diff --git a/graphene/contrib/sqlalchemy/options.py b/graphene/contrib/sqlalchemy/options.py
index 3040dc3c..44886287 100644
--- a/graphene/contrib/sqlalchemy/options.py
+++ b/graphene/contrib/sqlalchemy/options.py
@@ -2,7 +2,7 @@ from ...core.classtypes.objecttype import ObjectTypeOptions
 from ...relay.types import Node
 from ...relay.utils import is_node
 
-VALID_ATTRS = ('model', 'only_fields', 'exclude_fields')
+VALID_ATTRS = ('model', 'only_fields', 'exclude_fields', 'identifier')
 
 
 class SQLAlchemyOptions(ObjectTypeOptions):
@@ -10,7 +10,7 @@ class SQLAlchemyOptions(ObjectTypeOptions):
     def __init__(self, *args, **kwargs):
         super(SQLAlchemyOptions, self).__init__(*args, **kwargs)
         self.model = None
-        self.identifier = None
+        self.identifier = "id"
         self.valid_attrs += VALID_ATTRS
         self.only_fields = None
         self.exclude_fields = []
diff --git a/graphene/contrib/sqlalchemy/types.py b/graphene/contrib/sqlalchemy/types.py
index 8af80325..f466a1af 100644
--- a/graphene/contrib/sqlalchemy/types.py
+++ b/graphene/contrib/sqlalchemy/types.py
@@ -109,11 +109,15 @@ class SQLAlchemyNode(six.with_metaclass(
     class Meta:
         abstract = True
 
+    def to_global_id(self):
+        id_ = getattr(self.instance, self._meta.identifier)
+        return self.global_id(id_)
+
     @classmethod
     def get_node(cls, id, info=None):
         try:
             model = cls._meta.model
-            identifier = cls._meta.identifier or "id"
+            identifier = cls._meta.identifier
             query = get_query(model, info)
             instance = query.filter(getattr(model, identifier) == id).one()
             return cls(instance)