fix: return Arrow JSON from FileFragment.take

python/python/tests/test_dataset.py

@@ -964,6 +964,49 @@ def test_take_with_projection(tmp_path: Path):
     assert table3 == table2
 
 
+def test_take_with_json_column(tmp_path: Path):
+    """Test that take/take_rows return JSON columns in Arrow JSON format (Utf8).
+
+    Previously, take would return lance.json (LargeBinary) instead of
+    arrow.json (Utf8), which is the user-facing format.
+    """
+    json_type = pa.json_()
+    data = pa.table(
+        {
+            "id": pa.array(range(10), type=pa.int64()),
+            "meta": pa.array(
+                [f'{{"val":{i}}}' for i in range(10)],
+                type=json_type,
+            ),
+        }
+    )
+    base_dir = tmp_path / "test_take_json"
+    lance.write_dataset(data, base_dir)
+    dataset = lance.dataset(base_dir)
+
+    # Dataset.take should return arrow.json type
+    result = dataset.take([2, 5, 8])
+    meta_field = result.schema.field("meta")
+    assert meta_field.type == pa.utf8() or meta_field.type == pa.json_(), (
+        f"Expected arrow.json (Utf8), got {meta_field.type}"
+    )
+    metas = result.column("meta").to_pylist()
+    assert metas[0] == '{"val":2}'
+    assert metas[1] == '{"val":5}'
+    assert metas[2] == '{"val":8}'
+
+    # Dataset._take_rows should also return arrow.json type
+    result = dataset._take_rows([0, 3, 9])
+    meta_field = result.schema.field("meta")
+    assert meta_field.type == pa.utf8() or meta_field.type == pa.json_(), (
+        f"Expected arrow.json (Utf8), got {meta_field.type}"
+    )
+    metas = result.column("meta").to_pylist()
+    assert metas[0] == '{"val":0}'
+    assert metas[1] == '{"val":3}'
+    assert metas[2] == '{"val":9}'
+
+
 def test_filter(tmp_path: Path):
     table = pa.Table.from_pydict({"a": range(100), "b": range(100)})
     base_dir = tmp_path / "test"

python/python/tests/test_fragment.py

@@ -835,3 +835,33 @@ def test_fragment_delete_rows(tmp_path: Path):
         frag.delete_rows([100])
     with pytest.raises(ValueError, match="out of range"):
         frag.delete_rows([0, 50, 1000])
+
+
+def test_fragment_take_with_json_column(tmp_path):
+    """Test that FileFragment.take returns JSON columns in Arrow JSON format."""
+    json_type = pa.json_()
+    data = pa.table(
+        {
+            "id": pa.array(range(10), type=pa.int64()),
+            "meta": pa.array(
+                [f'{{"val":{i}}}' for i in range(10)],
+                type=json_type,
+            ),
+        }
+    )
+    dataset_uri = tmp_path / "test_frag_take_json"
+    dataset = lance.write_dataset(data, dataset_uri)
+
+    fragment = dataset.get_fragment(0)
+    result = fragment.take([1, 4, 7])
+
+    # Should return arrow.json type (Utf8), not lance.json (LargeBinary)
+    meta_field = result.schema.field("meta")
+    assert meta_field.type == pa.utf8() or meta_field.type == pa.json_(), (
+        f"Expected arrow.json (Utf8), got {meta_field.type}"
+    )
+
+    metas = result.column("meta").to_pylist()
+    assert metas[0] == '{"val":1}'
+    assert metas[1] == '{"val":4}'
+    assert metas[2] == '{"val":7}'

rust/lance/src/dataset/fragment.rs

@@ -1572,8 +1572,22 @@ impl FileFragment {
         };
 
         // Then call take rows
-        self.take_rows(&row_ids, projection, false, false, false, false)
-            .await
+        let batch = self
+            .take_rows(&row_ids, projection, false, false, false, false)
+            .await?;
+
+        // Convert Lance JSON columns (LargeBinary/JSONB) back to Arrow JSON (Utf8)
+        // for user-facing output.
+        if batch
+            .schema()
+            .fields()
+            .iter()
+            .any(|f| lance_arrow::json::is_json_field(f) || lance_arrow::json::has_json_fields(f))
+        {
+            Ok(lance_arrow::json::convert_lance_json_to_arrow(&batch)?)
+        } else {
+            Ok(batch)
+        }
     }
 
     /// Get the deletion vector for this fragment, using the cache if available.