# Transaction

> Represents a PostgreSQL DB transaction.

[API reference](/docs/api/index.md) › [yii](/docs/api/yii/index.md) › [db](/docs/api/yii/db/index.md) › [pgsql](/docs/api/yii/db/pgsql/index.md) › Transaction

| class | `yii\db\pgsql\Transaction` |
| --- | --- |
| Extends | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) » [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| Implements | [`yii\base\Configurable`](/docs/api/yii/base/configurable/index.md) |
| Since | 22.0 |
| Source | [`framework/db/pgsql/Transaction.php`](https://github.com/yiisoft/yii2/blob/22.0/framework/db/pgsql/Transaction.php#L28) |

Represents a PostgreSQL DB transaction.

PostgreSQL discards `SET TRANSACTION` issued outside a transaction block, so the isolation level is applied through
[`setIsolationLevel()`](/docs/api/yii/db/transaction/index.md#method-setIsolationLevel) right after the transaction starts, and the transaction is rolled back if the level is
rejected.

See also: <https://www.postgresql.org/docs/current/sql-set-transaction.html>.

## Properties

| Property | Type | Description | Defined by |
| --- | --- | --- | --- |
| <span id="property-db"></span>[`$db`](/docs/api/yii/db/transaction/index.md#property-db) | [`yii\db\Connection`](/docs/api/yii/db/connection/index.md) | The database connection that this transaction is associated with. Default: `null`. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="property-isActive"></span>[`$isActive`](/docs/api/yii/db/transaction/index.md#property-isActive) read-only | `bool` | Whether this transaction is active. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="property-isolationLevel"></span>[`$isolationLevel`](/docs/api/yii/db/transaction/index.md#property-isolationLevel) write-only | `string` | The transaction isolation level to use for this transaction. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="property-level"></span>[`$level`](/docs/api/yii/db/transaction/index.md#property-level) read-only | `int` | The current nesting level of the transaction. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |

## Methods

| Method | Description | Defined by |
| --- | --- | --- |
| <span id="method-__construct"></span>[`__construct()`](/docs/api/yii/base/baseobject/index.md#method-__construct) | Constructor. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__call"></span>[`__call()`](/docs/api/yii/base/baseobject/index.md#method-__call) | Calls the named method which is not a class method. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__get"></span>[`__get()`](/docs/api/yii/base/baseobject/index.md#method-__get) | Returns the value of an object property. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__isset"></span>[`__isset()`](/docs/api/yii/base/baseobject/index.md#method-__isset) | Checks if a property is set, i.e. defined and not null. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__set"></span>[`__set()`](/docs/api/yii/base/baseobject/index.md#method-__set) | Sets value of an object property. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__unset"></span>[`__unset()`](/docs/api/yii/base/baseobject/index.md#method-__unset) | Sets an object property to null. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| [`begin()`](#method-begin) | Begins a transaction. | `Transaction` |
| <span id="method-canGetProperty"></span>[`canGetProperty()`](/docs/api/yii/base/baseobject/index.md#method-canGetProperty) | Returns a value indicating whether a property can be read. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-canSetProperty"></span>[`canSetProperty()`](/docs/api/yii/base/baseobject/index.md#method-canSetProperty) | Returns a value indicating whether a property can be set. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-className"></span>[`className()`](/docs/api/yii/base/baseobject/index.md#method-className) static | Returns the fully qualified name of this class. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-commit"></span>[`commit()`](/docs/api/yii/db/transaction/index.md#method-commit) | Commits a transaction. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="method-getIsActive"></span>[`getIsActive()`](/docs/api/yii/db/transaction/index.md#method-getIsActive) | Returns a value indicating whether this transaction is active. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="method-getLevel"></span>[`getLevel()`](/docs/api/yii/db/transaction/index.md#method-getLevel) |  | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="method-hasMethod"></span>[`hasMethod()`](/docs/api/yii/base/baseobject/index.md#method-hasMethod) | Returns a value indicating whether a method is defined. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-hasProperty"></span>[`hasProperty()`](/docs/api/yii/base/baseobject/index.md#method-hasProperty) | Returns a value indicating whether a property is defined. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-init"></span>[`init()`](/docs/api/yii/base/baseobject/index.md#method-init) | Initializes the object. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-rollBack"></span>[`rollBack()`](/docs/api/yii/db/transaction/index.md#method-rollBack) | Rolls back a transaction. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="method-setIsolationLevel"></span>[`setIsolationLevel()`](/docs/api/yii/db/transaction/index.md#method-setIsolationLevel) | Sets the transaction isolation level for this transaction. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |

