629 lines
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629 lines
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This is <a href="."><em>Devhints.io cheatsheets</em></a> — a collection of cheatsheets I've written.
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<div class='post-headline -cheatsheet'>
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<p class='prelude'><span></span></p>
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<h1><span>Sequel</span></h1>
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<h3 id="open-a-database">Open a database</h3>
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<pre><code>require 'rubygems'
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require 'sequel'
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DB = Sequel.sqlite('my_blog.db')
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DB = Sequel.connect('postgres://user:password@localhost/my_db')
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DB = Sequel.postgres('my_db', :user => 'user', :password => 'password', :host => 'localhost')
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DB = Sequel.ado('mydb')
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</code></pre>
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<h3 id="open-an-sqlite-memory-database">Open an SQLite memory database</h3>
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<p>Without a filename argument, the sqlite adapter will setup a new sqlite database in memory.</p>
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<pre><code>DB = Sequel.sqlite
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</code></pre>
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<h3 id="logging-sql-statements">Logging SQL statements</h3>
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<pre><code>require 'logger'
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DB = Sequel.sqlite '', :loggers => [Logger.new($stdout)]
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# or
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DB.loggers << Logger.new(...)
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</code></pre>
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<h3 id="using-raw-sql">Using raw SQL</h3>
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<pre><code>DB.run "CREATE TABLE users (name VARCHAR(255) NOT NULL, age INT(3) NOT NULL)"
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dataset = DB["SELECT age FROM users WHERE name = ?", name]
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dataset.map(:age)
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DB.fetch("SELECT name FROM users") do |row|
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p row[:name]
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end
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</code></pre>
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<h3 id="create-a-dataset">Create a dataset</h3>
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<pre><code>dataset = DB[:items]
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dataset = DB.from(:items)
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</code></pre>
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<h3 id="most-dataset-methods-are-chainable">Most dataset methods are chainable</h3>
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<pre><code>dataset = DB[:managers].where(:salary => 5000..10000).order(:name, :department)
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</code></pre>
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<h3 id="insert-rows">Insert rows</h3>
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<pre><code>dataset.insert(:name => 'Sharon', :grade => 50)
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</code></pre>
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<h3 id="retrieve-rows">Retrieve rows</h3>
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<pre><code>dataset.each{|r| p r}
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dataset.all # => [{...}, {...}, ...]
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dataset.first # => {...}
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</code></pre>
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<h3 id="updatedelete-rows">Update/Delete rows</h3>
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<pre><code>dataset.filter(~:active).delete
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dataset.filter('price < ?', 100).update(:active => true)
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</code></pre>
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<h3 id="datasets-are-enumerable">Datasets are Enumerable</h3>
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<pre><code>dataset.map{|r| r[:name]}
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dataset.map(:name) # same as above
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dataset.inject(0){|sum, r| sum + r[:value]}
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dataset.sum(:value) # same as above
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</code></pre>
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<h3 id="filtering-see-also-docdataset_filteringrdoc">Filtering (see also doc/dataset_filtering.rdoc)</h3>
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<h4 id="equality">Equality</h4>
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<pre><code>dataset.filter(:name => 'abc')
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dataset.filter('name = ?', 'abc')
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</code></pre>
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<h4 id="inequality">Inequality</h4>
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<pre><code>dataset.filter{value > 100}
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dataset.exclude{value <= 100}
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</code></pre>
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<h4 id="inclusion">Inclusion</h4>
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<pre><code>dataset.filter(:value => 50..100)
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dataset.where{(value >= 50) & (value <= 100)}
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dataset.where('value IN ?', [50,75,100])
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dataset.where(:value=>[50,75,100])
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dataset.where(:id=>other_dataset.select(:other_id))
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</code></pre>
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<h4 id="subselects-as-scalar-values">Subselects as scalar values</h4>
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<pre><code>dataset.where('price > (SELECT avg(price) + 100 FROM table)')
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dataset.filter{price > dataset.select(avg(price) + 100)}
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</code></pre>
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<h4 id="likeregexp">LIKE/Regexp</h4>
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<pre><code>DB[:items].filter(:name.like('AL%'))
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DB[:items].filter(:name => /^AL/)
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</code></pre>
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<h4 id="andornot">AND/OR/NOT</h4>
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<pre><code>DB[:items].filter{(x > 5) & (y > 10)}.sql
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# SELECT * FROM items WHERE ((x > 5) AND (y > 10))
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DB[:items].filter({:x => 1, :y => 2}.sql_or & ~{:z => 3}).sql
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# SELECT * FROM items WHERE (((x = 1) OR (y = 2)) AND (z != 3))
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</code></pre>
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<h4 id="mathematical-operators">Mathematical operators</h4>
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<pre><code>DB[:items].filter((:x + :y) > :z).sql
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# SELECT * FROM items WHERE ((x + y) > z)
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DB[:items].filter{price - 100 < avg(price)}.sql
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# SELECT * FROM items WHERE ((price - 100) < avg(price))
