Merge pull request #12645 from CredoReference/more-than-one-lti-consumer-with-empty-instance-guid

Ability to create two or more LTI consumers through the Django admin with an empty instance_guid field

openedx/core/djangolib/fields.py

@@ -0,0 +1,28 @@
+"""
+Custom Django fields.
+"""
+from django.db import models
+
+
+class CharNullField(models.CharField):
+    """CharField that stores NULL but returns ''"""
+
+    description = "CharField that stores NULL but returns ''"
+
+    def to_python(self, value):
+        """Converts the value into the correct Python object."""
+        if isinstance(value, models.CharField):
+            return value
+        if value is None:
+            return ""
+        else:
+            return value
+
+    def get_db_prep_value(self, value, connection, prepared=False):
+        """Converts value to a backend-specific value."""
+        if not prepared:
+            value = self.get_prep_value(value)
+        if value == "":
+            return None
+        else:
+            return value