supabase-wrappers 0.1.26

Postgres Foreign Data Wrapper development framework in Rust.
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use crate::interface::Limit;
use pgrx::{FromDatum, is_a, pg_sys};

// extract limit
pub(crate) unsafe fn extract_limit(
    root: *mut pg_sys::PlannerInfo,
    _baserel: *mut pg_sys::RelOptInfo,
    _baserel_id: pg_sys::Oid,
) -> Option<Limit> {
    unsafe {
        let parse = (*root).parse;

        // don't push down LIMIT if the query has a GROUP BY clause or aggregates
        if !(*parse).groupClause.is_null() || (*parse).hasAggs {
            return None;
        }

        // only push down constant LIMITs that are not NULL
        let limit_count = (*parse).limitCount as *mut pg_sys::Const;
        if limit_count.is_null()
            || !is_a(limit_count as *mut pg_sys::Node, pg_sys::NodeTag::T_Const)
        {
            return None;
        }

        let mut limit = Limit::default();

        if let Some(count) = i64::from_polymorphic_datum(
            (*limit_count).constvalue,
            (*limit_count).constisnull,
            (*limit_count).consttype,
        ) {
            limit.count = count;
        } else {
            return None;
        }

        // only consider OFFSETS that are non-NULL constants
        let limit_offset = (*parse).limitOffset as *mut pg_sys::Const;
        if !limit_offset.is_null()
            && is_a(limit_offset as *mut pg_sys::Node, pg_sys::NodeTag::T_Const)
            && let Some(offset) = i64::from_polymorphic_datum(
                (*limit_offset).constvalue,
                (*limit_offset).constisnull,
                (*limit_offset).consttype,
            )
        {
            limit.offset = offset;
        }

        Some(limit)
    }
}