Add error handler for duplicate domain

app/email_branding/rest.py

@@ -1,4 +1,5 @@
-from flask import Blueprint, jsonify, request
+from flask import Blueprint, current_app, jsonify, request
+from sqlalchemy.exc import IntegrityError
 
 from app.dao.email_branding_dao import (
     dao_create_email_branding,
@@ -18,6 +19,22 @@ email_branding_blueprint = Blueprint('email_branding', __name__)
 register_errors(email_branding_blueprint)
 
 
+@email_branding_blueprint.errorhandler(IntegrityError)
+def handle_integrity_error(exc):
+    """
+    Handle integrity errors caused by the unique constraint on domain
+    """
+    if 'domain' in str(exc):
+        return jsonify(
+            result='error',
+            message={'name': ["Duplicate domain '{}'".format(
+                exc.params.get('domain')
+            )]}
+        ), 400
+    current_app.logger.exception(exc)
+    return jsonify(result='error', message="Internal server error"), 500
+
+
 @email_branding_blueprint.route('', methods=['GET'])
 def get_email_branding_options():
     email_branding_options = [o.serialize() for o in dao_get_email_branding_options()]