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docs/guide/start-databases.md
Working with Databases
======================
In this section, we will describe how to create a new page to display the country data fetched from
from a database table `country`. To achieve this goal, you will configure a database connection,
create an [Active Record](db-active-record.md) class, and then create an [action](structure-controllers.md)
and a [view](structure-views.md).
This section will describe how to create a new page that displays country data fetched from
from a database table named `country`. To achieve this goal, you will configure a database connection,
create an [Active Record](db-active-record.md) class, and define an [action](structure-controllers.md),
and create a [view](structure-views.md).
Through this tutorial, you will learn
Through this tutorial, you will learn how to:
* How to configure a DB connection;
* How to define an Active Record class;
* How to query data using the Active Record class;
* How to display data in a view in a paginated fashion.
* Configure a DB connection
* Define an Active Record class
* Query data using the Active Record class
* Display data in a view in a paginated fashion
Note that in order to finish this section, you should have basic knowledge and experience about databases.
In particular, you should know how to create a database and how to execute SQL statements using a DB client tool.
Note that in order to finish this section, you should have basic knowledge and experience using databases.
In particular, you should know how to create a database, and how to execute SQL statements using a DB client tool.
Preparing a Database <a name="preparing-database"></a>
Preparing the Database <a name="preparing-database"></a>
--------------------
To begin with, create a database named `yii2basic` from which you will fetch data in your application.
You may create a SQLite, MySQL, PostgreSQL, MSSQL or Oracle database. For simplicity, we will use MySQL
in the following description.
To begin, create a database named `yii2basic`, from which you will fetch data in your application.
You may create an SQLite, MySQL, PostgreSQL, MSSQL or Oracle database, as Yii has built-in support for many database applications. For simplicity, MySQL will be assumed in the following description.
Create a table named `country` in the database and insert some sample data. You may run the following SQL statements.
Next, create a table named `country` in the database, and insert some sample data. You may run the following SQL statements to do so:
```sql
CREATE TABLE `country` (
`code` char(2) NOT NULL PRIMARY KEY,
`name` char(52) NOT NULL,
`population` int(11) NOT NULL DEFAULT '0'
`code` CHAR(2) NOT NULL PRIMARY KEY,
`name` CHAR(52) NOT NULL,
`population` INT(11) NOT NULL DEFAULT '0'
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `Country` VALUES ('AU','Australia',18886000);
......@@ -45,19 +44,17 @@ INSERT INTO `Country` VALUES ('RU','Russia',146934000);
INSERT INTO `Country` VALUES ('US','United States',278357000);
```
To this end, you have a database named `yii2basic`, and within this database there is a `country` table
with ten rows of data.
At this point, you have a database named `yii2basic`, and within it a `country` table with three columns, containing ten rows of data.
Configuring a DB Connection <a name="configuring-db-connection"></a>
Configuring the DB Connection <a name="configuring-db-connection"></a>
---------------------------
Make sure you have installed the [PDO](http://www.php.net/manual/en/book.pdo.php) PHP extension and
Before proceeding, make sure you have installed both the [PDO](http://www.php.net/manual/en/book.pdo.php) PHP extension and
the PDO driver for the database you are using (e.g. `pdo_mysql` for MySQL). This is a basic requirement
if your application uses a relational database.
Open the file `config/db.php` and adjust the content based on your database information. By default,
the file contains the following content:
With those installed, open the file `config/db.php` and change the parameters to be correct for your database. By default,
the file contains the following:
```php
<?php
......@@ -71,13 +68,13 @@ return [
];
```
This is a typical file-based [configuration](concept-configurations.md). It specifies the parameters
The `config/db.php` file is a typical file-based [configuration](concept-configurations.md) tool. This particular configuration file specifies the parameters
needed to create and initialize a [[yii\db\Connection]] instance through which you can make SQL queries
against the underlying database.
The DB connection configured above can be accessed in the code via the expression `Yii::$app->db`.
The DB connection configured above can be accessed in the application code via the expression `Yii::$app->db`.
> Info: The `config/db.php` file will be included in the main application configuration `config/web.php`
> Info: The `config/db.php` file will be included by the main application configuration `config/web.php`,
which specifies how the [application](structure-applications.md) instance should be initialized.
For more information, please refer to the [Configurations](concept-configurations.md) section.
......@@ -85,8 +82,8 @@ The DB connection configured above can be accessed in the code via the expressio
Creating an Active Record <a name="creating-active-record"></a>
-------------------------
To represent and fetch the data in the `country` table, create an [Active Record](db-active-record.md)
class named `Country` and save it in the file `models/Country.php`.
To represent and fetch the data in the `country` table, create an [Active Record](db-active-record.md)-derived
class named `Country`, and save it in the file `models/Country.php`.
```php
<?php
......@@ -100,12 +97,13 @@ class Country extends ActiveRecord
}
```
The `Country` class extends from [[yii\db\ActiveRecord]]. You do not need to write any code inside of it.
Yii will guess the associated table name from the class name. In case this does not work, you may
The `Country` class extends from [[yii\db\ActiveRecord]]. You do not need to write any code inside of it! With just the above code,
Yii will guess the associated table name from the class name.
> Inof: If no direct match can be made from the class name to the table name, you can
override the [[yii\db\ActiveRecord::tableName()]] method to explicitly specify the associated table name.
Using the `Country` class, you can manipulate the data in the `country` table easily. Below are some
code snippets showing how you can make use of the `Country` class.
Using the `Country` class, you can easily manipulate data in the `country` table, as shown in these snippets:
```php
use app\models\Country;
......@@ -124,9 +122,8 @@ $country->name = 'U.S.A.';
$country->save();
```
> Info: Active Record is a powerful way of accessing and manipulating database data in an object-oriented fashion.
You may find more detailed information in the [Active Record](db-active-record.md). Besides Active Record, you may also
use a lower-level data accessing method called [Data Access Objects](db-dao.md).
> Info: Active Record is a powerful way to access and manipulate database data in an object-oriented fashion.
You may find more detailed information in the [Active Record](db-active-record.md) section. Alternatively, you may also interact with a database using a lower-level data accessing method called [Data Access Objects](db-dao.md).
Creating an Action <a name="creating-action"></a>
......
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