feat: set column metadata from python

Signed-off-by: Martin Andersson <u.martin.andersson@gmail.com>

python/deltalake/_internal.pyi

@@ -225,6 +225,13 @@ class RawDeltaTable:
         allow_out_of_range: bool = False,
     ) -> pyarrow.RecordBatchReader: ...
     def transaction_versions(self) -> Dict[str, Transaction]: ...
+    def set_column_metadata(
+        self,
+        column: str,
+        metadata: dict[str, str],
+        commit_properties: Optional[CommitProperties],
+        post_commithook_properties: Optional[PostCommitHookProperties],
+    ) -> None: ...
     def __datafusion_table_provider__(self) -> Any: ...
 
 def rust_core_version() -> str: ...

python/deltalake/table.py

@@ -2167,6 +2167,28 @@ def set_table_properties(
             commit_properties,
         )
 
+    def set_column_metadata(
+        self,
+        column: str,
+        metadata: dict[str, str],
+        commit_properties: Optional[CommitProperties] = None,
+        post_commithook_properties: Optional[PostCommitHookProperties] = None,
+    ) -> None:
+        """
+        Update a field's metadata in a schema. If the metadata key does not exist, the entry is inserted.
+
+        If the column name doesn't exist in the schema - an error is raised.
+
+        :param column: name of the column to update metadata for.
+        :param metadata: the metadata to be added or modified on the column.
+        :param commit_properties: properties of the transaction commit. If None, default values are used.
+        :param post_commithook_properties: properties for the post commit hook. If None, default values are used.
+        :return:
+        """
+        self.table._table.set_column_metadata(
+            column, metadata, commit_properties, post_commithook_properties
+        )
+
 
 class TableOptimizer:
     """API for various table optimization commands."""

python/src/lib.rs

@@ -18,7 +18,7 @@ use arrow::pyarrow::PyArrowType;
 use chrono::{DateTime, Duration, FixedOffset, Utc};
 use datafusion_ffi::table_provider::FFI_TableProvider;
 use delta_kernel::expressions::Scalar;
-use delta_kernel::schema::StructField;
+use delta_kernel::schema::{MetadataValue, StructField};
 use deltalake::arrow::compute::concat_batches;
 use deltalake::arrow::ffi_stream::{ArrowArrayStreamReader, FFI_ArrowArrayStream};
 use deltalake::arrow::record_batch::{RecordBatch, RecordBatchIterator};
@@ -63,13 +63,6 @@ use error::DeltaError;
 use futures::future::join_all;
 use tracing::log::*;
 
-use pyo3::exceptions::{PyRuntimeError, PyValueError};
-use pyo3::prelude::*;
-use pyo3::pybacked::PyBackedStr;
-use pyo3::types::{PyCapsule, PyDict, PyFrozenSet};
-use serde_json::{Map, Value};
-use uuid::Uuid;
-
 use crate::error::DeltaProtocolError;
 use crate::error::PythonError;
 use crate::features::TableFeatures;
@@ -78,6 +71,14 @@ use crate::merge::PyMergeBuilder;
 use crate::query::PyQueryBuilder;
 use crate::schema::{schema_to_pyobject, Field};
 use crate::utils::rt;
+use deltalake::operations::update_field_metadata::UpdateFieldMetadataBuilder;
+use deltalake::protocol::DeltaOperation::UpdateFieldMetadata;
+use pyo3::exceptions::{PyRuntimeError, PyValueError};
+use pyo3::prelude::*;
+use pyo3::pybacked::PyBackedStr;
+use pyo3::types::{PyCapsule, PyDict, PyFrozenSet};
+use serde_json::{Map, Value};
+use uuid::Uuid;
 
 #[cfg(all(target_family = "unix", not(target_os = "emscripten")))]
 use jemallocator::Jemalloc;
@@ -1521,6 +1522,43 @@ impl RawDeltaTable {
         }
     }
 
+    #[pyo3(signature = (field_name, metadata, commit_properties=None, post_commithook_properties=None))]
+    pub fn set_column_metadata(
+        &self,
+        py: Python,
+        field_name: &str,
+        metadata: HashMap<String, String>,
+        commit_properties: Option<PyCommitProperties>,
+        post_commithook_properties: Option<PyPostCommitHookProperties>,
+    ) -> PyResult<()> {
+        let table = py.allow_threads(|| {
+            let mut cmd = UpdateFieldMetadataBuilder::new(self.log_store()?, self.cloned_state()?);
+
+            cmd = cmd.with_field_name(field_name).with_metadata(
+                metadata
+                    .iter()
+                    .map(|(k, v)| (k.clone(), MetadataValue::String(v.clone())))
+                    .collect(),
+            );
+
+            if let Some(commit_properties) =
+                maybe_create_commit_properties(commit_properties, post_commithook_properties)
+            {
+                cmd = cmd.with_commit_properties(commit_properties)
+            }
+
+            if self.log_store()?.name() == "LakeFSLogStore" {
+                cmd = cmd.with_custom_execute_handler(Arc::new(LakeFSCustomExecuteHandler {}))
+            }
+
+            rt().block_on(cmd.into_future())
+                .map_err(PythonError::from)
+                .map_err(PyErr::from)
+        })?;
+        self.set_state(table.state)?;
+        Ok(())
+    }
+
     fn __datafusion_table_provider__<'py>(
         &self,
         py: Python<'py>,

python/tests/test_alter.py

@@ -457,3 +457,18 @@ def test_add_feautres(existing_sample_table: DeltaTable):
             "v2Checkpoint",
         ]
     )  # type: ignore
+
+
+def test_set_column_metadata(tmp_path: pathlib.Path, sample_table: pa.Table):
+    write_deltalake(tmp_path, sample_table)
+
+    dt = DeltaTable(tmp_path)
+
+    dt.alter.set_column_metadata("price", {"comment": "my comment"})
+
+    fields_by_name = {field.name: field for field in dt.schema().fields}
+    assert fields_by_name["price"].metadata == {"comment": "my comment"}
+
+    with pytest.raises(DeltaError):
+        # Can't set metadata for non existing column.
+        dt.alter.set_column_metadata("non_existing_column", {"comment": "my comment"})