kip-sql 0.0.1-alpha.8

build the SQL layer of KipDB database
Documentation 
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use crate::execution::volcano::{BoxedExecutor, Executor};
use crate::execution::ExecutorError;
use crate::expression::ScalarExpression;
use crate::planner::operator::project::ProjectOperator;
use crate::storage::Transaction;
use crate::types::tuple::Tuple;
use futures_async_stream::try_stream;
use std::cell::RefCell;

pub struct Projection {
    exprs: Vec<ScalarExpression>,
    input: BoxedExecutor,
}

impl From<(ProjectOperator, BoxedExecutor)> for Projection {
    fn from((ProjectOperator { exprs }, input): (ProjectOperator, BoxedExecutor)) -> Self {
        Projection { exprs, input }
    }
}

impl<T: Transaction> Executor<T> for Projection {
    fn execute<'a>(self, _transaction: &RefCell<T>) -> BoxedExecutor {
        self._execute()
    }
}

impl Projection {
    #[try_stream(boxed, ok = Tuple, error = ExecutorError)]
    pub async fn _execute(self) {
        let Projection { exprs, input } = self;

        #[for_await]
        for tuple in input {
            let mut tuple = tuple?;

            let mut columns = Vec::with_capacity(exprs.len());
            let mut values = Vec::with_capacity(exprs.len());

            for expr in exprs.iter() {
                values.push(expr.eval(&tuple)?);
                columns.push(expr.output_column());
            }

            tuple.columns = columns;
            tuple.values = values;

            yield tuple;
        }
    }
}