Serialize FlashCard

We have modeled flash cards on the server. We now need to turn it into JSON before we can send it to the client.

In this chapter we will use serde to automatically serialize our flash cards.

Dependency

We will need two dependencies that we need to list in our Cargo.toml. Together they allow us to serialize flash cards into JSON. Add serde and serde_json to the dependencies table in Cargo.toml.

serde = { version = "1.0.101", features = [ "derive" ] }
sserde_json = "1.0.41"

Use serde

In order to leverage the serialization capabilities of serde_json we need to create a serde serializer. There is a very cool trick that serde knows that makes this a breeze.

The first thing we need to do is to announce we our needing serde.

# #![allow(unused_variables)]
#fn main() {
use serde::Serialize;
#}

The other thing is that we need to tell serde that we would like it to derive serializers for our data types. We can do this by annotating both FlashCard and Face with a derive annotation. E.g. Face would be annotated like

# #![allow(unused_variables)]
#fn main() {
#[derive(Serialize)]
pub enum Face {
    Front,
    Back,
}
#}

Verification

With the automatic part of serde done, it is good to see if serialization works like we expect. The best way to do this is to test is. Rust integrates testing right at the place where the source is created. Add the following code at the end of src/domain/mod.rs.

# #![allow(unused_variables)]
#fn main() {
#[cfg(test)]
mod test {
    use super::*;
    use serde_json;

    #[test]
    fn flash_card_can_be_serialized_to_json() {
        let flash_card = FlashCard::new("Wettervorhersage", "Weather forecast");

        let actual = serde_json::to_string(&flash_card).unwrap();

        let expected = r#"{"front":"Wettervorhersage","back":"Weather forecast","face":"Front"}"#.to_owned();
        assert_eq!(actual, expected);
    }
}
#}

There is some boilerplate to let the test framework know about what we want to test. The actual test is

# #![allow(unused_variables)]
#fn main() {
        let flash_card = FlashCard::new("Wettervorhersage", "Weather forecast");

        let actual = serde_json::to_string(&flash_card).unwrap();

        let expected = r#"{"front":"Wettervorhersage","back":"Weather forecast","face":"Front"}"#.to_owned();
        assert_eq!(actual, expected);
#}

It creates a FlashCard, serializes it to JSON with serde_json, sets up an expectation, and checks it the expectation is met.

If you run

cargo test

it should give the all green.