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数据库访问 (DAO)

数据库访问 (DAO)

Yii 包含了一个建立在 PHP PDO 之上的数据访问层 (DAO). DAO为不同的数据库提供了一套统一的API. 其中`ActiveRecord` 提供了数据库与模型(MVC 中的 M,Model) 的交互,`QueryBuilder` 用于创建动态的查询语句. DAO提供了简单高效的SQL查询,可以用在与数据库交互的各个地方.

Yii 默认支持以下数据库 (DBMS):

  • MySQL
  • MariaDB
  • SQLite
  • PostgreSQL
  • CUBRID: 版本 >= 9.3 . (由于PHP PDO 扩展的一个bug 引用值会无效,所以你需要在 CUBRID的客户端和服务端都使用 9.3 )
  • Oracle
  • MSSQL: 版本>=2005.

配置

开始使用数据库首先需要配置数据库连接组件,通过添加 db 组件到应用配置实现("基础的" Web 应用是 config/web.php),DSN( Data Source Name )是数据源名称,用于指定数据库信息.如下所示:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">return</span> [

    <span style="box-sizing: border-box;">// ...</span>

    <span style="box-sizing: border-box;">'components'</span> => [

        <span style="box-sizing: border-box;">// ...</span>

        <span style="box-sizing: border-box;">'db'</span> => [

            <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

            <span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'mysql:host=localhost;dbname=mydatabase'</span>, <span style="box-sizing: border-box;">// MySQL, MariaDB</span>

            <span style="box-sizing: border-box;">//'dsn' => 'sqlite:/path/to/database/file', // SQLite</span>

            <span style="box-sizing: border-box;">//'dsn' => 'pgsql:host=localhost;port=5432;dbname=mydatabase', // PostgreSQL</span>

            <span style="box-sizing: border-box;">//'dsn' => 'cubrid:dbname=demodb;host=localhost;port=33000', // CUBRID</span>

            <span style="box-sizing: border-box;">//'dsn' => 'sqlsrv:Server=localhost;Database=mydatabase', // MS SQL Server, sqlsrv driver</span>

            <span style="box-sizing: border-box;">//'dsn' => 'dblib:host=localhost;dbname=mydatabase', // MS SQL Server, dblib driver</span>

            <span style="box-sizing: border-box;">//'dsn' => 'mssql:host=localhost;dbname=mydatabase', // MS SQL Server, mssql driver</span>

            <span style="box-sizing: border-box;">//'dsn' => 'oci:dbname=//localhost:1521/mydatabase', // Oracle</span>

            <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'root'</span>, <span style="box-sizing: border-box;">//数据库用户名</span>

            <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>, <span style="box-sizing: border-box;">//数据库密码</span>

            <span style="box-sizing: border-box;">'charset'</span> => <span style="box-sizing: border-box;">'utf8'</span>,

        ],

    ],

    <span style="box-sizing: border-box;">// ...</span>

];

</code>

请参考PHP manual获取更多有关 DSN 格式信息。 配置连接组件后可以使用以下语法访问:

$connection = \Yii::$app->db;

请参考yii\db\Connection获取可配置的属性列表。 如果你想通过ODBC连接数据库,则需要配置yii\db\Connection::driverName 属性,例如:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">'db'</span> => [

    <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

    <span style="box-sizing: border-box;">'driverName'</span> => <span style="box-sizing: border-box;">'mysql'</span>,

    <span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'odbc:Driver={MySQL};Server=localhost;Database=test'</span>,

    <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'root'</span>,

    <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>,

],

</code>

注意:如果需要同时使用多个数据库可以定义 多个 连接组件:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">return</span> [

    <span style="box-sizing: border-box;">// ...</span>

    <span style="box-sizing: border-box;">'components'</span> => [

        <span style="box-sizing: border-box;">// ...</span>

        <span style="box-sizing: border-box;">'db'</span> => [

            <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

            <span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'mysql:host=localhost;dbname=mydatabase'</span>,

            <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'root'</span>,

            <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>,

            <span style="box-sizing: border-box;">'charset'</span> => <span style="box-sizing: border-box;">'utf8'</span>,

        ],

        <span style="box-sizing: border-box;">'secondDb'</span> => [

            <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

            <span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'sqlite:/path/to/database/file'</span>,

        ],

    ],

    <span style="box-sizing: border-box;">// ...</span>

];

