alamb commented on code in PR #14544: URL: https://github.com/apache/datafusion/pull/14544#discussion_r1947793559
########## docs/source/library-user-guide/query-optimizer.md: ########## @@ -187,94 +235,101 @@ name to be used in a schema, `display_name` should be used. ### Utilities -There are a number of utility methods provided that take care of some common tasks. +There are a number of [utility methods][util] provided that take care of some common tasks. -### ExprVisitor +[util]: https://github.com/apache/datafusion/blob/main/datafusion/expr/src/utils.rs -The `ExprVisitor` and `ExprVisitable` traits provide a mechanism for applying a visitor pattern to an expression tree. +### Recursively walk an expression tree -Here is an example that demonstrates this. +The [TreeNode API] provides a convenient way to recursively walk an expression or plan tree. -```rust -fn extract_subquery_filters(expression: &Expr, extracted: &mut Vec<Expr>) -> Result<()> { - struct InSubqueryVisitor<'a> { - accum: &'a mut Vec<Expr>, - } +For example, to find all subquery references in a logical plan, the following code can be used: - impl ExpressionVisitor for InSubqueryVisitor<'_> { - fn pre_visit(self, expr: &Expr) -> Result<Recursion<Self>> { +```rust +# use datafusion::prelude::*; +# use datafusion::common::tree_node::{TreeNode, TreeNodeRecursion}; +# use datafusion::common::Result; +// Return all subquery references in an expression +fn extract_subquery_filters(expression: &Expr) -> Result<Vec<&Expr>> { + let mut extracted = vec![]; + expression.apply(|expr| { if let Expr::InSubquery(_) = expr { - self.accum.push(expr.to_owned()); + extracted.push(expr); } - Ok(Recursion::Continue(self)) - } - } + Ok(TreeNodeRecursion::Continue) + })?; + Ok(extracted) +} +``` + +Likewise you can use the [TreeNode API] to rewrite a `LogicalPlan` or `ExecutionPlan` Review Comment: I rewrote these examples using the TreeNode API -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For additional commands, e-mail: github-h...@datafusion.apache.org
