename argument, the sqlite adapter will setup a new sqlite database in RAM.
DB = Sequel.sqlite
require 'logger' DB = Sequel.sqlite '', :loggers => [Logger.new($stdout)] # or DB.loggers << Logger.new(...)
DB << "CREATE TABLE users (name VARCHAR(255) NOT NULL, age INT(3) NOT NULL)"
DB.fetch("SELECT name FROM users") do |row|
p r[:name]
end
dataset = DB["SELECT age FROM users WHERE name = ?", name]
dataset.print
dataset.map(:age)
dataset = DB[:items] dataset = DB.dataset.from(:items)
dataset = DB[:managers].where(:salary => 5000..10000).order(:name, :department)
# or
dataset = DB.query do
from :managers
where :salary => 5000..10000
order :name, :department
end
dataset.insert(:name => 'Sharon', :grade => 50)
dataset << {:name => 'Sharon', :grade => 50} # same effect as above
dataset.each {|r| p r}
dataset.all #=> [{...}, {...}, ...]
dataset.first
dataset.order(:name).last # works only for ordered datasets
dataset.filter(:active => false).delete
dataset.filter('price < ?', 100).update(:active => true)
dataset.map {|r| r[:name]}
dataset.map(:name) # same effect as above
dataset.inject(0){|sum, r| sum + r[:value]}
dataset.filter(:name => 'abc')
dataset.filter('name = ?', 'abc')
dataset.filter{|o| o.value > 100}
dataset.exclude{|o| o.value <= 100}
dataset.filter(:value => 50..100)
dataset.where{|o| (o.value >= 50) & (o.value <= 100)}
dataset.where('value IN ?', [50,75,100])
# Get the first record that matches a condition
dataset[:name => 'abc'] # Same as:
dataset.filter(:name => 'abc').first
# Filter using a subquery
dataset.filter('price > ?', dataset.select('AVG(price) + 100'))
DB[:items].filter{|o| o.price < 100}.sql
#=> "SELECT * FROM items WHERE (price < 100)"
DB[:items].filter(:name.like('AL%')).sql
#=> "SELECT * FROM items WHERE (name LIKE 'AL%')"
There‘s support for nested expressions with AND, OR and NOT:
DB[:items].filter{|o| (o.x > 5) & (o.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))"
You can use arithmetic operators and specify SQL functions:
DB[:items].filter((:x + :y) > :z).sql
#=> "SELECT * FROM items WHERE ((x + y) > z)"
DB[:items].filter{|o| :price - 100 < o.AVG(:price)}.sql
#=> "SELECT * FROM items WHERE ((price - 100) < AVG(price))"
dataset.order(:kind) dataset.reverse_order(:kind) dataset.order(:kind.desc, :name)
dataset.limit(30) # LIMIT 30 dataset.limit(30, 10) # LIMIT 30 OFFSET 10
paginated = dataset.paginate(1, 10) # first page, 10 rows per page paginated.page_count #=> number of pages in dataset paginated.current_page #=> 1 paginated.next_page #=> next page number or nil paginated.prev_page #=> previous page number or nil paginated.first_page? #=> true if page number = 1 paginated.last_page? #=> true if page number = page_count
DB[:items].left_outer_join(:categories, :id => :category_id).sql #=>
"SELECT * FROM items LEFT OUTER JOIN categories ON categories.id = items.category_id"
dataset.count #=> record count dataset.max(:price) dataset.min(:price) dataset.avg(:price) dataset.sum(:stock) dataset.group(:category).select(:category, :AVG.sql_function(:price))
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'))
DB.create_table :items do
primary_key :id
String :name, :unique => true, :null => false
boolean :active, :default => true
foreign_key :category_id, :categories
Time :created_at
index :grade
end
DB.drop_table :items
DB.create_table :test do
String :zipcode, :size => 10
enum :system, :elements => ['mac', 'linux', 'windows']
end
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"
DB.transaction do
dataset << {:first_name => 'Inigo', :last_name => 'Montoya'}
dataset << {: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::Error::Rollback:
DB.transaction do
raise(Sequel::Error::Rollback) if something_bad_happened
end # ROLLBACK issued and no error raised
Miscellaneous:
dataset.sql #=> "SELECT * FROM items"
dataset.delete_sql #=> "DELETE FROM items"
dataset.where(:name => 'sequel').exists #=> "EXISTS ( SELECT 1 FROM items WHERE name = 'sequel' )"
dataset.print #=> pretty table print to $stdout
dataset.columns #=> array of columns in the result set, does a SELECT
DB.schema(:items) => [[:id, {:type=>:integer, ...}], [:name, {:type=>:string, ...}], ...]
# Works on PostgreSQL, MySQL, SQLite, and JDBC