Why does `mysqli_query()` return a 'Warning: mysqli_query() expects parameter 1 to be mysqli, null given' error?

Warning: Understanding mysqli_query() Parameter Error

When using mysqli_query() in PHP, it's crucial to ensure that the first parameter is a valid mysqli object representing a database connection. However, if you encounter an error stating "Warning: mysqli_query() expects parameter 1 to be mysqli, null given in," it indicates that the first parameter passed to the function is not a mysqli object.

Examining the Code

In your provided code, you have a function called getPosts(). This function attempts to query a database table named Blog. However, in the mysqli_query() call within getPosts(), the first parameter is not explicitly passed. As a result, PHP assumes the value of $con, which is declared outside the function, as the first parameter. But, $con is not in the scope of getPosts() and hence returns null.

Resolving the Error

To resolve this issue, you have two options:

1. **Globalize the $con Variable:** You can make the $con variable global inside getPosts() using the global $con; declaration. This will tell PHP to look for $con outside the function, making it accessible within getPosts().
2. **Pass the $con Variable as a Parameter:** A better approach is to pass the $con object as a parameter to the getPosts() function. This ensures that getPosts() has direct access to the database connection, eliminating the need for global scope.

Example:

function getPosts(mysqli $con) {
    // ... same code as before
}

// Connect to the database
$con = mysqli_connect("localhost", "xxxx", "xxxx", "xxxxx");
// Call getPosts() with the connection as a parameter
getPosts($con);

Additional Recommendations

It's also advisable to handle any potential errors that may occur during database operations. You can enable error reporting explicitly as follows:

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); // throw exceptions

This will throw exceptions if any errors occur, allowing you to take appropriate action in your code.

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