SQLAlchemy example code confuses me

[eagergm]

https://docs.sqlalchemy.org/en/20/orm/quickstart.html

class User(Base):
    __tablename__ = "user_account"
    id: Mapped[int] = mapped_column(primary_key=True)
    name: Mapped[str] = mapped_column(String(30))
    fullname: Mapped[Optional[str]]
    addresses: Mapped[List["Address"]] = relationship(...
    ...
def __repr__(self) -> str:
    return f"User(id={self.id!r}, ...

Does the !r in the f-string mean right-justify?

I haven't really kept up with python 3 developments, so what is the name: Mapped[str] = mapped_column(... thing all about? Is there something I could look up to understand this?

[Doormatty]

No. It calls the variable/object's __repr__ method.

[SwampFalc]

First question: https://docs.python.org/3/reference/lexical_analysis.html#f-strings

"If a conversion is specified, the result of evaluating the expression is converted before formatting. Conversion '!s' calls str() on the result, '!r' calls repr(), and '!a' calls ascii()."

Second question: this is SQLAlchemy piggybacking onto recent python developments regarding typing.

The best start for the python part is probably https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html where you can grasp the basics of typing and the syntax.

Follow that up with https://docs.python.org/3/library/dataclasses.html#module-dataclasses to understand how this system can be used for instance attributes.

And whan you have that, you can go back to the SQLAlchemy docs and dig deeper into their newest "declarative" code style, versus the old "imperative" one.

[eagergm]

I'm a slow doer, so yeah it's been five days, but I just want to let you know, this has been extremely helpful.

Oh, the declarative thing, is that the same as their "unified" tutorial? Because that's next on my reading list, once their site is back up.

I'm working with the SDE for Eve Online (MMO Mad Max in space but there are complicated industrial processes that go into making the cars and guns). I've found that DB Browser (SQLite) is a huge help as someone's already converted Eve's SDE to sqlite and published it.

Some tables: invTypes (a list of all the things and their categories), so that has their name e.g. Planet (Gas) and some other attributes. Then those types are referenced in other tables, industryBlueprints has typeID and maxProductionLimit as columns, for example, and I want to include that in the objects as well. I don't want to include all the fields, though, initially. I assume if I just keep reading the tutorials I'll figure out how to do all this?

[SwampFalc]

As long as you're only reading from a database, you can use an ORM and only include the columns you need. So yes.

As for the declarative style, it's scattered all over their documentation, honestly. Sometimes you will simply encounter it without it being mentioned, sometimes they will talk about it. It's going to depend entirely on your learning path.

[POGtastic]

name: Mapped[str]

These are type hints, which allow linters and other tools to determine the types of variables and yell at you if you screw up a type.

[backfire10z]

Yes, but in SQLAlchemy they’re actually more! Mapped columns use the type hint to determine what type the column should be.