Created
August 20, 2022 18:16
-
-
Save rj76/05a91b548ca19d395d65e313f52d6c89 to your computer and use it in GitHub Desktop.
Function to create a subselect so it can be used in Diesel's select()
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
use diesel::prelude::*; | |
use diesel::backend::Backend; | |
use diesel::expression::{Expression, AsExpression, Selectable, ValidGrouping}; | |
use diesel::query_builder::{AstPass, Query, QueryFragment}; | |
use diesel::{QueryResult}; | |
use diesel::pg::Pg; | |
use diesel::sql_types::{SingleValue}; | |
use crate::schema::{order_order, order_status}; | |
pub struct Subquery<T> { | |
subquery: T, | |
alias: String, | |
} | |
impl<T> QueryFragment<Pg> for Subquery<T> | |
where | |
T: QueryFragment<Pg>, | |
{ | |
fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, Pg>) -> QueryResult<()> { | |
self.subquery.walk_ast(out.reborrow())?; | |
out.push_sql(" AS "); | |
out.push_identifier(self.alias.as_str()).expect("Error adding alias"); | |
Ok(()) | |
} | |
} | |
impl<T> Expression for Subquery<T> | |
where T: Expression | |
{ | |
type SqlType = T::SqlType; | |
} | |
impl<T> AppearsOnTable<order_order::table> for Subquery<T> | |
where T: Expression | |
{} | |
impl<T> SelectableExpression<order_order::table> for Subquery<T> | |
where T: Expression | |
{} | |
impl<T, GB> ValidGrouping<GB> for Subquery<T> | |
where T: Expression + ValidGrouping<GB> | |
{ | |
type IsAggregate = T::IsAggregate; | |
} | |
impl<T, DB: Backend> Selectable<DB> for Subquery<T> | |
where T: QueryFragment<DB> + Expression + Selectable<DB> | |
{ | |
type SelectExpression = order_status::id; | |
fn construct_selection() -> Self::SelectExpression { | |
order_status::id | |
} | |
} | |
pub fn get_subquery_for_select<T>(subquery: T, alias: String) -> Subquery<T> { | |
Subquery { | |
subquery, | |
alias | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment