The Queryable macro is the recommended way to make EdgeDB queries in
Rust, but some alternatives exist.
Value enumThe Value enum can be found in the edgedb-protocol crate. A Value
represents anything returned from EdgeDB. This means you can always return
a Value from any of the query methods without needing to deserialize
into a Rust type, and the enum can be instructive in getting to know
the protocol. On the other hand, returning a Value leads to
pattern matching to get to the inner value and is not the most ergonomic way
to work with results from EdgeDB.
pub enum Value {
Nothing,
Uuid(Uuid),
Str(String),
Bytes(Vec<u8>),
Int16(i16),
Int32(i32),
Int64(i64),
Float32(f32),
Float64(f64),
BigInt(BigInt),
// ... and so on
}Most variants of the Value enum correspond to a Rust type from the Rust
standard library, while some are from the edgedb-protocol crate and must
be constructed. For example, this query expecting an EdgeDB bigint will
return an error as it receives a 20, which is an i32:
let query = "select <bigint>$0";
let arg = 20;
let query_res: Result<Value, _> =
client.query_required_single(query, &(arg,)).await;
assert!(format!("{query_res:?}").contains("expected std::int32"));Instead, first construct a BigInt from the i32 and pass that in
as an argument:
use edgedb_protocol::model::BigInt;
let query = "select <bigint>$0";
let arg = BigInt::from(20);
let query_res: Result<Value, _> =
client.query_required_single(query, &(arg,)).await;
assert_eq!(
format!("{query_res:?}"),
"Ok(BigInt(BigInt { negative: false, weight: 0, digits: [20] }))"
);EdgeDB can cast any type to JSON with <json>, but the *_json methods
don’t require this cast in the query. This result can be turned into a
String and used to respond to some JSON API request directly, unpacked
into a struct using serde and serde_json, etc.
#[derive(Debug, Deserialize)]
pub struct Account {
pub username: String,
pub id: Uuid,
}
// No need for <json> cast here
let query = "select Account {
username,
id
} filter .username = <str>$0;";
// Can use query_single_json if we know there will only be one result;
// otherwise query_json which returns a map of json
let json_res = client
.query_single_json(query, &("SomeUserName",))
.await?
.unwrap();
// Format:
// {"username" : "SomeUser1",
// "id" : "7093944a-fd3a-11ed-a013-c7de12ffe7a9"}
let as_string = json_res.to_string();
let as_account: Account = serde_json::from_str(&json_res)?;