Passing in arguments​

A regular EdgeQL query without arguments looks like this:

with
    message1 := 'Hello there',
    message2 := 'General Kenobi',
select message1 ++ ' ' ++ message2;

And the same query with arguments:

with
    message1 := <str>$0,
    message2 := <str>$1,
select message1 ++ ' ' ++ message2;

In the EdgeQL REPL you are prompted to enter arguments:

db> 
... 
... 
... 

with
message1 := <str>$0,
message2 := <str>$1,
select message1 ++ ' ' ++ message2;

Parameter <str>$0: Hello there
Parameter <str>$1: General Kenobi
{'Hello there General Kenobi'}

But when using the Rust client, there is no prompt to do so. At present, arguments also have to be in the order $0, $1, and so on, while in the REPL they can be named (e.g. $message and $person instead of $0 and $1). The arguments in the client are then passed to the appropriate query method as a tuple:

let args = ("Nice movie", 2023);
let query = "with
movie := (insert Movie {
title := <str>$0,
release_year := <int32>$1
})
select  {
    title,
    release_year,
    id
}";
let query_res: Value = client.query_required_single(query, &(args)).await?;

A note on the casting syntax: EdgeDB requires arguments to have a cast in the same way that Rust requires a type declaration in function signatures. As such, arguments in queries are used as type specification for the EdgeDB compiler, not to cast from queries from the Rust side. Take this query as an example:

let query = "select <int32>$0";

This simply means “select an argument that must be an int32”, not “take the received argument and cast it into an int32”.

As such, this will return an error:

let query = "select <int32>$0";
let arg = 9i16; // Rust client will expect an int16
let query_res: Result<Value, _> =
  client.query_required_single(query, &(arg,)).await;
assert!(query_res
    .unwrap_err()
    .to_string()
    .contains("expected std::int16"));