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</code></pre>
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<h3 id="ordering">Ordering</h3>
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<pre><code>dataset.order(:kind)
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dataset.reverse_order(:kind)
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dataset.order(:kind.desc, :name)
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</code></pre>
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<h3 id="limitoffset">Limit/Offset</h3>
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<pre><code>dataset.limit(30) # LIMIT 30
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dataset.limit(30, 10) # LIMIT 30 OFFSET 10
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</code></pre>
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<h3 id="joins">Joins</h3>
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<pre><code>DB[:items].left_outer_join(:categories, :id => :category_id).sql
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# SELECT * FROM items LEFT OUTER JOIN categories ON categories.id = items.category_id
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DB[:items].join(:categories, :id => :category_id).join(:groups, :id => :items__group_id)
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# SELECT * FROM items INNER JOIN categories ON categories.id = items.category_id INNER JOIN groups ON groups.id = items.group_id
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</code></pre>
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<h3 id="aggregate-functions-methods">Aggregate functions methods</h3>
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<pre><code>dataset.count #=> record count
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dataset.max(:price)
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dataset.min(:price)
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dataset.avg(:price)
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dataset.sum(:stock)
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dataset.group_and_count(:category)
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dataset.group(:category).select(:category, :AVG.sql_function(:price))
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</code></pre>
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<h3 id="sql-functions--literals">SQL Functions / Literals</h3>
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<pre><code>dataset.update(:updated_at => :NOW.sql_function)
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dataset.update(:updated_at => 'NOW()'.lit)
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dataset.update(:updated_at => "DateValue('1/1/2001')".lit)
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dataset.update(:updated_at => :DateValue.sql_function('1/1/2001'))
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</code></pre>
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<h3 id="schema-manipulation">Schema Manipulation</h3>
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<pre><code>DB.create_table :items do
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primary_key :id
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String :name, :unique => true, :null => false
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TrueClass :active, :default => true
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foreign_key :category_id, :categories
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DateTime :created_at
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index :created_at
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end
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DB.drop_table :items
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DB.create_table :test do
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String :zipcode
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enum :system, :elements => ['mac', 'linux', 'windows']
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end
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</code></pre>
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<h3 id="aliasing">Aliasing</h3>
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<pre><code>DB[:items].select(:name.as(:item_name))
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DB[:items].select(:name___item_name)
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DB[:items___items_table].select(:items_table__name___item_name)
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# SELECT items_table.name AS item_name FROM items AS items_table
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</code></pre>
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<h3 id="transactions">Transactions</h3>
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<pre><code>DB.transaction do
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dataset.insert(:first_name => 'Inigo', :last_name => 'Montoya')
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dataset.insert(:first_name => 'Farm', :last_name => 'Boy')
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end # Either both are inserted or neither are inserted
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</code></pre>
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<p>Database#transaction is re-entrant:</p>
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<pre><code>DB.transaction do # BEGIN issued only here
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DB.transaction
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dataset << {:first_name => 'Inigo', :last_name => 'Montoya'}
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end
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end # COMMIT issued only here
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</code></pre>
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<p>Transactions are aborted if an error is raised:</p>
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<pre><code>DB.transaction do
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raise "some error occurred"
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end # ROLLBACK issued and the error is re-raised
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</code></pre>
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<p>Transactions can also be aborted by raising Sequel::Rollback:</p>
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<pre><code>DB.transaction do
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raise(Sequel::Rollback) if something_bad_happened
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end # ROLLBACK issued and no error raised
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</code></pre>
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<p>Savepoints can be used if the database supports it:</p>
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<pre><code>DB.transaction do
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dataset << {:first_name => 'Farm', :last_name => 'Boy'} # Inserted
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DB.transaction(:savepoint=>true) # This savepoint is rolled back
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dataset << {:first_name => 'Inigo', :last_name => 'Montoya'} # Not inserted
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raise(Sequel::Rollback) if something_bad_happened
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end
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dataset << {:first_name => 'Prince', :last_name => 'Humperdink'} # Inserted
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end
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</code></pre>
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<h3 id="miscellaneous">Miscellaneous:</h3>
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<pre><code>dataset.sql # "SELECT * FROM items"
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dataset.delete_sql # "DELETE FROM items"
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dataset.where(:name => 'sequel').exists # "EXISTS ( SELECT * FROM items WHERE name = 'sequel' )"
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dataset.columns #=> array of columns in the result set, does a SELECT
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DB.schema(:items) => [[:id, {:type=>:integer, ...}], [:name, {:type=>:string, ...}], ...]
