How to create computed columns ?

First Check

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• I already checked if it is not related to SQLModel but to SQLAlchemy.

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Example Code

class Album(SQLModel):
    title: str
    slug: str
    description: str


# what i've tried but doesn't work e.g : 

#     slug: str = column_property(slugify(title))
# E   NameError: name 'title' is not defined

class Album(SQLModel):
    title: str
    slug: str = column_property(slugify(title))
    description: str

Description

I’m trying to generate a column named “slug” that is a slugified version of “title” so it should be persisted in database, and be updated when title changes.

But so far no luck, I’ve looked at column property but didn’t manage to make it work with SQLModel. I saw that there are events “before update” … but I don’t think this is the way to go

Operating System

Windows

Operating System Details

No response

SQLModel Version

0.0.4

Python Version

3.9.2

Additional Context

No response

[dandiep]

Any other thoughts on how to actually use the computed_property() from SQL alchemy? E.g.

class Parent(SQLModel):
....
    child_count: Optional[int] = Field(sa_column=column_property(
        select(func.count(Child.id)).where(Child.parent_id == id)
    ))

This results in in “column Parent.child_count does not exist.”

[angel-langdon]

Related to this issue https://github.com/tiangolo/sqlmodel/issues/240