Trait QueryResultExt 

pub trait QueryResultExt<T> {
    // Required method
    fn downcast_err<E: Error + Send + Sync + 'static>(
        self,
    ) -> Result<Result<Arc<T>, TypedErr<E>>, QueryError>;
}

Extension trait for query results that provides ergonomic error downcasting.

This trait is implemented for Result<Arc<T>, QueryError> and allows you to downcast user errors to a specific type while propagating system errors.

Example

use query_flow::QueryResultExt;

// Downcast to MyError, propagating system errors and non-matching user errors
let result = db.query(MyQuery::new()).downcast_err::<MyError>()?;

match result {
    Ok(value) => println!("Success: {:?}", value),
    Err(my_err) => println!("MyError: {}", my_err.code),
}

Required Methods

fn downcast_err<E: Error + Send + Sync + 'static>( self, ) -> Result<Result<Arc<T>, TypedErr<E>>, QueryError>

Attempts to downcast a UserError to a specific error type.

Returns

• Ok(Ok(value)) - The query succeeded with value
• Ok(Err(typed_err)) - The query failed with a UserError of type E
• Err(query_error) - The query failed with a system error, or a UserError that is not of type E

Example

// Handle specific error type, propagate others
let result = db.query(MyQuery::new()).downcast_err::<MyError>()?;
let value = result.map_err(|e| {
    eprintln!("MyError occurred: {}", e.message);
    e
})?;

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementations on Foreign Types

impl<T> QueryResultExt<T> for Result<Arc<T>, QueryError>

fn downcast_err<E: Error + Send + Sync + 'static>( self, ) -> Result<Result<Arc<T>, TypedErr<E>>, QueryError>

Implementors