</code>

在代码中通过以下方式使用:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$primaryConnection</span> = \Yii::<span style="box-sizing: border-box;">$app-</span>>db;

<span style="box-sizing: border-box;">$secondaryConnection</span> = \Yii::<span style="box-sizing: border-box;">$app-</span>>secondDb;

</code>

如果不想定义数据库连接为全局应用组件,可以在代码中直接初始化使用:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$connection</span> = new \yii\db\Connection([

    <span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">$dsn</span>,

     <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">$username</span>,

     <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">$password</span>,

]);

<span style="box-sizing: border-box;">$connection-</span>>open();

</code>

>小提示:如果在创建了连接后需要执行额外的 SQL 查询,可以添加以下代码到应用配置文件:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">return</span> [

    <span style="box-sizing: border-box;">// ...</span>

    <span style="box-sizing: border-box;">'components'</span> => [

        <span style="box-sizing: border-box;">// ...</span>

        <span style="box-sizing: border-box;">'db'</span> => [

            <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

            <span style="box-sizing: border-box;">// ...</span>

            <span style="box-sizing: border-box;">'on afterOpen'</span> => <span style="box-sizing: border-box;"><span style="box-sizing: border-box;">function</span><span style="box-sizing: border-box;">(<span style="box-sizing: border-box;">$event</span>)</span> </span>{

                <span style="box-sizing: border-box;">$event</span>->sender->createCommand(<span style="box-sizing: border-box;">"SET time_zone = 'UTC'"</span>)->execute();

            }

        ],

    ],

    <span style="box-sizing: border-box;">// ...</span>

];

</code>

SQL 基础查询

一旦有了连接实例就可以通过yii\db\Command执行 SQL 查询。

SELECT 查询

查询返回多行:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection-</span>>createCommand(<span style="box-sizing: border-box;">'SELECT * FROM post'</span>);

<span style="box-sizing: border-box;">$posts</span> = <span style="box-sizing: border-box;">$command-</span>>queryAll();

</code>

返回单行:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection-</span>>createCommand(<span style="box-sizing: border-box;">'SELECT * FROM post WHERE id=1'</span>);

<span style="box-sizing: border-box;">$post</span> = <span style="box-sizing: border-box;">$command-</span>>queryOne();

</code>

查询多行单值:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection-</span>>createCommand(<span style="box-sizing: border-box;">'SELECT title FROM post'</span>);

<span style="box-sizing: border-box;">$titles</span> = <span style="box-sizing: border-box;">$command-</span>>queryColumn();

</code>

查询标量值/计算值:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection-</span>>createCommand(<span style="box-sizing: border-box;">'SELECT COUNT(*) FROM post'</span>);

<span style="box-sizing: border-box;">$postCount</span> = <span style="box-sizing: border-box;">$command-</span>>queryScalar();

</code>

UPDATE, INSERT, DELETE 更新、插入和删除等

如果执行 SQL 不返回任何数据可使用命令中的 execute 方法:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection-</span>>createCommand(<span style="box-sizing: border-box;">'UPDATE post SET status=1 WHERE id=1'</span>);

<span style="box-sizing: border-box;">$command-</span>>execute();

</code>

你可以使用insert,update,delete 方法,这些方法会根据参数生成合适的SQL并执行.

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">// INSERT</span><span style="box-sizing: border-box;">$connection</span>->createCommand()->insert(<span style="box-sizing: border-box;">'user'</span>, [

    <span style="box-sizing: border-box;">'name'</span> => <span style="box-sizing: border-box;">'Sam'</span>,

    <span style="box-sizing: border-box;">'age'</span> => <span style="box-sizing: border-box;">30</span>,

])->execute();

 

<span style="box-sizing: border-box;">// INSERT 一次插入多行</span><span style="box-sizing: border-box;">$connection</span>->createCommand()->batchInsert(<span style="box-sizing: border-box;">'user'</span>, [<span style="box-sizing: border-box;">'name'</span>, <span style="box-sizing: border-box;">'age'</span>], [

    [<span style="box-sizing: border-box;">'Tom'</span>, <span style="box-sizing: border-box;">30</span>],

    [<span style="box-sizing: border-box;">'Jane'</span>, <span style="box-sizing: border-box;">20</span>],

    [<span style="box-sizing: border-box;">'Linda'</span>, <span style="box-sizing: border-box;">25</span>],

