datafusion/catalog/src/cte_worktable.rs

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//! CteWorkTable implementation used for recursive queries

use std::sync::Arc;
use std::{any::Any, borrow::Cow};

use crate::Session;
use arrow::datatypes::SchemaRef;
use async_trait::async_trait;
use datafusion_physical_plan::work_table::WorkTableExec;

use datafusion_physical_plan::ExecutionPlan;

use datafusion_common::error::Result;
use datafusion_expr::{Expr, LogicalPlan, TableProviderFilterPushDown, TableType};

use crate::TableProvider;

/// The temporary working table where the previous iteration of a recursive query is stored
/// Naming is based on PostgreSQL's implementation.
/// See here for more details: www.postgresql.org/docs/11/queries-with.html#id-1.5.6.12.5.4
#[derive(Debug)]
pub struct CteWorkTable {
    /// The name of the CTE work table
    name: String,
    /// This schema must be shared across both the static and recursive terms of a recursive query
    table_schema: SchemaRef,
}

impl CteWorkTable {
    /// construct a new CteWorkTable with the given name and schema
    /// This schema must match the schema of the recursive term of the query
    /// Since the scan method will contain an physical plan that assumes this schema
    pub fn new(name: &str, table_schema: SchemaRef) -> Self {
        Self {
            name: name.to_owned(),
            table_schema,
        }
    }

    /// The user-provided name of the CTE
    pub fn name(&self) -> &str {
        &self.name
    }

    /// The schema of the recursive term of the query
    pub fn schema(&self) -> SchemaRef {
        Arc::clone(&self.table_schema)
    }
}

#[async_trait]
impl TableProvider for CteWorkTable {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn get_logical_plan(&'_ self) -> Option<Cow<'_, LogicalPlan>> {
        None
    }

    fn schema(&self) -> SchemaRef {
        Arc::clone(&self.table_schema)
    }

    fn table_type(&self) -> TableType {
        TableType::Temporary
    }

    async fn scan(
        &self,
        _state: &dyn Session,
        _projection: Option<&Vec<usize>>,
        _filters: &[Expr],
        _limit: Option<usize>,
    ) -> Result<Arc<dyn ExecutionPlan>> {
        // TODO: pushdown filters and limits
        Ok(Arc::new(WorkTableExec::new(
            self.name.clone(),
            Arc::clone(&self.table_schema),
        )))
    }

    fn supports_filters_pushdown(
        &self,
        filters: &[&Expr],
    ) -> Result<Vec<TableProviderFilterPushDown>> {
        // TODO: should we support filter pushdown?
        Ok(vec![
            TableProviderFilterPushDown::Unsupported;
            filters.len()
        ])
    }
}