[Sqlalchemy-tickets] Issue #3459: Add .cast shortcut method (zzzeek/sqlalchemy)

[Sebastian B. <iss...@bi...>]

New issue 3459: Add .cast shortcut method
https://bitbucket.org/zzzeek/sqlalchemy/issue/3459/add-cast-shortcut-method

Sebastian Bank:

I often find myself expecting columns/expressions/orm attributes to have a `.cast(type_)` shortcut method (just as they provide `.label`, `.desc`, `.op`, etc.), such that one could write `SELECT CAST(eggs AS text) FROM SPAM` as

```
from sqlalchemy import select, Text

eggs_as_text = select([spam.c.eggs.cast(Text)])
```

(cf. postgres `SELECT eggs::text FROM spam`) instead of

```
from sqlalchemy import select, cast, Text

eggs_as_text = select([cast(spam.c.eggs, Text)])
```

With the recent addition of a [cast method](http://docs.sqlalchemy.org/en/rel_1_0/dialects/postgresql.html#sqlalchemy.dialects.postgresql.JSONElement.cast) on `postgresql.JSONElement`, this might be a good occasion to add it (API consistency).

In a quick test, this wasn't more than two lines in `sqlalchemy.sql.elements.ColumnElement`, but maybe I forgot some edge cases.