])->execute();

 

<span style="box-sizing: border-box;">// UPDATE</span><span style="box-sizing: border-box;">$connection</span>->createCommand()->update(<span style="box-sizing: border-box;">'user'</span>, [<span style="box-sizing: border-box;">'status'</span> => <span style="box-sizing: border-box;">1</span>], <span style="box-sizing: border-box;">'age > 30'</span>)->execute();

 

<span style="box-sizing: border-box;">// DELETE</span><span style="box-sizing: border-box;">$connection</span>->createCommand()->delete(<span style="box-sizing: border-box;">'user'</span>, <span style="box-sizing: border-box;">'status = 0'</span>)->execute();

</code>

引用的表名和列名

大多数时间都使用以下语法来安全地引用表名和列名:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$sql</span> = <span style="box-sizing: border-box;">"SELECT COUNT($column) FROM {{table}}"</span>;

<span style="box-sizing: border-box;">$rowCount</span> = <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql</span>)->queryScalar();

</code>

以上代码$column 会转变为引用恰当的列名,而{{table}} 就转变为引用恰当的表名。 表名有个特殊的变量 {{%Y}} ,如果设置了表前缀使用该变体可以自动在表名前添加前缀:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$sql</span> = <span style="box-sizing: border-box;">"SELECT COUNT($column) FROM {{%$table}}"</span>;

<span style="box-sizing: border-box;">$rowCount</span> = <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql</span>)->queryScalar();

</code>

如果在配置文件如下设置了表前缀,以上代码将在 tbl_table 这个表查询结果:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">return</span> [

    <span style="box-sizing: border-box;">// ...</span>

    <span style="box-sizing: border-box;">'components'</span> => [

        <span style="box-sizing: border-box;">// ...</span>

        <span style="box-sizing: border-box;">'db'</span> => [

            <span style="box-sizing: border-box;">// ...</span>

            <span style="box-sizing: border-box;">'tablePrefix'</span> => <span style="box-sizing: border-box;">'tbl_'</span>,

        ],

    ],

];

</code>

手工引用表名和列名的另一个选择是使用yii\db\Connection::quoteTableName() 和 yii\db\Connection::quoteColumnName():

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$column</span> = <span style="box-sizing: border-box;">$connection</span>->quoteColumnName(<span style="box-sizing: border-box;">$column</span>);

<span style="box-sizing: border-box;">$table</span> = <span style="box-sizing: border-box;">$connection</span>->quoteTableName(<span style="box-sizing: border-box;">$table</span>);

<span style="box-sizing: border-box;">$sql</span> = <span style="box-sizing: border-box;">"SELECT COUNT($column) FROM $table"</span>;

<span style="box-sizing: border-box;">$rowCount</span> = <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql</span>)->queryScalar();

</code>

预处理语句

为安全传递查询参数可以使用预处理语句,首先应当使用:placeholder占位,再将变量绑定到对应占位符:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">'SELECT * FROM post WHERE id=:id'</span>);

<span style="box-sizing: border-box;">$command</span>->bindValue(<span style="box-sizing: border-box;">':id'</span>, <span style="box-sizing: border-box;">$_GET</span>[<span style="box-sizing: border-box;">'id'</span>]);

<span style="box-sizing: border-box;">$post</span> = <span style="box-sizing: border-box;">$command</span>->query();

</code>

另一种用法是准备一次预处理语句而执行多次查询:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$command</span> = <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">'DELETE FROM post WHERE id=:id'</span>);

<span style="box-sizing: border-box;">$command</span>->bindParam(<span style="box-sizing: border-box;">':id'</span>, <span style="box-sizing: border-box;">$id</span>);

 

<span style="box-sizing: border-box;">$id</span> = <span style="box-sizing: border-box;">1</span>;

<span style="box-sizing: border-box;">$command</span>->execute();

 

<span style="box-sizing: border-box;">$id</span> = <span style="box-sizing: border-box;">2</span>;

<span style="box-sizing: border-box;">$command</span>->execute();

</code>

>提示,在执行前绑定变量,然后在每个执行中改变变量的值(一般用在循环中)比较高效.

