feat: support ORDER BY in the datafusion planner

rust/lance-graph/src/datafusion_planner.rs

@@ -337,9 +337,30 @@ impl DataFusionPlanner {
                     .build()
                     .unwrap())
             }
-            LogicalOperator::Sort { input, .. } => {
-                // Schema-less placeholder: skip sort for now
-                self.build_operator(ctx, input)
+            LogicalOperator::Sort { input, sort_items } => {
+                use datafusion::logical_expr::SortExpr;
+
+                let input_plan = self.build_operator(ctx, input)?;
+
+                // Convert sort items to DataFusion sort expressions
+                let sort_exprs: Vec<SortExpr> = sort_items
+                    .iter()
+                    .map(|item| {
+                        let expr = self.to_df_value_expr(&item.expression);
+                        let asc = matches!(item.direction, crate::ast::SortDirection::Ascending);
+                        SortExpr {
+                            expr,
+                            asc,
+                            nulls_first: true,
+                        }
+                    })
+                    .collect();
+
+                Ok(LogicalPlanBuilder::from(input_plan)
+                    .sort(sort_exprs)
+                    .unwrap()
+                    .build()
+                    .unwrap())
             }
             LogicalOperator::Limit { input, count } => {
                 let input_plan = self.build_operator(ctx, input)?;
@@ -1611,4 +1632,172 @@ mod tests {
         // Third call should fail (no more instances)
         assert!(ctx.next_relationship_instance("KNOWS").is_err());
     }
+
+    #[test]
+    fn test_order_by_single_column_asc() {
+        use crate::ast::{PropertyRef, SortDirection, ValueExpression};
+        use crate::logical_plan::{LogicalOperator, ProjectionItem, SortItem};
+
+        let cfg = crate::config::GraphConfig::builder()
+            .with_node_label("Person", "id")
+            .build()
+            .unwrap();
+        let planner = DataFusionPlanner::with_catalog(cfg, make_catalog());
+
+        // Build: Project -> Sort
+        let scan = LogicalOperator::ScanByLabel {
+            variable: "n".to_string(),
+            label: "Person".to_string(),
+            properties: Default::default(),
+        };
+
+        let project = LogicalOperator::Project {
+            input: Box::new(scan),
+            projections: vec![ProjectionItem {
+                expression: ValueExpression::Property(PropertyRef {
+                    variable: "n".to_string(),
+                    property: "name".to_string(),
+                }),
+                alias: None,
+            }],
+        };
+
+        let sort = LogicalOperator::Sort {
+            input: Box::new(project),
+            sort_items: vec![SortItem {
+                expression: ValueExpression::Property(PropertyRef {
+                    variable: "n".to_string(),
+                    property: "name".to_string(),
+                }),
+                direction: SortDirection::Ascending,
+            }],
+        };
+
+        let df_plan = planner.plan(&sort).unwrap();
+        let s = format!("{:?}", df_plan);
+
+        // Should contain Sort operator
+        println!("Plan: {}", s);
+        assert!(s.contains("Sort") || s.contains("sort"));
+        assert!(s.contains("n__name"));
+    }
+
+    #[test]
+    fn test_order_by_multiple_columns() {
+        use crate::ast::{PropertyRef, SortDirection, ValueExpression};
+        use crate::logical_plan::{LogicalOperator, ProjectionItem, SortItem};
+
+        let cfg = crate::config::GraphConfig::builder()
+            .with_node_label("Person", "id")
+            .build()
+            .unwrap();
+        let planner = DataFusionPlanner::with_catalog(cfg, make_catalog());
+
+        let scan = LogicalOperator::ScanByLabel {
+            variable: "n".to_string(),
+            label: "Person".to_string(),
+            properties: Default::default(),
+        };
+
+        let project = LogicalOperator::Project {
+            input: Box::new(scan),
+            projections: vec![
+                ProjectionItem {
+                    expression: ValueExpression::Property(PropertyRef {
+                        variable: "n".to_string(),
+                        property: "name".to_string(),
+                    }),
+                    alias: None,
+                },
+                ProjectionItem {
+                    expression: ValueExpression::Property(PropertyRef {
+                        variable: "n".to_string(),
+                        property: "age".to_string(),
+                    }),
+                    alias: None,
+                },
+            ],
+        };
+
+        let sort = LogicalOperator::Sort {
+            input: Box::new(project),
+            sort_items: vec![
+                SortItem {
+                    expression: ValueExpression::Property(PropertyRef {
+                        variable: "n".to_string(),
+                        property: "age".to_string(),
+                    }),
+                    direction: SortDirection::Descending,
+                },
+                SortItem {
+                    expression: ValueExpression::Property(PropertyRef {
+                        variable: "n".to_string(),
+                        property: "name".to_string(),
+                    }),
+                    direction: SortDirection::Ascending,
+                },
+            ],
+        };
+
+        let df_plan = planner.plan(&sort).unwrap();
+        let s = format!("{:?}", df_plan);
+
+        // Should contain Sort with both columns
+        assert!(s.contains("Sort") || s.contains("sort"));
+        assert!(s.contains("n__age"));
+        assert!(s.contains("n__name"));
+    }
+
+    #[test]
+    fn test_order_by_with_limit() {
+        use crate::ast::{PropertyRef, SortDirection, ValueExpression};
+        use crate::logical_plan::{LogicalOperator, ProjectionItem, SortItem};
+
+        let cfg = crate::config::GraphConfig::builder()
+            .with_node_label("Person", "id")
+            .build()
+            .unwrap();
+        let planner = DataFusionPlanner::with_catalog(cfg, make_catalog());
+
+        let scan = LogicalOperator::ScanByLabel {
+            variable: "n".to_string(),
+            label: "Person".to_string(),
+            properties: Default::default(),
+        };
+
+        let project = LogicalOperator::Project {
+            input: Box::new(scan),
+            projections: vec![ProjectionItem {
+                expression: ValueExpression::Property(PropertyRef {
+                    variable: "n".to_string(),
+                    property: "name".to_string(),
+                }),
+                alias: None,
+            }],
+        };
+
+        let sort = LogicalOperator::Sort {
+            input: Box::new(project),
+            sort_items: vec![SortItem {
+                expression: ValueExpression::Property(PropertyRef {
+                    variable: "n".to_string(),
+                    property: "name".to_string(),
+                }),
+                direction: SortDirection::Ascending,
+            }],
+        };
+
+        let limit = LogicalOperator::Limit {
+            input: Box::new(sort),
+            count: 10,
+        };
+
+        let df_plan = planner.plan(&limit).unwrap();
+        let s = format!("{:?}", df_plan);
+
+        // Should contain both Limit and Sort
+        assert!(s.contains("Limit") || s.contains("limit"));
+        assert!(s.contains("Sort") || s.contains("sort"));
+        assert!(s.contains("n__name"));
+    }
 }