Custom model ORM validation

Is there any way to make custom validation on ORM object before save entity?

example:
```

auto dbClientPtr = drogon::app().getDbClient();
Mapper mp(dbClientPtr);

Json::Value json;
json["username"] = username;
json["email"] = email;

drogon_model::PROJECTNAME::Users user(json);

mp.insert(user);
```

model is auto generated by drogon_ctl, so we cant edit the model. What we can do to not include validation code in controller every time when we save entity by mp.insert, mp.update etc

if i wrap code with try catch i will se DB errors from DrogonDbException.

Is there way to make custom Exception, so custom Validation to run custom Exception?