事务

当你需要顺序执行多个相关的的query时,你可以把他们封装到一个事务中去保护数据一致性.Yii提供了一个简单的接口来实现事务操作. 如下执行 SQL 事务查询语句:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$transaction</span> = <span style="box-sizing: border-box;">$connection</span>->beginTransaction();

<span style="box-sizing: border-box;">try</span> {

    <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql1</span>)->execute();

     <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql2</span>)->execute();

    <span style="box-sizing: border-box;">// ... 执行其他 SQL 语句 ...</span>

    <span style="box-sizing: border-box;">$transaction</span>->commit();

} <span style="box-sizing: border-box;">catch</span>(<span style="box-sizing: border-box;">Exception</span> <span style="box-sizing: border-box;">$e</span>) {

    <span style="box-sizing: border-box;">$transaction</span>->rollBack();

}

</code>

我们通过yii\db\Connection::beginTransaction()开始一个事务,通过try catch 捕获异常.当执行成功,通过yii\db\Transaction::commit()提交事务并结束,当发生异常失败通过yii\db\Transaction::rollBack()进行事务回滚.

如需要也可以嵌套多个事务:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">// 外部事务</span><span style="box-sizing: border-box;">$transaction1</span> = <span style="box-sizing: border-box;">$connection</span>->beginTransaction();

<span style="box-sizing: border-box;">try</span> {

    <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql1</span>)->execute();

 

    <span style="box-sizing: border-box;">// 内部事务</span>

    <span style="box-sizing: border-box;">$transaction2</span> = <span style="box-sizing: border-box;">$connection</span>->beginTransaction();

    <span style="box-sizing: border-box;">try</span> {

        <span style="box-sizing: border-box;">$connection</span>->createCommand(<span style="box-sizing: border-box;">$sql2</span>)->execute();

        <span style="box-sizing: border-box;">$transaction2</span>->commit();

    } <span style="box-sizing: border-box;">catch</span> (<span style="box-sizing: border-box;">Exception</span> <span style="box-sizing: border-box;">$e</span>) {

        <span style="box-sizing: border-box;">$transaction2</span>->rollBack();

    }

 

    <span style="box-sizing: border-box;">$transaction1</span>->commit();

} <span style="box-sizing: border-box;">catch</span> (<span style="box-sizing: border-box;">Exception</span> <span style="box-sizing: border-box;">$e</span>) {

    <span style="box-sizing: border-box;">$transaction1</span>->rollBack();

}

</code>

>注意你使用的数据库必须支持Savepoints才能正确地执行,以上代码在所有关系数据中都可以执行,但是只有支持Savepoints才能保证安全性。

Yii 也支持为事务设置隔离级别isolation levels,当执行事务时会使用数据库默认的隔离级别,你也可以为事物指定隔离级别. Yii 提供了以下常量作为常用的隔离级别

  • \yii\db\Transaction::READ_UNCOMMITTED - 允许读取改变了的还未提交的数据,可能导致脏读、不可重复读和幻读
  • \yii\db\Transaction::READ_COMMITTED - 允许并发事务提交之后读取,可以避免脏读,可能导致重复读和幻读。
  • \yii\db\Transaction::REPEATABLE_READ - 对相同字段的多次读取结果一致,可导致幻读。
  • \yii\db\Transaction::SERIALIZABLE - 完全服从ACID的原则,确保不发生脏读、不可重复读和幻读。

你可以使用以上常量或者使用一个string字符串命令,在对应数据库中执行该命令用以设置隔离级别,比如对于postgres有效的命令为SERIALIZABLE READ ONLY DEFERRABLE.

>注意:某些数据库只能针对连接来设置事务隔离级别,所以你必须要为连接明确制定隔离级别.目前受影响的数据库:MSSQL SQLite

>注意:SQLite 只支持两种事务隔离级别,所以你只能设置READ UNCOMMITTED 和 SERIALIZABLE.使用其他隔离级别会抛出异常.

>注意:PostgreSQL 不允许在事务开始前设置隔离级别,所以你不能在事务开始时指定隔离级别.你可以在事务开始之后调用yii\db\Transaction::setIsolationLevel() 来设置.

关于隔离级别[isolation levels]: http://en.wikipedia.org/wiki/Isolation_(database_systems)#Isolation_levels

数据库复制和读写分离

很多数据库支持数据库复制 database replication来提高可用性和响应速度. 在数据库复制中,数据总是从主服务器 到 从服务器. 所有的插入和更新等写操作在主服务器执行,而读操作在从服务器执行.

