sxql VS mito

There are also packages (in Python, Ruby, R, etc.) that allow you to query databases without directly writing the SQL. I see that there's a package called SxQL that does this in lisp, but I haven't seen it used in Emacs.

You can build custom queries like this in Mito with sxql.

Are you using a custom metaclass for your classes? I know that Mito's metaclass has some issues around this sort of thing for its col-type, so if you're using a metaclass that's trying to resolve the type too early that could lead to problems.

Mito is an object relational mapper for Common Lisp created by Eitaro Fukamachi. It supports MySQL, PostgreSQL and SQLite3. It automatically adds id (serial/uuid primary key), created_at and updated_at by default like Ruby's ActiveRecord. It also provides support for Migrations and DB schema versioning.

Using Mito, one can define a class that corresponds to a table in a database. Instances of this class then correspond to rows in the database, allowing you to work with data in the database through a CLOS interface. (This is pretty standard ORM stuff.)