# CodeIgniter User Guide Version 2.1.0

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# Database Forge Class

The Database Forge Class contains functions that help you manage your database.

### Table of Contents

- Initializing the Forge Class
- Creating a Database
- Dropping a Database
- Adding Fields
- Adding Keys
- Creating a Table
- Dropping a Table
- Renaming a Table
- Modifying a Table

## Initializing the Forge Class

Important: In order to initialize the Forge class, your database driver must already be running, since the forge class relies on it.

Load the Forge Class as follows:

`$this->load->dbforge()`

Once initialized you will access the functions using the $this->dbforge object:

`$this->dbforge->some_function()`

## $this->dbforge->create_database('db_name')

Permits you to create the database specified in the first parameter. Returns TRUE/FALSE based on success or failure:

`if ($this->dbforge->create_database('my_db'))
{
echo 'Database created!';
}`

## $this->dbforge->drop_database('db_name')

Permits you to drop the database specified in the first parameter. Returns TRUE/FALSE based on success or failure:

`if ($this->dbforge->drop_database('my_db'))
{
echo 'Database deleted!';
}`

# Creating and Dropping Tables

There are several things you may wish to do when creating tables. Add fields, add keys to the table, alter columns. CodeIgniter provides a mechanism for this.

## Adding fields

Fields are created via an associative array. Within the array you must include a 'type' key that relates to the datatype of the field. For example, INT, VARCHAR, TEXT, etc. Many datatypes (for example VARCHAR) also require a 'constraint' key.

`$fields = array(
'users' => array(
'type' => 'VARCHAR',
'constraint' => '100',
),
);
// will translate to "users VARCHAR(100)" when the field is added.`

Additionally, the following key/values can be used:

- unsigned/true : to generate "UNSIGNED" in the field definition.
- default/value : to generate a default value in the field definition.
- null/true : to generate "NULL" in the field definition. Without this, the field will default to "NOT NULL".
- auto_increment/true : generates an auto_increment flag on the field. Note that the field type must be a type that supports this, such as integer.

`$fields = array(
'blog_id' => array(
'type' => 'INT',
'constraint' => 5,
'unsigned' => TRUE,
'auto_increment' => TRUE
),
'blog_title' => array(
'type' => 'VARCHAR',
'constraint' => '100',
),
'blog_author' => array(
'type' =>'VARCHAR',
'constraint' => '100',
'default' => 'King of Town',
),
'blog_description' => array(
'type' => 'TEXT',
'null' => TRUE,
),
);
`

After the fields have been defined, they can be added using $this->dbforge->add_field($fields); followed by a call to the create_table() function.

### $this->dbforge->add_field()

The add fields function will accept the above array.

### Passing strings as fields

If you know exactly how you want a field to be created, you can pass the string into the field definitions with add_field()

`$this->dbforge->add_field("label varchar(100) NOT NULL DEFAULT 'default label'");`

Note: Multiple calls to add_field() are cumulative.

### Creating an id field

There is a special exception for creating id fields. A field with type id will automatically be assinged as an INT(9) auto_incrementing Primary Key.

`$this->dbforge->add_field('id');
// gives id INT(9) NOT NULL AUTO_INCREMENT`

## Adding Keys

Generally speaking, you'll want your table to have Keys. This is accomplished with $this->dbforge->add_key('field'). An optional second parameter set to TRUE will make it a primary key. Note that add_key() must be followed by a call to create_table().

Multiple column non-primary keys must be sent as an array. Sample output below is for MySQL.

`$this->dbforge->add_key('blog_id', TRUE);
// gives PRIMARY KEY `blog_id` (`blog_id`)
$this->dbforge->add_key('blog_id', TRUE);
$this->dbforge->add_key('site_id', TRUE);
// gives PRIMARY KEY `blog_id_site_id` (`blog_id`, `site_id`)
$this->dbforge->add_key('blog_name');
// gives KEY `blog_name` (`blog_name`)
$this->dbforge->add_key(array('blog_name', 'blog_label'));
// gives KEY `blog_name_blog_label` (`blog_name`, `blog_label`)`

## Creating a table

After fields and keys have been declared, you can create a new table with

`$this->dbforge->create_table('table_name');
// gives CREATE TABLE table_name`

An optional second parameter set to TRUE adds an "IF NOT EXISTS" clause into the definition

`$this->dbforge->create_table('table_name', TRUE);
// gives CREATE TABLE IF NOT EXISTS table_name`

## Dropping a table

Executes a DROP TABLE sql

`$this->dbforge->drop_table('table_name');
// gives DROP TABLE IF EXISTS table_name`

## Renaming a table

Executes a TABLE rename

`$this->dbforge->rename_table('old_table_name', 'new_table_name');
// gives ALTER TABLE old_table_name RENAME TO new_table_name`

# Modifying Tables

## $this->dbforge->add_column()

The add_column() function is used to modify an existing table. It accepts the same field array as above, and can be used for an unlimited number of additional fields.

`$fields = array(
'preferences' => array('type' => 'TEXT')
);
$this->dbforge->add_column('table_name', $fields);
// gives ALTER TABLE table_name ADD preferences TEXT`

## $this->dbforge->drop_column()

Used to remove a column from a table.

`$this->dbforge->drop_column('table_name', 'column_to_drop');`

## $this->dbforge->modify_column()

The usage of this function is identical to add_column(), except it alters an existing column rather than adding a new one. In order to change the name you can add a "name" key into the field defining array.

`$fields = array(
'old_name' => array(
'name' => 'new_name',
'type' => 'TEXT',
),
);
$this->dbforge->modify_column('table_name', $fields);
// gives ALTER TABLE table_name CHANGE old_name new_name TEXT`