Set selected wtforms.ext.sqlalchemy.fields.QuerySelectField.

gistfile1.diff

diff --git a/wtforms/ext/sqlalchemy/fields.py b/wtforms/ext/sqlalchemy/fields.py
index 286dada..6c1a40e 100644
--- a/wtforms/ext/sqlalchemy/fields.py
+++ b/wtforms/ext/sqlalchemy/fields.py
@@ -56,9 +56,10 @@ class QuerySelectField(SelectFieldBase):

     def __init__(self, label=None, validators=None, query_factory=None,
                  get_pk=None, get_label=None, allow_blank=False,
-                 blank_text='', **kwargs):
+                 blank_text='', coerce=None, **kwargs):
         super(QuerySelectField, self).__init__(label, validators, **kwargs)
         self.query_factory = query_factory
+        self.coerce = coerce

         if get_pk is None:
             if not has_identity_key:
@@ -105,7 +106,8 @@ class QuerySelectField(SelectFieldBase):
             yield ('__None', self.blank_text, self.data is None)

         for pk, obj in self._get_object_list():
-            yield (pk, self.get_label(obj), obj == self.data)
+            yield (pk, self.get_label(obj), obj == self.data or
+                   (self.coerce is not None and self.coerce(pk) == self.data))

     def process_formdata(self, valuelist):
         if valuelist:
@@ -138,7 +140,7 @@ class QuerySelectMultipleField(QuerySelectField):
     """
     widget = widgets.Select(multiple=True)

-    def __init__(self, label=None, validators=None, default=None, **kwargs):
+    def __init__(self, label=None, validators=None, default=None, coerce=None, **kwargs):
         if default is None:
             default = []
         super(QuerySelectMultipleField, self).__init__(label, validators, default=default, **kwargs)
@@ -146,6 +148,7 @@ class QuerySelectMultipleField(QuerySelectField):
             import warnings
             warnings.warn('allow_blank=True does not do anything for QuerySelectMultipleField.')
         self._invalid_formdata = False
+        self.coerce = None

     def _get_data(self):
         formdata = self._formdata
@@ -170,7 +173,8 @@ class QuerySelectMultipleField(QuerySelectField):

     def iter_choices(self):
         for pk, obj in self._get_object_list():
-            yield (pk, self.get_label(obj), obj in self.data)
+            yield (pk, self.get_label(obj), obj in self.data or
+                   (self.coerce is not None and self.coerce(pk) in self.data))

     def process_formdata(self, valuelist):
         self._formdata = set(valuelist)

Why are you not created PR to WTForms-Alchemy as you advised pallets-eco/wtforms#202?