Simple example of MongoDB usage with Actix Web. For more information on the MongoDB Rust driver, visit the [documentation](https://docs.rs/mongodb/2.0.0/mongodb/index.html) and [source code](https://github.com/mongodb/mongo-rust-driver).
The example code creates a client with the URI set by the `MONGODB_URI` environment variable. The default URI for a standalone `mongod` running on localhost is "mongodb://localhost:27017". For more information on MongoDB URIs, visit the [connection string](https://docs.mongodb.com/manual/reference/connection-string/) entry in the MongoDB manual.