feat: {add|alter|drop}_columns APIs (#1015)

Initial work for #959. This exposes the basic functionality for each in
all of the APIs. Will add user guide documentation in a later PR.

python/lancedb/remote/table.py

@@ -15,7 +15,7 @@ import logging
 import uuid
 from concurrent.futures import Future
 from functools import cached_property
-from typing import Dict, Optional, Union
+from typing import Dict, Iterable, Optional, Union
 
 import pyarrow as pa
 from lance import json_to_schema
@@ -473,6 +473,21 @@ class RemoteTable(Table):
             "count_rows() is not yet supported on the LanceDB cloud"
         )
 
+    def add_columns(self, transforms: Dict[str, str]):
+        raise NotImplementedError(
+            "add_columns() is not yet supported on the LanceDB cloud"
+        )
+
+    def alter_columns(self, alterations: Iterable[Dict[str, str]]):
+        raise NotImplementedError(
+            "alter_columns() is not yet supported on the LanceDB cloud"
+        )
+
+    def drop_columns(self, columns: Iterable[str]):
+        raise NotImplementedError(
+            "drop_columns() is not yet supported on the LanceDB cloud"
+        )
+
 
 def add_index(tbl: pa.Table, i: int) -> pa.Table:
     return tbl.add_column(

python/lancedb/table.py

@@ -660,6 +660,56 @@ class Table(ABC):
         For most cases, the default should be fine.
         """
 
+    @abstractmethod
+    def add_columns(self, transforms: Dict[str, str]):
+        """
+        Add new columns with defined values.
+
+        This is not yet available in LanceDB Cloud.
+
+        Parameters
+        ----------
+        transforms: Dict[str, str]
+            A map of column name to a SQL expression to use to calculate the
+            value of the new column. These expressions will be evaluated for
+            each row in the table, and can reference existing columns.
+        """
+
+    @abstractmethod
+    def alter_columns(self, alterations: Iterable[Dict[str, str]]):
+        """
+        Alter column names and nullability.
+
+        This is not yet available in LanceDB Cloud.
+
+        alterations : Iterable[Dict[str, Any]]
+            A sequence of dictionaries, each with the following keys:
+            - "path": str
+                The column path to alter. For a top-level column, this is the name.
+                For a nested column, this is the dot-separated path, e.g. "a.b.c".
+            - "name": str, optional
+                The new name of the column. If not specified, the column name is
+                not changed.
+            - "nullable": bool, optional
+                Whether the column should be nullable. If not specified, the column
+                nullability is not changed. Only non-nullable columns can be changed
+                to nullable. Currently, you cannot change a nullable column to
+                non-nullable.
+        """
+
+    @abstractmethod
+    def drop_columns(self, columns: Iterable[str]):
+        """
+        Drop columns from the table.
+
+        This is not yet available in LanceDB Cloud.
+
+        Parameters
+        ----------
+        columns : Iterable[str]
+            The names of the columns to drop.
+        """
+
 
 class _LanceDatasetRef(ABC):
     @property
@@ -1536,6 +1586,22 @@ class LanceTable(Table):
         """
         return self.to_lance().optimize.compact_files(*args, **kwargs)
 
+    def add_columns(self, transforms: Dict[str, str]):
+        self._dataset_mut.add_columns(transforms)
+
+    def alter_columns(self, *alterations: Iterable[Dict[str, str]]):
+        modified = []
+        # I called this name in pylance, but I think I regret that now. So we
+        # allow both name and rename.
+        for alter in alterations:
+            if "rename" in alter:
+                alter["name"] = alter.pop("rename")
+            modified.append(alter)
+        self._dataset_mut.alter_columns(*modified)
+
+    def drop_columns(self, columns: Iterable[str]):
+        self._dataset_mut.drop_columns(columns)
+
 
 def _sanitize_schema(
     data: pa.Table,

python/pyproject.toml

@@ -62,7 +62,7 @@ lancedb = "lancedb.cli.cli:cli"
 requires = ["setuptools", "wheel"]
 build-backend = "setuptools.build_meta"
 
-[tool.ruff]
+[tool.ruff.lint]
 select = ["F", "E", "W", "I", "G", "TCH", "PERF"]
 
 [tool.pytest.ini_options]

python/tests/test_table.py

@@ -898,3 +898,29 @@ def test_restore_consistency(tmp_path):
     table.add([{"id": 2}])
     assert table_fixed.version == table.version - 1
     assert table_ref_latest.version == table.version
+
+
+# Schema evolution
+def test_add_columns(tmp_path):
+    db = lancedb.connect(tmp_path)
+    data = pa.table({"id": [0, 1]})
+    table = LanceTable.create(db, "my_table", data=data)
+    table.add_columns({"new_col": "id + 2"})
+    assert table.to_arrow().column_names == ["id", "new_col"]
+    assert table.to_arrow()["new_col"].to_pylist() == [2, 3]
+
+
+def test_alter_columns(tmp_path):
+    db = lancedb.connect(tmp_path)
+    data = pa.table({"id": [0, 1]})
+    table = LanceTable.create(db, "my_table", data=data)
+    table.alter_columns({"path": "id", "rename": "new_id"})
+    assert table.to_arrow().column_names == ["new_id"]
+
+
+def test_drop_columns(tmp_path):
+    db = lancedb.connect(tmp_path)
+    data = pa.table({"id": [0, 1], "category": ["a", "b"]})
+    table = LanceTable.create(db, "my_table", data=data)
+    table.drop_columns(["category"])
+    assert table.to_arrow().column_names == ["id"]