I would like to do some handler for exception. I'm using a combination of Flask-restless and SQLAlchemy in python. 

My problem:

When I send request to api with object that already exists in DB, SQLAlchemy shows exception:

```
IntegrityError: (IntegrityError) column <column_name> is not unique u'INSERT INTO ...

```

So I have tried to add attribute `validation_exceptions` into `create_api` method:

```
manager.create_api( ... , validation_exceptions=[IntegrityError])

```

But response json contains:

```
{
    "validation_errors": "Could not determine specific validation errors"
} 

```

and server api shows exception :

```
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\flask_restless\views.py", line 797, in _extract_error_messages
    left, right = str(exception).rsplit(':', 1)
ValueError: need more than 1 value to unpack

```

Exception validation in Flask-restless doesn't work with this type of exception (IntegrityError)

What should I do? Is it possible to create some handler for exception and to return my own error message in json?