通过配置yii\db\Connection可以实现数据库复制和读写分离.

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;">[

    <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

 

    <span style="box-sizing: border-box;">// 配置主服务器</span>

    <span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for master server'</span>,

    <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'master'</span>,

    <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>,

 

    <span style="box-sizing: border-box;">// 配置从服务器</span>

    <span style="box-sizing: border-box;">'slaveConfig'</span> => [

        <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'slave'</span>,

        <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>,

        <span style="box-sizing: border-box;">'attributes'</span> => [

            <span style="box-sizing: border-box;">// use a smaller connection timeout</span>

            PDO::ATTR_TIMEOUT => <span style="box-sizing: border-box;">10</span>,

        ],

    ],

 

    <span style="box-sizing: border-box;">// 配置从服务器组</span>

    <span style="box-sizing: border-box;">'slaves'</span> => [

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 1'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 2'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 3'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 4'</span>],

    ],

]

</code>

以上的配置实现了一主多从的结构,从服务器用以执行读查询,主服务器执行写入查询,读写分离的功能由后台代码自动完成.调用者无须关心.例如:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">// 使用以上配置创建数据库连接对象</span><span style="box-sizing: border-box;">$db</span> = Yii::createObject(<span style="box-sizing: border-box;">$config</span>);

 

<span style="box-sizing: border-box;">// 通过从服务器执行查询操作</span><span style="box-sizing: border-box;">$rows</span> = <span style="box-sizing: border-box;">$db</span>->createCommand(<span style="box-sizing: border-box;">'SELECT * FROM user LIMIT 10'</span>)->queryAll();

 

<span style="box-sizing: border-box;">// 通过主服务器执行更新操作</span><span style="box-sizing: border-box;">$db</span>->createCommand(<span style="box-sizing: border-box;">"UPDATE user SET username='demo' WHERE id=1"</span>)->execute();

</code>

>注意:通过yii\db\Command::execute() 执行的查询被认为是写操作,所有使用yii\db\Command来执行的其他查询方法被认为是读操作.你可以通过$db->slave得到当前正在使用能够的从服务器.

Connection组件支持从服务器的负载均衡和故障转移,当第一次执行读查询时,会随即选择一个从服务器进行连接,如果连接失败则又选择另一个,如果所有从服务器都不可用,则会连接主服务器。你可以配置yii\db\Connection::serverStatusCache来记住那些不能连接的从服务器,使Yii 在一段时间[[yii\db\Connection::serverRetryInterval].内不会重复尝试连接那些根本不可用的从服务器.

>注意:在上述配置中,每个从服务器连接超时时间被指定为10s. 如果在10s内不能连接,则被认为该服务器已经挂掉.你也可以自定义超时参数.

你也可以配置多主多从的结构,例如:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;">[

    <span style="box-sizing: border-box;">'class'</span> => <span style="box-sizing: border-box;">'yii\db\Connection'</span>,

 

    <span style="box-sizing: border-box;">// 配置主服务器</span>

    <span style="box-sizing: border-box;">'masterConfig'</span> => [

        <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'master'</span>,

        <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>,

        <span style="box-sizing: border-box;">'attributes'</span> => [

            <span style="box-sizing: border-box;">// use a smaller connection timeout</span>

            PDO::ATTR_TIMEOUT => <span style="box-sizing: border-box;">10</span>,

        ],

    ],

 

    <span style="box-sizing: border-box;">// 配置主服务器组</span>

    <span style="box-sizing: border-box;">'masters'</span> => [

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for master server 1'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for master server 2'</span>],

    ],

 

    <span style="box-sizing: border-box;">// 配置从服务器</span>

    <span style="box-sizing: border-box;">'slaveConfig'</span> => [

        <span style="box-sizing: border-box;">'username'</span> => <span style="box-sizing: border-box;">'slave'</span>,

        <span style="box-sizing: border-box;">'password'</span> => <span style="box-sizing: border-box;">''</span>,

        <span style="box-sizing: border-box;">'attributes'</span> => [

            <span style="box-sizing: border-box;">// use a smaller connection timeout</span>

            PDO::ATTR_TIMEOUT => <span style="box-sizing: border-box;">10</span>,

        ],

    ],

 

    <span style="box-sizing: border-box;">// 配置从服务器组</span>

    <span style="box-sizing: border-box;">'slaves'</span> => [

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 1'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 2'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 3'</span>],

        [<span style="box-sizing: border-box;">'dsn'</span> => <span style="box-sizing: border-box;">'dsn for slave server 4'</span>],

    ],

]

</code>

上述配置制定了2个主服务器和4个从服务器.Connection组件也支持主服务器的负载均衡和故障转移,与从服务器不同的是,如果所有主服务器都不可用,则会抛出异常.

