Resolving PDO::exec() Parameters Error in MySQL Insertion Queries

Learn how to fix the common error "PDO::exec() expects exactly 1 parameter, 2 given" in your PHP application when performing database insertions using PDO.
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Understanding and Fixing the PDO::exec() Parameters Error

If you're working with PHP and PDO to interact with a MySQL database, you may have encountered the frustrating error message: "PDO::exec() expects exactly 1 parameter, 2 given." This error can halt your application and leave you scratching your head, especially if you're just starting with PHP and database interactions.

In this guide, we'll explain what causes this error and provide a step-by-step guide on how to resolve it effectively. We'll use a common scenario of scanning a directory and inserting the file names into a MariaDB table. Let’s dive in!

The Problem: What Does the Error Mean?

The error you're facing indicates that the PDO::exec() method is trying to accept more parameters than it is designed to handle. In short, exec() only takes one argument: a SQL statement as a string. If you attempt to pass multiple parameters to it, you'll receive the error message noted above.

The Line Causing the Error

In the provided PHP code, the error occurs at this line:

[[See Video to Reveal this Text or Code Snippet]]

Here, you are attempting to insert two parameters ($key and $parentId) into the database using exec(), which is not the correct approach.

The Solution: Use Prepared Statements

To fix this issue, you'll need to switch from using exec() to using prepared statements with prepare() and execute(). Prepared statements not only help avoid errors like this but also enhance security against SQL injection.

Step-by-Step Guide to Fix the Code

Prepare the SQL Statement:
Rather than calling exec(), you should prepare your SQL statement. This allows you to define placeholders and bind values to those placeholders later.

Using Execute:
After preparing the statement, use the execute() method to run the prepared statement with the respective parameters.

Retrieve Last Insert ID:
Instead of using fetch() with a query to retrieve the last inserted ID, you can use the lastInsertId() method.

Here’s how your revised function dirToDb will look like:

[[See Video to Reveal this Text or Code Snippet]]

Key Points

Use prepare(): Always prepare your SQL statements ahead of executing them.

Use execute(): This method handles the parameters correctly, allowing you to pass them as an array.

Retrieve with lastInsertId(): Simplifies accessing the ID of the last inserted row without needing an additional query.

Conclusion

By following these steps, you’ll not only solve the PDO::exec() error but also adhere to best practices in database handling within PHP. Shifting to prepared statements makes your code cleaner, more secure, and much less error-prone. If you have further questions or run into other issues while coding, feel free to reach out. Happy coding!