Method get_parameter_fields

datafusion/expr/src/logical_plan/plan.rs:1622–1654

Walk the logical plan, find any `Placeholder` tokens, and return a map of their IDs and FieldRefs

(
        &self,
    )

    /// Walk the logical plan, find any `Placeholder` tokens, and return a map of their IDs and FieldRefs
    pub fn get_parameter_fields(
        &self,
    ) -> Result<HashMap<String, Option<FieldRef>>, DataFusionError> {
        let mut param_types: HashMap<String, Option<FieldRef>> = HashMap::new();

        self.apply_with_subqueries(|plan| {
            plan.apply_expressions(|expr| {
                expr.apply(|expr| {
                    if let Expr::Placeholder(Placeholder { id, field }) = expr {
                        let prev = param_types.get(id);
                        match (prev, field) {
                            (Some(Some(prev)), Some(field)) => {
                                check_metadata_with_storage_equal(
                                    (field.data_type(), Some(field.metadata())),
                                    (prev.data_type(), Some(prev.metadata())),
                                    "parameter",
                                    &format!(": Conflicting types for id {id}"),
                                )?;
                            }
                            (_, Some(field)) => {
                                param_types.insert(id.clone(), Some(Arc::clone(field)));
                            }
                            _ => {
                                param_types.insert(id.clone(), None);
                            }
                        }
                    }
                    Ok(TreeNodeRecursion::Continue)
                })
            })
        })
        .map(|_| param_types)
    }

    // ------------
    // Various implementations for printing out LogicalPlans