How to Pass a Mutable Reference of a MySQL Connection in a Rust Struct

Learn how to manage a MySQL database connection efficiently in Rust by passing around a mutable reference to a connection struct.
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Efficiently Passing a MySQL Connection in a Rust Struct

Managing database connections can be intricate, especially when working with a programming language like Rust that emphasizes safety and concurrency. If you're building a Rust application and need to interact with a MySQL database, you might find yourself facing a common challenge: how to pass around a reference to a MySQL connection in a struct. This guide will guide you through the steps to achieve this efficiently and correctly.

The Problem Scenario

You have created a structure (DB) that contains a MySQL connection (PooledConn). You want to be able to reuse this connection across different functions without reopening a new connection each time. Let's say you have set up your DB struct and initialized it correctly, as shown in the following snippet:

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

This correctly creates a database connection and uses it to perform queries. However, when you attempt to pass your DB struct around, you encounter a compiler error.

Understanding the Compiler Error

When you try to pass your DB instance as a mutable reference to your query function like this:

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

You're facing an issue. Although you've declared db as mutable, it is still an immutable reference to the db::DB. This means you can't perform mutable operations (like executing queries) on it. The Rust compiler raises an error saying that db is a reference type and cannot be borrowed as mutable.

The Solution

To solve this issue, you simply need to change the function signature of your query method to accept a mutable reference. Here’s how to do it:

Change the function signature to accept a mutable reference of db::DB:

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

Rewrite the call to query, ensuring you pass the mutable reference:

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

This approach allows you to perform query operations that modify the internal state of the database connection.

Example Code Implementation

Here’s the complete working example with the modifications:

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

Conclusion

By simply passing a mutable reference to your DB struct, you can efficiently manage a single MySQL connection throughout your Rust application. This lets you perform multiple queries without the overhead of creating new connections each time, optimizing your program's performance and efficiency.

Now you can confidently work with MySQL connections in Rust while leveraging the language's strong type system and memory safety principles. Happy coding!