Using your generated queries

Once you have written your queries and generated your Rust code with Cornucopia, it's time to use them. Hurray 🎉!

Let's say you have generated your Rust module into src/cornucopia.rs, then this is as simple as importing the items you need from it, like so:

mod cornucopia;

use cornucopia::authors;

Building the query object

Building a query object starts with either the query function:

authors().bind(&client, Some("Greece"));

or the generated parameter struct:

use cornucopia_async::Params;

authors().params(
    &client, 
    AuthorsParams {
        country: Some("Greece")
    }
);

The query function is useful when you have a few obvious parameters, while the parameter struct is more explicit.

Note that in order to use the params method, you need to import the Params trait from your (sync or async) cornucopia client.

Row mapping (optional)

Query objects have a map method that allows them to transform the query's returned rows without requiring intermediate allocation. The following example is pretty contrived but illustrates how you can use this feature.

enum Country {
    Greece,
    TheRest
}

impl<'a> From<&'a str> for Country {
    fn from(s: &'a str) -> Self {
        if s == "Greece" {
            Self::Greece
        } else {
            Self::TheRest
        }
    }
}

struct CustomAuthor {
    full_name: String,
    country: Country,
    age: usize,
}

authors()
    .bind(&client)
    .map(|author| {
        let full_name = format!(
            "{}, {}",
            author.last_name.to_uppercase(),
            author.first_name
        );
        let country = Country::from(author.country);
        CustomAuthor {
            full_name,
            country,
            age: author.age,
        }
    });

The result of a map is another query object.

Getting rows out of your queries

Once the query object has been built, use one of the following methods to select the expected number of rows:

• opt: one or zero rows (error otherwise).
• one: exactly one row (error otherwise).
• iter: iterator of zero or more rows.
• all: like iter, but collects the rows in a Vec.

Here are some example uses:

author_by_id().bind(&client, &0).opt().await?;
author_by_id().bind(&client, &0).one().await?; // Error if this author id doesn't exist
authors().bind(&client).all().await?;
authors().bind(&client).iter().await?.collect::<Vec<_>>(); // Acts the same as the previous line