## Constants

| Constant | Value | Description | Defined by |
| --- | --- | --- | --- |
| <span id="const-READ_UNCOMMITTED"></span>[`READ_UNCOMMITTED`](/docs/api/yii/db/transaction/index.md#const-READ_UNCOMMITTED) | `'READ UNCOMMITTED'` | A constant representing the transaction isolation level `READ UNCOMMITTED`. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="const-READ_COMMITTED"></span>[`READ_COMMITTED`](/docs/api/yii/db/transaction/index.md#const-READ_COMMITTED) | `'READ COMMITTED'` | A constant representing the transaction isolation level `READ COMMITTED`. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="const-REPEATABLE_READ"></span>[`REPEATABLE_READ`](/docs/api/yii/db/transaction/index.md#const-REPEATABLE_READ) | `'REPEATABLE READ'` | A constant representing the transaction isolation level `REPEATABLE READ`. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |
| <span id="const-SERIALIZABLE"></span>[`SERIALIZABLE`](/docs/api/yii/db/transaction/index.md#const-SERIALIZABLE) | `'SERIALIZABLE'` | A constant representing the transaction isolation level `SERIALIZABLE`. | [`yii\db\Transaction`](/docs/api/yii/db/transaction/index.md) |

## Method details

### begin() <span id="method-begin"></span>

```php
public function begin(mixed $isolationLevel = null): mixed
```

Begins a transaction.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$isolationLevel` | `mixed` | The [isolation level][] to use for this transaction. This can be one of [`READ_UNCOMMITTED`](/docs/api/yii/db/transaction/index.md#const-READ_UNCOMMITTED), [`READ_COMMITTED`](/docs/api/yii/db/transaction/index.md#const-READ_COMMITTED), [`REPEATABLE_READ`](/docs/api/yii/db/transaction/index.md#const-REPEATABLE_READ) and [`SERIALIZABLE`](/docs/api/yii/db/transaction/index.md#const-SERIALIZABLE) but also a string containing DBMS specific syntax to be used after `SET TRANSACTION ISOLATION LEVEL`. If not specified (`null`) the isolation level will not be set explicitly and the DBMS default will be used. > Note: Some DBMS allow setting of the isolation level only for the whole connection so subsequent transactions may get the same isolation level even if you did not specify any. When using this feature you may need to set the isolation level for all transactions explicitly to avoid conflicting settings. At the time of this writing affected DBMS are MSSQL and SQLite. > Note: The isolation level applies to the outermost transaction only. Nested transactions are implemented with savepoints and always run at the isolation level of the outer transaction, so an `$isolationLevel` passed to a nested [`begin()`](/docs/api/yii/db/pgsql/transaction/index.md#method-begin) call is ignored and a warning is logged (since 2.0.56). [isolation level]: https://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Isolation_levels Starting from version 2.0.16, this method throws exception when beginning nested transaction and underlying DBMS does not support savepoints. |

**Returns**

`mixed`

**Throws**

- [`yii\base\InvalidConfigException`](/docs/api/yii/base/invalidconfigexception/index.md): if [`$db`](/docs/api/yii/db/transaction/index.md#property-db) is `null`
- [`yii\base\NotSupportedException`](/docs/api/yii/base/notsupportedexception/index.md): if the DBMS does not support nested transactions
- [`yii\db\Exception`](/docs/api/yii/db/exception/index.md): if DB connection fails