Thanks for quick response.
After redefining MPC->DEFINE method, getting error.
My code: Inside ZCL_ZGW_GC_01_MPC_EXT->DEFINE
METHOD define.
super->define( ). "Calling Super class Define Method
DATA:
lo_entity TYPE REF TO /iwbep/if_mgw_odata_entity_typ,
lo_property TYPE REF TO /iwbep/if_mgw_odata_property.
lo_entity = model->get_entity_type( iv_entity_name = 'GCUpload' ).
IF lo_entity IS BOUND.
lo_property = lo_entity->get_property( iv_property_name = 'Mimetype' ).
lo_property->set_as_content_type( ).
ENDIF.
ENDMETHOD.