Fixed adding optional json

pony/orm/migrations/dbschema.py

@@ -226,6 +226,7 @@ def exists(self, provider, connection, case_sensitive=True):
 
     @classmethod
     def from_attr(cls, table, attr):
+        from pony.orm.ormtypes import Json
         schema = table.schema
         if not attr.converters:
             attr.converters = [schema.provider.get_converter_by_attr(attr)]
@@ -241,8 +242,11 @@ def from_attr(cls, table, attr):
         col.nullable = attr.nullable or len(attr.entity.bases) != 0
         col.auto = attr.auto
         col.sql_default = attr.sql_default
-        if not attr.is_required and isinstance(attr.py_type, type) and issubclass(attr.py_type, basestring):
-            col.sql_default = ''
+        if not attr.is_required and isinstance(attr.py_type, type):
+            if issubclass(attr.py_type, basestring):
+                col.sql_default = ''
+            elif issubclass(attr.py_type, Json):
+                col.sql_default = '{}'
         col.initial = attr.initial or attr.provided.initial
         col.sql_type = attr.sql_type or converter.get_sql_type()
         provided_cols = attr.provided.kwargs.get('columns', None)

pony/orm/migrations/tests/test_schema_ops.py

@@ -1312,6 +1312,50 @@ class NewStudent(Student):
         self.assertEqual(len(migration.operations), 1)  # ChangeDiscriminator
         self.assertEqual(expected_schema, actual_schema)
 
+    def test_add_optional_json(self):
+        self.db2 = db2 = Database(**self.db_params)
+
+        class Department(db2.Entity):
+            number = PrimaryKey(int, auto=True)
+            name = Required(str, unique=True)
+            groups = Set("Group")
+            courses = Set("Course")
+
+        class Group(db2.Entity):
+            number = PrimaryKey(int)
+            major = Required(str, index=True)
+            dept = Required("Department", fk_name='dept_fk')
+            students = Set("Student")
+
+        class Course(db2.Entity):
+            name = Required(str, unique=True)
+            semester = Required(int)
+            lect_hours = Required(int, check='lect_hours > 0')
+            lab_hours = Required(int)
+            credits = Required(int, index=True)
+            dept = Required(Department)
+            students = Set("Student")
+            PrimaryKey(name, semester)
+            composite_index(lect_hours, lab_hours)
+
+        class Student(db2.Entity):
+            name = Required(str)
+            dob = Required(date)
+            tel = Optional(str)
+            picture = Optional(buffer, lazy=True)
+            gpa = Required(float, default=0)
+            group = Required(Group)
+            courses = Set(Course)
+            composite_key(name, dob)
+            complex_info = Optional(Json)
+
+        class NewStudent(Student):
+            avatar = Required(str)
+
+        expected_schema, actual_schema, migration = self.apply_migrate()
+        self.assertEqual(len(migration.operations), 1)  # ChangeDiscriminator
+        self.assertEqual(expected_schema, actual_schema)
+
 
 class TestPostgresMigrations(AbstractTestMigrations):
     db_params = dict(provider='postgres', user='pony', password='pony', host='localhost', database='pony')