get_option

get_option函数是一个WordPress函数，它从数据库中检索一个选项值。WordPress中的选项是可以由用户设置和调整的设置: 这个函数接受一个参数，它是你想检索的选项的名称。例如，如果你想检索”blogname”选项的值，你会调用get_option(‘blogname’): 该函数返回该选项的值。

检索基于选项名称的选项值。

如果该选项不存在，并且没有提供默认值。会返回布尔值false。这可以用来检查你是否需要 在安装插件的过程中初始化一个选项，然而这 可以通过使用add_option()更好地完成，它将不会覆盖 现有的选项。

不初始化一个选项并使用布尔值”false”作为返回值 是一个不好的做法，因为它会触发一个额外的数据库查询。

返回值的类型可以与保存或更新选项时传递的类型不同。时传递的类型不同。如果选项的值被序列化了。那么当它被返回时，它将被取消序列化。在这种情况下，其类型将 是相同的。例如，存储一个像数组一样的非标量值会 返回相同的数组。

在大多数情况下，非字符串的标量值和空值将被转换并返回 作为字符串的等价物。

例外的情况：

1. 当选项没有保存在数据库中时，如果提供了”$default”值，就会返回。会被返回。如果没有，将返回布尔值`false`。
2. 当使用选项API过滤器之一时。{@see ‘pre_option_$option’}, {@see ‘default_option_$option’}, or {@see ‘option_$option’}, the return 值可能不符合预期的类型。
3. 当选项刚刚被保存在数据库中，并且get_option() 之后，非字符串的标量值和空值不会被转换为等同于字符串的值。字符串等价物，并返回原始类型。

示例：

当像这样添加选项时。`add_option( ‘my_option_name’, ‘value’)`这样添加选项时。然后用`get_option( ‘my_option_name’)`来获取它们，返回的 返回的值将是：

– `false` returns `string(0)””`
– `true` returns `string(1)”1″`
– `0` returns `string(1)”0″`
– `1` returns `string(1)”1″`
– `’0’` returns `string(1)”0″`
– `’1’` returns `string(1)”1″`
– `null` returns `string(0)””`

当添加非标量值的选项时，如 `add_option( ‘my_array’, array( false, ‘str’, null )`, 返回值 将与原始值相同，因为它在保存到数据库之前被序列化了 它被序列化后保存在数据库中：

array(3) {
[0] => bool(false)
[1] => string(3)”str”
[2] => NULL
}

function get_option( $option, $default = false ) {
	global $wpdb;

	if ( is_scalar( $option ) ) {
		$option = trim( $option );
	}

	if ( empty( $option ) ) {
		return false;
	}

	/*
	 * Until a proper _deprecated_option() function can be introduced,
	 * redirect requests to deprecated keys to the new, correct ones.
	 */
	$deprecated_keys = array(
		'blacklist_keys'    => 'disallowed_keys',
		'comment_whitelist' => 'comment_previously_approved',
	);

	if ( isset( $deprecated_keys[ $option ] ) && ! wp_installing() ) {
		_deprecated_argument(
			__FUNCTION__,
			'5.5.0',
			sprintf(
				/* translators: 1: Deprecated option key, 2: New option key. */
				__( 'The "%1$s" option key has been renamed to "%2$s".' ),
				$option,
				$deprecated_keys[ $option ]
			)
		);
		return get_option( $deprecated_keys[ $option ], $default );
	}

	/**
	 * Filters the value of an existing option before it is retrieved.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * Returning a value other than false from the filter will short-circuit retrieval
	 * and return that value instead.
	 *
	 * @since 1.5.0
	 * @since 4.4.0 The `$option` parameter was added.
	 * @since 4.9.0 The `$default` parameter was added.
	 *
	 * @param mixed  $pre_option The value to return instead of the option value. This differs
	 *                           from `$default`, which is used as the fallback value in the event
	 *                           the option doesn't exist elsewhere in get_option().
	 *                           Default false (to skip past the short-circuit).
	 * @param string $option     Option name.
	 * @param mixed  $default    The fallback value to return if the option does not exist.
	 *                           Default false.
	 */
	$pre = apply_filters( "pre_option_{$option}", false, $option, $default );

