What Are the Common Reasons for mysqli_stmt::attr_get Function Returning False?

When performing database operations using PHP's mysqli extension, the mysqli_stmt::attr_get function is used to retrieve the attribute values of a prepared statement (mysqli_stmt). This function can return false in certain cases, which usually indicates a failure in retrieving the attribute. This article will analyze the common reasons why mysqli_stmt::attr_get returns false and provide corresponding solutions.

1. Using Unsupported Attribute Constants

mysqli_stmt::attr_get requires a valid attribute constant as a parameter, such as MYSQLI_STMT_ATTR_UPDATE_MAX_LENGTH. If an invalid or undefined attribute constant is passed, the function will return false.

Example:

$mysqli = new mysqli('m66.net', 'user', 'pass', 'database');
$stmt = $mysqli->prepare("SELECT * FROM users WHERE id = ?");
$stmt->bind_param("i", $id);
<p>$attr = $stmt->attr_get(9999); // Invalid attribute constant<br>
if ($attr === false) {<br>
echo "Failed to retrieve attribute, the attribute constant is invalid or unsupported.";<br>
}<br>

Recommendation: Please refer to the official documentation to ensure that the attribute constant is correct and supported.

2. Prepared Statement Object Not Properly Initialized or Closed

If the $stmt object was not successfully created or has already been closed with $stmt->close(), calling attr_get will fail.

Example:

$stmt = $mysqli->prepare("SELECT * FROM users WHERE id = ?");
if (!$stmt) {
    die("Failed to prepare statement: " . $mysqli->error);
}
$stmt->close();
<p>$attr = $stmt->attr_get(MYSQLI_STMT_ATTR_UPDATE_MAX_LENGTH);<br>
if ($attr === false) {<br>
echo "Failed to retrieve attribute, prepared statement object is unavailable.";<br>
}<br>

Recommendation: Ensure that the prepared statement object is valid and not closed before calling attr_get.

3. Database Driver or PHP Version Compatibility Issues

Certain PHP versions or MySQL driver versions may have compatibility issues, causing attr_get to malfunction and return false.

Recommendation:

• Ensure that both PHP and MySQL versions are the official recommended stable versions.

• Try upgrading to the latest versions of PHP and MySQL.

• Test in different environments to rule out environmental issues.

4. Incorrect Attribute Parameter Type

attr_get requires the attribute parameter to be an integer constant. If a string or other type is passed, the function may return false.

Example:

$attr = $stmt->attr_get("MYSQLI_STMT_ATTR_UPDATE_MAX_LENGTH"); // Incorrect usage
if ($attr === false) {
    echo "Failed to retrieve attribute, incorrect parameter type.";
}

Recommendation: Ensure the parameter is a predefined integer constant.

5. Database Connection or Resource Errors

In rare cases, database connection issues or resource state problems can also cause the function to return false.

Recommendation:

• Ensure a stable database connection.

• Catch and handle possible exceptions or errors.

• Use $mysqli->error and $stmt->error to get detailed error information.

Code Example Summary

Below is a correct usage example of mysqli_stmt::attr_get:

$mysqli = new mysqli('m66.net', 'user', 'pass', 'database');
if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}
<p>$stmt = $mysqli->prepare("SELECT * FROM users WHERE id = ?");<br>
if (!$stmt) {<br>
die("Failed to prepare statement: " . $mysqli->error);<br>
}</p>
<p>$id = 1;<br>
$stmt->bind_param("i", $id);</p>
<p>$attr = $stmt->attr_get(MYSQLI_STMT_ATTR_UPDATE_MAX_LENGTH);<br>
if ($attr === false) {<br>
echo "Failed to retrieve attribute, error message: " . $stmt->error;<br>
} else {<br>
echo "Attribute value: " . $attr;<br>
}</p>
<p data-is-last-node="" data-is-only-node="">$stmt->close();<br>
$mysqli->close();<br>