Add MergeStrategy enum and integrate into TargetOptions for enhanced merge configurations

Author: flarco

sling/sling/__init__.py

@@ -4,7 +4,7 @@
 from json import JSONEncoder
 from .hooks import HookMap, Hook, hooks_to_dict
 from .options import SourceOptions, TargetOptions
-from .enum import Mode, Format, Compression
+from .enum import Mode, Format, Compression, MergeStrategy
 from .bin import SLING_BIN
 
 # Try to import pyarrow, fallback to CSV if not available
@@ -46,6 +46,8 @@ def default(self, o):
       return o.value
     elif isinstance(o, Compression):
       return o.value
+    elif isinstance(o, MergeStrategy):
+      return o.value
     elif isinstance(o, datetime.datetime):
       return str(o)
     elif isinstance(o, datetime.date):

sling/sling/enum.py

@@ -47,7 +47,7 @@ class Format(Enum):
 class Compression(Enum):
   """
   Enum representing the available Sling compression types.
-  
+
   AUTO: Auto-detect compression type
   NONE: No compression
   ZIP: ZIP compression
@@ -60,4 +60,19 @@ class Compression(Enum):
   ZIP = "zip"
   GZIP = "gzip"
   SNAPPY = "snappy"
-  ZSTD = "zstd" 
+  ZSTD = "zstd"
+
+
+class MergeStrategy(Enum):
+  """
+  Enum representing the available Sling merge strategies for incremental/backfill modes.
+
+  UPDATE_INSERT: Update existing rows, insert new rows (standard upsert behavior)
+  DELETE_INSERT: Delete matching rows, then insert all (safe and reliable)
+  INSERT: Insert only, skip existing (append-only scenarios)
+  UPDATE: Update only, skip new (update existing records only)
+  """
+  UPDATE_INSERT = "update_insert"
+  DELETE_INSERT = "delete_insert"
+  INSERT = "insert"
+  UPDATE = "update"

sling/sling/options.py

@@ -1,5 +1,5 @@
 from typing import Union
-from .enum import Format, Compression
+from .enum import Format, Compression, MergeStrategy
 
 class SourceOptions:
   trim_space: bool
@@ -81,6 +81,7 @@ class TargetOptions:
   use_bulk: bool
   ignore_existing: bool
   delete_missing: bool
+  merge_strategy: Union[MergeStrategy, str]
   column_casing: str
   column_typing: dict
   add_new_columns: bool
@@ -105,6 +106,7 @@ def __init__(self,
               use_bulk: bool = None,
               ignore_existing: bool = None,
               delete_missing: bool = None,
+              merge_strategy: Union[MergeStrategy, str] = None,
               column_casing: str = None,
               column_typing: dict = None,
               add_new_columns: bool = None,
@@ -128,6 +130,7 @@ def __init__(self,
     self.use_bulk = use_bulk
     self.ignore_existing = ignore_existing
     self.delete_missing = delete_missing
+    self.merge_strategy = merge_strategy
     self.column_casing = column_casing
     self.column_typing = column_typing
     self.add_new_columns = add_new_columns