wpdb insert with prefix

### Example of `wpdb->insert()` with Table Prefix
Here's how you can insert data into a table using the `$wpdb->insert()` method:

global $wpdb;

// Table name with prefix
$table_name = $wpdb->prefix . 'your_table_name';

// Data to insert
$data = [
    'column1' => 'value1',
    'column2' => 'value2',
];

// Data format (optional, ensures proper data sanitization)
$format = ['%s', '%s']; // %s for strings, %d for integers, %f for floats

// Insert data into the table
$inserted = $wpdb->insert($table_name, $data, $format);

if ($inserted) {
    echo 'Data inserted successfully!';
} else {
    echo 'Failed to insert data.';
}

### Explanation
1. **`$wpdb->prefix`**: Automatically adds the correct table prefix (like `wp_` or any custom prefix you have set).
2. **Data Array**: The keys in the `$data` array should match the column names in your database table.
3. **Format Array**: The `$format` array is optional but recommended for security. It defines how each value should be treated (`%s` for strings, `%d` for integers, `%f` for floats).
4. **Error Handling**: `$wpdb->insert()` returns `false` on failure. You can use `$wpdb->last_error` to get more details in case of an error:

if (!$inserted) {
       echo 'Error: ' . $wpdb->last_error;
   }

### Example with `usermeta` Table (Prefix Included)
If you want to insert data into a core WordPress table like `usermeta`:

global $wpdb;

$meta_data = [
    'user_id'    => 1,
    'meta_key'   => 'custom_meta_key',
    'meta_value' => 'custom_value',
];

$meta_format = ['%d', '%s', '%s'];

$wpdb->insert($wpdb->prefix . 'usermeta', $meta_data, $meta_format);

This approach ensures that your code works regardless of the table prefix used in different WordPress installations.

Here's a robust way to get the user's IP address:

### Example Function to Get User IP Address

function get_user_ip() {
    if ( ! empty( $_SERVER['HTTP_CLIENT_IP'] ) ) {
        // Check for IP from shared internet
        $ip = $_SERVER['HTTP_CLIENT_IP'];
    } elseif ( ! empty( $_SERVER['HTTP_X_FORWARDED_FOR'] ) ) {
        // Check for IP passed from a proxy
        $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
        // In case of multiple IPs, take the first one
        $ip = explode( ',', $ip )[0];
    } else {
        // Default IP from remote address
        $ip = $_SERVER['REMOTE_ADDR'];
    }

    // Validate the IP address format
    return filter_var( $ip, FILTER_VALIDATE_IP ) ? $ip : 'Unknown';
}

// Usage Example
$user_ip = get_user_ip();
echo 'User IP: ' . esc_html( $user_ip );

### Explanation
1. **`HTTP_CLIENT_IP`**: Often used if the user is behind a proxy.
2. **`HTTP_X_FORWARDED_FOR`**: Commonly used for identifying the originating IP address of a client connecting through a proxy or load balancer.
– This header can contain a comma-separated list of IPs. The first one is usually the real IP.
3. **`REMOTE_ADDR`**: The default IP address set by the server.

### Important Security Note
– HTTP headers like `HTTP_CLIENT_IP` and `HTTP_X_FORWARDED_FOR` can be spoofed, so avoid using the user's IP for critical security checks.
– Always sanitize and validate the IP address using `filter_var()` with `FILTER_VALIDATE_IP`.

### Example in WordPress Context
You can use this function in your theme's `functions.php` file, a custom plugin, or within any template file where you need to display or use the user's IP address.

add_shortcode( 'show_user_ip', function() {
    return 'Your IP address is: ' . esc_html( get_user_ip() );
} );

You can then use the `[show_user_ip]` shortcode in any post or page to display the visitor's IP address.

### Syntax:

update_post_meta( int $post_id, string $meta_key, mixed $meta_value, mixed $prev_value = '' )

– **`$post_id`** (int): The ID of the post for which you want to update the meta.
– **`$meta_key`** (string): The key for the post meta.
– **`$meta_value`** (mixed): The new value for the post meta. This can be a string, array, or other data type.
– **`$prev_value`** (optional, mixed): The old value to check before updating. If specified, the update will only happen if the current value matches this one. This can be useful for preventing unnecessary updates.

### Example: Update Post Meta
Here's a simple example where we update a custom post meta value for a specific post:

$post_id = 123; // ID of the post you want to update
$meta_key = '_custom_meta_key'; // The meta key
$meta_value = 'New value'; // The new value you want to set

// Update the post meta
update_post_meta( $post_id, $meta_key, $meta_value );

### Example with Previous Value:
If you want to update the post meta only if the previous value matches a certain condition, you can use the `$prev_value` parameter:

$post_id = 123;
$meta_key = '_custom_meta_key';
$new_value = 'Updated value';
$old_value = 'Old value'; // The value that should be replaced

// Update only if the current value is 'Old value'
update_post_meta( $post_id, $meta_key, $new_value, $old_value );

### Check If Meta Exists Before Updating:
If you need to check if a meta key exists before updating, you can use `get_post_meta()`:

$post_id = 123;
$meta_key = '_custom_meta_key';

// Get the current meta value
$current_value = get_post_meta( $post_id, $meta_key, true );

// Only update if the value is different
if ( $current_value !== 'New value' ) {
    update_post_meta( $post_id, $meta_key, 'New value' );
}

### Important Notes:
– `update_post_meta()` will **not** update the post meta if the new value is the same as the existing value (unless the `$prev_value` is used).
– If the specified meta key does not exist, it will be added.
– Post meta values are stored in the `wp_postmeta` table in the database.

This function is useful for managing custom fields, settings, or any additional data associated with posts in WordPress.