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</code></pre>
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<hr />
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<h3 id="documents">Documents</h3>
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<pre><code>http://sequel.rubyforge.org/rdoc/files/doc/association_basics_rdoc.html
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http://sequel.rubyforge.org/rdoc/classes/Sequel/Schema/Generator.html
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http://sequel.rubyforge.org/rdoc/files/doc/validations_rdoc.html
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http://sequel.rubyforge.org/rdoc/classes/Sequel/Model.html
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</code></pre>
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<h3 id="alter-table">Alter table</h3>
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<pre><code>database.alter_table :deals do
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add_column :name, String
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drop_column :column_name
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rename_column :from, :to
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add_constraint :valid_name, :name.like('A%')
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drop_constraint :constraint
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add_full_text_index :body
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add_spacial_index [columns]
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add_index :price
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drop_index :index
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add_foreign_key :artist_id, :table
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add_primary_key :id
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add_unique_constraint [columns]
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set_column_allow_null :foo, false
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set_column_default :title, ''
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set_column_type :price, 'char(10)'
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end
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</code></pre>
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<h3 id="model-associations">Model associations</h3>
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<pre><code>class Deal < Sequel::Model
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# Us (left) <=> Them (right)
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many_to_many :images,
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left_id: :deal_id,
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right_id: :image_id,
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join_table: :image_links
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one_to_many :files,
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key: :deal_id,
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class: :DataFile,
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many_to_one :parent, class: self
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one_to_many :children, key: :parent_id, class: self
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one_to_many :gold_albums, class: :Album do |ds|
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ds.filter { copies_sold > 50000 }
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end
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</code></pre>
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<p>Provided by many_to_many</p>
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<pre><code>Deal[1].images
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Deal[1].add_image
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Deal[1].remove_image
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Deal[1].remove_all_images
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</code></pre>
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<h3 id="validations">Validations</h3>
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<pre><code> def validate
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super
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errors.add(:name, 'cannot be empty') if !name || name.empty?
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validates_presence [:title, :site]
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validates_unique :name
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validates_format /\Ahttps?:\/\//, :website, :message=>'is not a valid URL'
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validates_includes %w(a b c), :type
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validates_integer :rating
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validates_numeric :number
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validates_type String, [:title, :description]
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validates_integer :rating if new?
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# options: :message =>, :allow_nil =>, :allow_blank =>,
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# :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
|
|
</code></pre>
|
|
|
|
<h3 id="model-stuff">Model stuff</h3>
|
|
|
|
<pre><code>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!
|
|
</code></pre>
|
|
|
|
<h3 id="callbacks">Callbacks</h3>
|
|
|
|
<pre><code>before_create
|
|
after_create
|
|
|
|
before_validation
|
|
after_validation
|
|
before_save
|
|
before_update
|
|
UPDATE QUERY
|
|
after_update
|
|
after_save
|
|
|
|
before_destroy
|
|
DELETE QUERY
|
|
after_destroy
|
|
</code></pre>
|
|
|
|
<h3 id="schema">Schema</h3>
|
|
|
|
<pre><code>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
|
|
</code></pre>
|
|
|
|
<h3 id="unrestrict-primary-key">Unrestrict primary key</h3>
|
|
|
|
<pre><code>Category.create id: 'travel' # error
|
|
Category.unrestrict_primary_key
|
|
Category.create id: 'travel' # ok
|
|
</code></pre>
|
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