>注意:当你使用yii\db\Connection::masters来配置一个或多个主服务器时,Connection中关于数据库连接的其他属性(例如:dsn,usernamepassword)都会被忽略.

事务默认使用主服务器的连接,并且在事务执行中的所有操作都会使用主服务器的连接,例如:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">// 在主服务器连接上开始事务</span><span style="box-sizing: border-box;">$transaction</span> = <span style="box-sizing: border-box;">$db</span>->beginTransaction();

 

<span style="box-sizing: border-box;">try</span> {

    <span style="box-sizing: border-box;">// 所有的查询都在主服务器上执行</span>

    <span style="box-sizing: border-box;">$rows</span> = <span style="box-sizing: border-box;">$db</span>->createCommand(<span style="box-sizing: border-box;">'SELECT * FROM user LIMIT 10'</span>)->queryAll();

    <span style="box-sizing: border-box;">$db</span>->createCommand(<span style="box-sizing: border-box;">"UPDATE user SET username='demo' WHERE id=1"</span>)->execute();

 

    <span style="box-sizing: border-box;">$transaction</span>->commit();

} <span style="box-sizing: border-box;">catch</span>(\<span style="box-sizing: border-box;">Exception</span> <span style="box-sizing: border-box;">$e</span>) {

    <span style="box-sizing: border-box;">$transaction</span>->rollBack();

    <span style="box-sizing: border-box;">throw</span> <span style="box-sizing: border-box;">$e</span>;

}

</code>

如果你想在从服务器上执行事务操作则必须要明确地指定,比如:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$transaction</span> = <span style="box-sizing: border-box;">$db</span>->slave->beginTransaction();

</code>

有时你想强制使用主服务器来执行读查询,你可以调用seMaster()方法.

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$rows</span> = <span style="box-sizing: border-box;">$db</span>->useMaster(<span style="box-sizing: border-box;"><span style="box-sizing: border-box;">function</span> <span style="box-sizing: border-box;">(<span style="box-sizing: border-box;">$db</span>)</span> </span>{

    <span style="box-sizing: border-box;">return</span> <span style="box-sizing: border-box;">$db</span>->createCommand(<span style="box-sizing: border-box;">'SELECT * FROM user LIMIT 10'</span>)->queryAll();

});

</code>

你也可以设置$db->enableSlaves 为false来使所有查询都在主服务器上执行.

操作数据库模式

获得模式信息

你可以通过 yii\db\Schema实例来获取Schema信息:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$schema</span> = <span style="box-sizing: border-box;">$connection</span>->getSchema();

</code>

该实例包括一系列方法来检索数据库多方面的信息:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">$tables</span> = <span style="box-sizing: border-box;">$schema</span>->getTableNames();

</code>

更多信息请参考yii\db\Schema

修改模式

除了基础的 SQL 查询,yii\db\Command还包括一系列方法来修改数据库模式:

  • 创建/重命名/删除/清空表
  • 增加/重命名/删除/修改字段
  • 增加/删除主键
  • 增加/删除外键
  • 创建/删除索引

使用示例:

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<code style="box-sizing: border-box; font-family: Menlo, Monaco, Consolas, 'Courier New', monospace; font-size: inherit; padding: 0px; color: inherit; border-radius: 0px; white-space: pre-wrap; background-color: transparent;"><span style="box-sizing: border-box;">// 创建表</span><span style="box-sizing: border-box;">$connection</span>->createCommand()->createTable(<span style="box-sizing: border-box;">'post'</span>, [

    <span style="box-sizing: border-box;">'id'</span> => <span style="box-sizing: border-box;">'pk'</span>,

    <span style="box-sizing: border-box;">'title'</span> => <span style="box-sizing: border-box;">'string'</span>,

    <span style="box-sizing: border-box;">'text'</span> => <span style="box-sizing: border-box;">'text'</span>,

]);

</code>

完整参考请查看yii\db\Command.