fix: support dynamic projection on remote table (#3023)

The remote server expects an object (`{"alias": "col"}`) and the client
was previously sending a list of tuples `[["alias", "col"]]`

rust/lancedb/src/remote/table.rs

@@ -423,12 +423,11 @@ impl<S: HttpSend> RemoteTable<S> {
                 );
             }
             Select::Dynamic(pairs) => {
-                body["columns"] = serde_json::Value::Array(
-                    pairs
-                        .iter()
-                        .map(|(name, expr)| serde_json::json!([name, expr]))
-                        .collect(),
-                );
+                let alias_map =
+                    serde_json::Map::from_iter(pairs.iter().map(|(name, expr)| {
+                        (name.clone(), serde_json::Value::String(expr.clone()))
+                    }));
+                body["columns"] = alias_map.into();
             }
         }
 

rust/lancedb/src/table.rs

@@ -3163,6 +3163,7 @@ mod tests {
     use arrow_array::{BinaryArray, LargeBinaryArray};
     use arrow_data::ArrayDataBuilder;
     use arrow_schema::{DataType, Field, Schema};
+    use futures::TryStreamExt;
     use lance::dataset::WriteMode;
     use lance::io::{ObjectStoreParams, WrappingObjectStore};
     use lance::Dataset;
@@ -3174,6 +3175,8 @@ mod tests {
     use crate::connection::ConnectBuilder;
     use crate::index::scalar::{BTreeIndexBuilder, BitmapIndexBuilder};
     use crate::index::vector::{IvfHnswPqIndexBuilder, IvfHnswSqIndexBuilder};
+    use crate::query::{ExecutableQuery, QueryBase};
+    use crate::test_utils::connection::new_test_connection;
 
     #[tokio::test]
     async fn test_open() {
@@ -3604,6 +3607,31 @@ mod tests {
         assert_eq!(table.list_indices().await.unwrap().len(), 0);
     }
 
+    #[tokio::test]
+    async fn test_dynamic_select() {
+        let tc = new_test_connection().await.unwrap();
+        let db = tc.connection;
+
+        let table = db
+            .create_table("test", some_sample_data())
+            .execute()
+            .await
+            .unwrap();
+
+        let query = table.query().select(Select::dynamic(&[("i_alias", "i")]));
+
+        let result = query.execute().await;
+        let batches = result
+            .expect("should have result")
+            .try_collect::<Vec<_>>()
+            .await
+            .unwrap();
+
+        for batch in batches {
+            assert!(batch.column_by_name("i_alias").is_some());
+        }
+    }
+
     #[tokio::test]
     async fn test_ivf_pq_uses_default_partition_size_for_num_partitions() {
         use arrow_array::{Float32Array, RecordBatch};