alamb commented on code in PR #5521:
URL: https://github.com/apache/arrow-datafusion/pull/5521#discussion_r1131407108
##########
datafusion/expr/src/logical_plan/extension.rs:
##########
@@ -17,16 +17,15 @@
//! This module defines the interface for logical nodes
use crate::{Expr, LogicalPlan};
-use datafusion_common::DFSchemaRef;
+use datafusion_common::{DFSchema, DFSchemaRef};
use std::hash::{Hash, Hasher};
use std::{any::Any, cmp::Eq, collections::HashSet, fmt, sync::Arc};
-/// This defines the interface for `LogicalPlan` nodes that can be
+/// This defines the interface for [`LogicalPlan`] nodes that can be
/// used to extend DataFusion with custom relational operators.
///
-/// See the example in
-/// [user_defined_plan.rs](../../tests/user_defined_plan.rs) for an
-/// example of how to use this extension API.
+/// Trait [`UserDefinedLogicalNodeCore`] is *the recommended way to implement*
Review Comment:
👍
##########
datafusion/expr/src/logical_plan/extension.rs:
##########
@@ -178,3 +173,109 @@ impl std::cmp::PartialEq for dyn UserDefinedLogicalNode {
}
impl Eq for dyn UserDefinedLogicalNode {}
+
+/// This trait facilitates implementation of the [`UserDefinedLogicalNode`].
+///
+/// See the example in
+/// [user_defined_plan.rs](../../tests/user_defined_plan.rs) for an
+/// example of how to use this extension API.
+pub trait UserDefinedLogicalNodeCore:
+ fmt::Debug + Eq + Hash + Send + Sync + 'static
+{
+ /// Return the plan's name.
+ fn name(&self) -> &str;
+
+ /// Return the logical plan's inputs.
+ fn inputs(&self) -> Vec<&LogicalPlan>;
+
+ /// Return the output schema of this logical plan node.
+ fn schema(&self) -> &DFSchemaRef;
+
+ /// Returns all expressions in the current logical plan node. This
+ /// should not include expressions of any inputs (aka
+ /// non-recursively). These expressions are used for optimizer
+ /// passes and rewrites.
+ fn expressions(&self) -> Vec<Expr>;
+
+ /// A list of output columns (e.g. the names of columns in
+ /// self.schema()) for which predicates can not be pushed below
+ /// this node without changing the output.
+ ///
+ /// By default, this returns all columns and thus prevents any
+ /// predicates from being pushed below this node.
+ fn prevent_predicate_push_down_columns(&self) -> HashSet<String> {
+ // default (safe) is all columns in the schema.
+ get_all_columns_from_schema(self.schema())
+ }
+
+ /// Write a single line, human readable string to `f` for use in explain
plan.
+ ///
+ /// For example: `TopK: k=10`
+ fn fmt_for_explain(&self, f: &mut fmt::Formatter) -> fmt::Result;
+
+ /// Create a new `ExtensionPlanNode` with the specified children
+ /// and expressions. This function is used during optimization
+ /// when the plan is being rewritten and a new instance of the
+ /// `ExtensionPlanNode` must be created.
+ ///
+ /// Note that exprs and inputs are in the same order as the result
+ /// of self.inputs and self.exprs.
+ ///
+ /// So, `self.from_template(exprs, ..).expressions() == exprs
+ #[allow(clippy::wrong_self_convention)]
+ fn from_template(&self, exprs: &[Expr], inputs: &[LogicalPlan]) -> Self;
+}
+
+impl<T: UserDefinedLogicalNodeCore> UserDefinedLogicalNode for T {
Review Comment:
```suggestion
/// Automatically derive UserDefinedLogicalNode to `UserDefinedLogicalNode`
/// to avoid boiler plate for implementing `as_any`, `Hash` and `PartialEq`
impl<T: UserDefinedLogicalNodeCore> UserDefinedLogicalNode for T {
```
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