[Datastore] Align DataFrameSource key_field column name to other sour…

…ces (#959)

mlrun/datastore/sources.py

@@ -33,7 +33,7 @@ def get_source_step(source, key_fields=None, time_field=None):
     """initialize the source driver"""
     if hasattr(source, "to_csv"):
         source = DataFrameSource(source)
-    if not key_fields and not source.key_fields:
+    if not key_fields and not source.key_field:
         raise mlrun.errors.MLRunInvalidArgumentError("key column is not defined")
     return source.to_step(key_fields, time_field)
 
@@ -183,17 +183,17 @@ def to_step(self, key_field=None, time_field=None):
 class DataFrameSource:
     support_storey = True
 
-    def __init__(self, df, key_fields=None, time_field=None):
+    def __init__(self, df, key_field=None, time_field=None):
         self._df = df
-        self.key_fields = key_fields
+        self.key_field = key_field
         self.time_field = time_field
 
-    def to_step(self, key_fields=None, time_field=None):
+    def to_step(self, key_field=None, time_field=None):
         import storey
 
         return storey.DataframeSource(
             dfs=self._df,
-            key_field=self.key_fields or key_fields,
+            key_field=self.key_field or key_field,
             time_field=self.time_field or time_field,
         )