c# .net barcode generator free ActiveRecord: A Sneak Peek in Font

Maker Data Matrix in Font ActiveRecord: A Sneak Peek

So far in this chapter you ve worked directly with databases using a whole new language: SQL. Working with a database in this way is more efficient and reliable than putting data into text files, as you did earlier, but ActiveRecord makes it easier still. ActiveRecord is a product of the Ruby on Rails framework, which we ll be covering in 13, but can be used entirely independently of it. ActiveRecord will be covered in more depth in that chapter, but deserves a brief summary here. ActiveRecord abstracts away all the details of SQL and database design and makes it possible to relate to items within databases in an object-oriented fashion, as you did with PStore. ActiveRecord gives you objects that correspond to rows and classes that correspond to tables, and you can work with the data using Ruby syntax, like so:

This code looks through the people table for a row whose name column matches Chris, and puts an object relating to that row into person. ActiveRecord makes attributes available for all that row s columns, so changing the age column is as easy as assigning to the object s attribute. However, once the object s value has been changed, you issue the save method to save the changes back to the database.

Note The pluralization from a Person class to a people table is an automatic part of ActiveRecord s

The previous code could replace SQL such as this:

SELECT * FROM people WHERE name = "Chris" UPDATE people SET age = 50 WHERE name = "Chris"

Even SQL gurus familiar with Ruby tend to find Ruby s syntax more natural, particularly in the scope of a Ruby program. There s no need to mix two different languages in one program if both sets of features can be provided in Ruby alone. ActiveRecord will be covered in detail in 13.

Note ActiveRecord is not the only library to offer features that relate objects to database tables. Og and

Lafcadio (http://lafcadio.rubyforge.org/) are two alternatives, though they re far less popular than ActiveRecord.

Summary

In this chapter we ve looked at how data can flow into and out of your Ruby programs. Initially we looked at the low-level concept of I/O streams before quickly moving on to the pragmatism of databases. Databases provide a way to work with data in a more abstracted fashion without worrying about the underlying structure of the data on the computer s filesystem. Indeed, databases can be located within memory or on totally different machines, and our code could remain the same. Let s reflect on the main concepts covered in this chapter: I/O: Input/Output. The concept of receiving input and sending output by various means on a computer, often via I/O streams. I/O stream: A channel along which data can be sent and/or received. Standard input (stdin): A stream that relates to the default way of accepting data into the application, usually the keyboard. Standard output (stdout): A stream that relates to the default way of outputting data from the application, usually to the screen. File pointer: An abstract reference to the current location within a file. Database: An organized collection of data structured in a way that makes it easy to be accessed programmatically.

CSV: Comma-Separated Values. A way of structuring data with attributes separated with commas. CSV can be stored in plain text files. Marshalling: The process of converting a live data structure or object into a flat set of data that can be stored on disk, sent across a network, and then can be used to reconstruct the original data structure or object elsewhere or at some other time. Table: A collection of data organized into rows, with multiple columns, where each column represents a different attribute of each row. There are usually multiple tables within a database, containing different types of data. SQLite: An open source, public-domain relational database API and library that works on a single-user basis on a local machine. It supports SQL as its querying language. MySQL: An open source relational database system available in both community and professional editions. It is maintained by MySQL AB. Web hosting companies commonly offer MySQL database support. PostgreSQL: A free, open source relational database system licensed under the BSD license, making it possible to repackage and sell within commercial products. PostgreSQL is often considered to be of higher performance and have better conformity to SQL standards than MySQL, although it s less commonly used. Oracle: A commercial relational database system developed by Oracle Corp. It s generally used by large businesses for managing extremely large datasets. Primary key: A column (or multiple columns) on a table whose data uniquely identifies each row. DBI: DataBase Interface. A database-agnostic library that makes it easy to communicate between Ruby and database systems. SQL: Structured Query Language. A language specifically designed to create, amend, retrieve, and otherwise manipulate data in relational database systems. ActiveRecord: A library that abstracts databases, rows, columns, and SQL into standard Ruby syntax using classes and objects. It s a major part of the Ruby on Rails framework, which is covered in detail in 13.