diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85063e1..03b8ca4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,26 @@
 # Changelog
 
+## 6.0.0
+
+### Breaking Changes
+
+- **`WriteMode.OVERWRITE_PARTITIONS` is deprecated and now raises an error if used.**
+
+  `WriteMode.OVERWRITE_PARTITIONS` remains in the enum for backward compatibility but will raise a `ValueError` at runtime.
+
+  **Migration:** Use `WriteMode.OVERWRITE` to replace all records, or `WriteMode.MERGE` for targeted updates by primary key:
+
+  ```python
+  # Before
+  client.write_to_dlo("MyTable__dll", df, write_mode=WriteMode.OVERWRITE_PARTITIONS)
+
+  # After (full replacement)
+  client.write_to_dlo("MyTable__dll", df, write_mode=WriteMode.OVERWRITE)
+
+  # After (update specific rows by primary key)
+  client.write_to_dlo("MyTable__dll", df, write_mode=WriteMode.MERGE)
+  ```
+
 ## 3.0.0
 
 ### Breaking Changes
diff --git a/src/datacustomcode/io/writer/base.py b/src/datacustomcode/io/writer/base.py
index e4224f7..cb01f76 100644
--- a/src/datacustomcode/io/writer/base.py
+++ b/src/datacustomcode/io/writer/base.py
@@ -27,11 +27,21 @@
 class WriteMode(str, Enum):
     APPEND = "append"
     OVERWRITE = "overwrite"
-    OVERWRITE_PARTITIONS = "overwrite_partitions"
+    OVERWRITE_PARTITIONS = "overwrite_partitions"  # Deprecated: raises error if used
     MERGE = "merge"
     MERGE_UPSERT_DELETE = "merge_upsert_delete"
 
 
+class MergeRecordType(str, Enum):
+    """Values for the _merge_record_type column used by MERGE_UPSERT_DELETE."""
+
+    UPSERT = "UPSERT"
+    DELETE = "DELETE"
+
+
+MERGE_RECORD_TYPE_COLUMN = "_merge_record_type"
+
+
 class BaseDataCloudWriter(BaseDataAccessLayer):
     """Base class for Data Cloud writers."""
 
diff --git a/src/datacustomcode/templates/function/.devcontainer/devcontainer.json b/src/datacustomcode/templates/function/.devcontainer/devcontainer.json
index 3bdca00..38d8d9a 100644
--- a/src/datacustomcode/templates/function/.devcontainer/devcontainer.json
+++ b/src/datacustomcode/templates/function/.devcontainer/devcontainer.json
@@ -5,6 +5,6 @@
 		"dockerfile": "../Dockerfile"
 	},
 	"features": {
-		"ghcr.io/devcontainers/features/git:1": {},
+		"ghcr.io/devcontainers/features/git:1": {}
 	}
 }
diff --git a/src/datacustomcode/templates/script/.devcontainer/devcontainer.json b/src/datacustomcode/templates/script/.devcontainer/devcontainer.json
index 3bdca00..38d8d9a 100644
--- a/src/datacustomcode/templates/script/.devcontainer/devcontainer.json
+++ b/src/datacustomcode/templates/script/.devcontainer/devcontainer.json
@@ -5,6 +5,6 @@
 		"dockerfile": "../Dockerfile"
 	},
 	"features": {
-		"ghcr.io/devcontainers/features/git:1": {},
+		"ghcr.io/devcontainers/features/git:1": {}
 	}
 }
diff --git a/tests/io/writer/test_csv.py b/tests/io/writer/test_csv.py
index 4db45cb..0834298 100644
--- a/tests/io/writer/test_csv.py
+++ b/tests/io/writer/test_csv.py
@@ -37,9 +37,10 @@ def test_write_to_dlo(self, csv_writer, mock_dataframe):
         test_cases = [
             ("test_dlo", WriteMode.OVERWRITE),
             ("another_dlo", WriteMode.APPEND),
-            ("third_dlo", WriteMode.OVERWRITE_PARTITIONS),
-            ("fourth_dlo", WriteMode.MERGE),
+            ("third_dlo", WriteMode.MERGE),
+            ("fourth_dlo", WriteMode.MERGE_UPSERT_DELETE),
         ]
+        # Note: OVERWRITE_PARTITIONS is deprecated and raises an error if used
 
         for name, write_mode in test_cases:
             # Call the method
@@ -58,9 +59,10 @@ def test_write_to_dmo(self, csv_writer, mock_dataframe):
         test_cases = [
             ("test_dmo", WriteMode.OVERWRITE),
             ("another_dmo", WriteMode.APPEND),
-            ("third_dmo", WriteMode.OVERWRITE_PARTITIONS),
+            ("third_dmo", WriteMode.MERGE),
             ("fourth_dmo", WriteMode.MERGE_UPSERT_DELETE),
         ]
+        # Note: OVERWRITE_PARTITIONS is deprecated and raises an error if used
 
         for name, write_mode in test_cases:
             # Call the method