Trait TryIntoStruct

Source

pub trait TryIntoStruct {
    type Error;

    // Required method
    fn try_into_struct<S: DeserializeOwned>(self) -> Result<S, Self::Error>;
}

Expand description

Deserialize Trustfall query results or edge parameters into a Rust struct.

§Use with query results

Running a Trustfall query produces an iterator of BTreeMap<Arc<str>, FieldValue> outputs representing the query results. These maps all have a common “shape” — the same keys and the same value types — as determined by the query and schema.

This trait allows deserializing those query result maps into a dedicated struct, to get you easy access to strongly-typed data instead of FieldValue enums.

§Example

Say we ran a query like:

query {
    Order {
        item_name @output
        quantity @output
    }
}

Each of this query’s outputs contain a string named item_name and an integer named quantity. This trait allows us to define an output struct type:

#[derive(Debug, PartialEq, Eq, serde::Deserialize)]
struct Output {
    item_name: String,
    quantity: i64,
}

We can then unpack the query results into an iterator of such structs:


use trustfall_core::TryIntoStruct;

let results: Vec<_> = run_query()
    .expect("bad query arguments")
    .map(|v| v.try_into_struct().expect("struct definition did not match query result shape"))
    .collect();

assert_eq!(
    vec![
        Output {
            item_name: "widget".to_string(),
            quantity: 42,
        },
    ],
    results,
);

§Use with edge parameters

Edges defined in Trustfall schemas may take parameters, for example:

type NewsWebsite {
    latest_stories(count: Int!): [Story!]!
}

This trait can be used to deserialize &EdgeParameters into a struct specific to the parameters of that edge:

#[derive(Debug, PartialEq, Eq, serde::Deserialize)]
struct LatestStoriesParameters {
    count: usize
}

For example:


use trustfall_core::TryIntoStruct;

fn resolve_latest_stories(contexts: ContextIterator<Vertex>, parameters: &EdgeParameters) {
    let parameters: LatestStoriesParameters = parameters
        .try_into_struct()
        .expect("edge parameters did not match struct definition");
    let count = parameters.count;

    // then resolve the edge with the given count
}