[Sqlalchemy-tickets] Issue #2993: db.Model without primary key generates a confusing error message (zzzeek/sqlalchemy)

[Ling T. <iss...@bi...>]

New issue 2993: db.Model without primary key generates a confusing error message
https://bitbucket.org/zzzeek/sqlalchemy/issue/2993/dbmodel-without-primary-key-generates-a

Ling Thio:

When a model definition does not contain a primary key, the following error message appears:

sqlalchemy.exc.InvalidRequestError: Class <class 'XYZ'> does not have a __table__ or __tablename__ specified and does not inherit from an existing table-mapped class.

Example:

```
#!python

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
db = SQLAlchemy(app)

class Xyz(db.Model):
    name = db.Column(db.String(50))
```

It would be nice if the error message:
a) specifically mentions the missing primary key, or
b) prints the current error message, with the addition of the possibility of a missing primary key.