Ruby對象映射框架：Sequel

Sequel 是一個 Ruby 語言的對象映射框架（ORM），提供了線程安全、連接池以及 DSL 語言用來構造查詢和表模型。

特性:

• Sequel provides thread safety, connection pooling and a concise DSL for constructing SQL queries and table schemas.
• Sequel includes a comprehensive ORM layer for mapping records to Ruby objects and handling associated records.
• Sequel supports advanced database features such as prepared statements, bound variables, stored procedures, savepoints, two-phase commit, transaction isolation, master/slave configurations, and database sharding.
• Sequel currently has adapters for ADO, Amalgalite, DataObjects, DB2, DBI, Firebird, IBM_DB, Informix, JDBC, MySQL, Mysql2, ODBC, OpenBase, Oracle, PostgreSQL, SQLite3, Swift, and TinyTDS.

require "rubygems"
require "sequel"

# connect to an in-memory database
DB = Sequel.sqlite

# create an items table
DB.create_table :items do
  primary_key :id
  String :name
  Float :price
end

# create a dataset from the items table
items = DB[:items]

# populate the table
items.insert(:name => 'abc', :price => rand * 100)
items.insert(:name => 'def', :price => rand * 100)
items.insert(:name => 'ghi', :price => rand * 100)

# print out the number of records
puts "Item count: #{items.count}"

# print out the average price
puts "The average price is: #{items.avg(:price)}"

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