async-graphql/docs/en/src/define_complex_object.md

Object

Different from SimpleObject, Object must have Resolve defined for each field in impl.

A resolver function has to be asynchronous. The first argument has to be &self, second being optional Context and followed by field arguments.

Resolve is used to get the value of the field. You can query a database and return the result. The return type of the function is the type of the field. You can also return a async_graphql::FieldResult so to return an error if it occrs and error message will be send to query result.

When querying a database, you may need a global data base connection pool. When creating Schema, you can use SchemaBuilder::data to setup Schema data, and Context::data to setup Contextdata. The following value_from_db function showed how to retrive a database connection from Context.

use async_graphql::*;

struct MyObject {
    value: i32,
}

#[Object]
impl MyObject {
    async fn value(&self) -> String {
        self.value.to_string()
    }

    async fn value_from_db(
        &self,
        ctx: &Context<'_'>,
        #[arg(desc = "Id of object")] id: i64
    ) -> FieldResult<String> {
        let conn = ctx.data::<DbPool>().take();
        Ok(conn.query_something(id)?.name)
    }
}