plan.rs

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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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//! Tree node implementation for logical plan

use crate::LogicalPlan;
use datafusion_common::tree_node::{TreeNodeVisitor, VisitRecursion};
use datafusion_common::{tree_node::TreeNode, Result};
use std::borrow::Cow;

impl TreeNode for LogicalPlan {
    fn children_nodes(&self) -> Vec<Cow<Self>> {
        self.inputs().into_iter().map(Cow::Borrowed).collect()
    }

    fn apply<F>(&self, op: &mut F) -> Result<VisitRecursion>
    where
        F: FnMut(&Self) -> Result<VisitRecursion>,
    {
        // Note,
        //
        // Compared to the default implementation, we need to invoke
        // [`Self::apply_subqueries`] before visiting its children
        match op(self)? {
            VisitRecursion::Continue => {}
            // If the recursion should skip, do not apply to its children. And let the recursion continue
            VisitRecursion::Skip => return Ok(VisitRecursion::Continue),
            // If the recursion should stop, do not apply to its children
            VisitRecursion::Stop => return Ok(VisitRecursion::Stop),
        };

        self.apply_subqueries(op)?;

        self.apply_children(&mut |node| node.apply(op))
    }

    /// To use, define a struct that implements the trait [`TreeNodeVisitor`] and then invoke
    /// [`LogicalPlan::visit`].
    ///
    /// For example, for a logical plan like:
    ///
    /// ```text
    /// Projection: id
    ///    Filter: state Eq Utf8(\"CO\")\
    ///       CsvScan: employee.csv projection=Some([0, 3])";
    /// ```
    ///
    /// The sequence of visit operations would be:
    /// ```text
    /// visitor.pre_visit(Projection)
    /// visitor.pre_visit(Filter)
    /// visitor.pre_visit(CsvScan)
    /// visitor.post_visit(CsvScan)
    /// visitor.post_visit(Filter)
    /// visitor.post_visit(Projection)
    /// ```
    fn visit<V: TreeNodeVisitor<N = Self>>(
        &self,
        visitor: &mut V,
    ) -> Result<VisitRecursion> {
        // Compared to the default implementation, we need to invoke
        // [`Self::visit_subqueries`] before visiting its children

        match visitor.pre_visit(self)? {
            VisitRecursion::Continue => {}
            // If the recursion should skip, do not apply to its children. And let the recursion continue
            VisitRecursion::Skip => return Ok(VisitRecursion::Continue),
            // If the recursion should stop, do not apply to its children
            VisitRecursion::Stop => return Ok(VisitRecursion::Stop),
        };

        self.visit_subqueries(visitor)?;

        match self.apply_children(&mut |node| node.visit(visitor))? {
            VisitRecursion::Continue => {}
            // If the recursion should skip, do not apply to its children. And let the recursion continue
            VisitRecursion::Skip => return Ok(VisitRecursion::Continue),
            // If the recursion should stop, do not apply to its children
            VisitRecursion::Stop => return Ok(VisitRecursion::Stop),
        }

        visitor.post_visit(self)
    }

    fn map_children<F>(self, transform: F) -> Result<Self>
    where
        F: FnMut(Self) -> Result<Self>,
    {
        let old_children = self.inputs();
        let new_children = old_children
            .iter()
            .map(|&c| c.clone())
            .map(transform)
            .collect::<Result<Vec<_>>>()?;

        // if any changes made, make a new child
        if old_children
            .iter()
            .zip(new_children.iter())
            .any(|(c1, c2)| c1 != &c2)
        {
            self.with_new_exprs(self.expressions(), new_children.as_slice())
        } else {
            Ok(self)
        }
    }
}