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<com:TContent ID="Main">
<h1>Creating Database</h1>
<p>
Most Web applications use database to keep data. Our blog system is not an exception. In this section, we will describe how to write database-driven pages for our blog system. We will use techniques including <a href="http://www.pradosoft.com/demos/quickstart/?page=Database.DAO">database access object (DAO)</a> and <a href="http://www.pradosoft.com/demos/quickstart/?page=Database.ActiveRecord">Active Record</a>.
</p>
<p>
For tutorial purpose, we have simplified the requirements of our blog system so that it only needs to deal with user and post data. We thus create two database tables, <tt>users</tt> and <tt>posts</tt>, as shown in the following entity-relationship (ER) diagram.
</p>
<img src="<%~ ER.gif %>" />
<p>
We use a SQLite 3 database to keep our data. We first convert the ER diagram into the following SQL statements and save them in the file <tt>protected/schema.sql</tt>.
</p>
<com:TTextHighlighter CssClass="source">
/* create users table */
CREATE TABLE users (
username VARCHAR(128) NOT NULL PRIMARY KEY,
email VARCHAR(128) NOT NULL UNIQUE,
password VARCHAR(128) NOT NULL, /* plain text password */
role INTEGER NOT NULL, /* 0: normal user, 1: administrator */
first_name VARCHAR(128),
last_name VARCHAR(128)
);
/* create posts table */
CREATE TABLE posts (
post_id INTEGER NOT NULL PRIMARY KEY,
author VARCHAR(128) NOT NULL, /* references users.username */
create_time INTEGER NOT NULL, /* UNIX timestamp */
title VARCHAR(256) NOT NULL, /* title of the post */
content TEXT NOT NULL /* content of the post */
);
/* insert some initial data records for testing */
INSERT INTO users VALUES ('admin', 'admin@example.com', 'demo', 1, 'Qiang', 'Xue');
INSERT INTO users VALUES ('demo', 'demo@example.com', 'demo', 0, 'Wei', 'Zhuo');
INSERT INTO posts VALUES (NULL, 'admin', 1175708482, 'first post', 'this is my first post');
</com:TTextHighlighter>
<com:NoteBox>
SQLite does not support <a href="http://www.sqlite.org/omitted.html">foreign key constraint</a>. Therefore, we will write PHP code to ensure that the <tt>posts.author</tt> field contains valid data. Also, we are exploiting the fact that the <tt>posts.post_id</tt> field is <a href="http://www.sqlite.org/autoinc.html">auto-incremental</a> if we assign NULL to it.
</com:NoteBox>
<p>
We use the <a href="http://www.sqlite.org/download.html">SQLite command line tool</a> to create the SQLite database. We first create a directory <tt>protected/data</tt> to hold the SQLite database file. Per SQLite's requirement, this directory and the database file to be created must be set writable by the Web server process. We now execute the following command under the directory <tt>protected/data</tt>:
</p>
<com:TTextHighlighter CssClass="source">
sqlite3 blog.db < ../schema.sql
</com:TTextHighlighter>
<p>
The database has been created as <tt>protected/data/blog.db</tt> and we shall see the following directories and files:
</p>
<img src="<%~ directories.gif %>" />
</com:TContent>
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