Trait trustfall_core::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
}