	/**
	 * Filters the value of all existing options before it is retrieved.
	 *
	 * Returning a truthy value from the filter will effectively short-circuit retrieval
	 * and return the passed value instead.
	 *
	 * @since 6.1.0
	 *
	 * @param mixed  $pre_option  The value to return instead of the option value. This differs
	 *                            from `$default`, which is used as the fallback value in the event
	 *                            the option doesn't exist elsewhere in get_option().
	 *                            Default false (to skip past the short-circuit).
	 * @param string $option      Name of the option.
	 * @param mixed  $default     The fallback value to return if the option does not exist.
	 *                            Default false.
	 */
	$pre = apply_filters( 'pre_option', $pre, $option, $default );

	if ( false !== $pre ) {
		return $pre;
	}

	if ( defined( 'WP_SETUP_CONFIG' ) ) {
		return false;
	}

	// Distinguish between `false` as a default, and not passing one.
	$passed_default = func_num_args() > 1;

	if ( ! wp_installing() ) {
		// Prevent non-existent options from triggering multiple queries.
		$notoptions = wp_cache_get( 'notoptions', 'options' );

		// Prevent non-existent `notoptions` key from triggering multiple key lookups.
		if ( ! is_array( $notoptions ) ) {
			$notoptions = array();
			wp_cache_set( 'notoptions', $notoptions, 'options' );
		}

		if ( isset( $notoptions[ $option ] ) ) {
			/**
			 * Filters the default value for an option.
			 *
			 * The dynamic portion of the hook name, `$option`, refers to the option name.
			 *
			 * @since 3.4.0
			 * @since 4.4.0 The `$option` parameter was added.
			 * @since 4.7.0 The `$passed_default` parameter was added to distinguish between a `false` value and the default parameter value.
			 *
			 * @param mixed  $default The default value to return if the option does not exist
			 *                        in the database.
			 * @param string $option  Option name.
			 * @param bool   $passed_default Was `get_option()` passed a default value?
			 */
			return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
		}

		$alloptions = wp_load_alloptions();

		if ( isset( $alloptions[ $option ] ) ) {
			$value = $alloptions[ $option ];
		} else {
			$value = wp_cache_get( $option, 'options' );

			if ( false === $value ) {
				$row = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );

				// Has to be get_row() instead of get_var() because of funkiness with 0, false, null values.
				if ( is_object( $row ) ) {
					$value = $row->option_value;
					wp_cache_add( $option, $value, 'options' );
				} else { // Option does not exist, so we must cache its non-existence.
					if ( ! is_array( $notoptions ) ) {
						$notoptions = array();
					}

					$notoptions[ $option ] = true;
					wp_cache_set( 'notoptions', $notoptions, 'options' );

					/** This filter is documented in wp-includes/option.php */
					return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
				}
			}
		}
	} else {
		$suppress = $wpdb->suppress_errors();
		$row      = $wpdb->get_row( $wpdb->prepare( "SELECT option_value FROM $wpdb->options WHERE option_name = %s LIMIT 1", $option ) );
		$wpdb->suppress_errors( $suppress );

		if ( is_object( $row ) ) {
			$value = $row->option_value;
		} else {
			/** This filter is documented in wp-includes/option.php */
			return apply_filters( "default_option_{$option}", $default, $option, $passed_default );
		}
	}

	// If home is not set, use siteurl.
	if ( 'home' === $option && '' === $value ) {
		return get_option( 'siteurl' );
	}

	if ( in_array( $option, array( 'siteurl', 'home', 'category_base', 'tag_base' ), true ) ) {
		$value = untrailingslashit( $value );
	}

	/**
	 * Filters the value of an existing option.
	 *
	 * The dynamic portion of the hook name, `$option`, refers to the option name.
	 *
	 * @since 1.5.0 As 'option_' . $setting
	 * @since 3.0.0
	 * @since 4.4.0 The `$option` parameter was added.
	 *
	 * @param mixed  $value  Value of the option. If stored serialized, it will be
	 *                       unserialized prior to being returned.
	 * @param string $option Option name.
	 */
	return apply_filters( "option_{$option}", maybe_unserialize( $value ), $option );
}