Posts tagged: sqlalchemy

💭 Creating One-To-Many Relationships in Flask-SQLAlchemy - YouTube

2024-03-06T14:35:17Z

Great example from Anthony showing how easy it is to practice building database orm models and playing with them in a repl. This is good practice even if you are in a big code base to be able to test and learn in a simplified code base that does not have a mountain of other code around atuh, permissions, security, and other complex things that come into real production code bases that might make it hard to focus on what you are trying to do.

Note

Anthony uses backref here, thats legacy, use back_populates on both parent and child.

Note

This post is a thought. It’s a short note that I make about someone else’s content online #thoughts

💭 python - Concepts of backref and back_populate in SQLalchemy? ...

2024-03-06T01:55:42Z

External Link

stackoverflow.com

Today I came across some sqlalchemy models that created some relationships, some used backref some used back_populates. I was stumped why, I had never came accross backref before and I felt skill issues sinking in.

backref is considered legacy #

https://docs.sqlalchemy.org/en/14/orm/backref.html

As stated in the sqlalchemy docs, backref is a legacy feature. Its shorthand to creating relationships between parent and child, but only adding it to the parent. While this is simpler it introduces some invisible magic.

Note

This post is a thought. It’s a short note that I make about someone else’s content online #thoughts

💭 Read a Range of Data - LIMIT and OFFSET - SQLModel

2024-01-12T02:18:35Z

Read a Range of Data - LIMIT and OFFSET - SQLModel

SQLModel, SQL databases in Python, designed for simplicity, compatibility, and robustness.

sqlmodel.tiangolo.com

Today I was running some sqlmodel queries through the sqlalchemy orm. Admittedly I’ve not done enough orm queries before, and I’ve done quite a bit of raw sql. I was trying to get objects from two separate models that had relationships setup.

session.query(User, Images).where(User.id == 3).all()

It is incredibly slow, and gives me the following warning.

SELECT statement has a cartesian product between FROM element(s)

What I learned from the SQLModel docs is that you should give it a join to correct this and go much faster.

session.query(User, Images).join(Images).where(User.id == 3).all()

Note

This post is a thought. It’s a short note that I make about someone else’s content online #thoughts

💭 python - SQLAlchemy ORDER BY DESCENDING? - Stack Overflow

2023-07-29T22:30:25Z

External Link

stackoverflow.com

How to sort results from a sqlalchemy based orm.

.order_by(model.Entry.amount.desc())

I needed this to enable paging on my thoughts api.

@post_router.get("/posts/")
async def get_posts(
    *,
    request: Request,
    session: Session = Depends(get_session),
    hx_request: Annotated[str | None, Header()] = None,
    accept: Annotated[str | None, Header()] = None,
    current_user: Annotated[User, Depends(try_get_current_active_user)],
    page_size: int = 10,
    page: int = 1,
) -> Posts:
    "get all posts"
    statement = (
        select(Post)
        .where(Post.published)
        .order_by(Post.id.desc())
        .limit(page_size)
        .offset((page - 1) * page_size)
    )
    posts = session.exec(statement).all()
    posts = Posts(__root__=posts)

    if isinstance(current_user, RedirectResponse):
        is_logged_in = False
    else:
        is_logged_in = True

    if hx_request and page == 1 and len(posts.__root__) == 0:
        return HTMLResponse('<ul id="posts"><li>No posts</li></ul>')
    if hx_request and len(posts.__root__) == 0:
        return HTMLResponse("")
    if not hx_request and len(posts.__root__) == 0:
        return ["no posts"]
    if hx_request:
        return templates.TemplateResponse(
            "posts.html",
            {
                "request": request,
                "config": config,
                "posts": posts,
                "md": md,
                "is_logged_in": is_logged_in,
                "page": page,
            },
        )

    if accept.startswith("text/html"):
        return templates.TemplateResponse(
            "base.html",
            {
                "request": request,
                "config": config,
                "posts": posts,
                "md": md,
                "is_logged_in": is_logged_in,
                "page": page,
            },
        )

    return posts

Note

This post is a thought. It’s a short note that I make about someone else’s content online #thoughts

💭 Column INSERT/UPDATE Defaults — SQLAlchemy 1.4 Documentation

2023-07-28T14:59:37Z

Column INSERT/UPDATE Defaults — SQLAlchemy 1.4 Documentation

docs.sqlalchemy.org

sqlalchemy server_defaults end up as defaults in the database when new values are inserted.

t = Table(
    "test",
    metadata_obj,
    Column("abc", String(20), server_default="abc"),
    Column("created_at", DateTime, server_default=func.sysdate()),
    Column("index_value", Integer, server_default=text("0")),
)

CREATE TABLE test (
    abc varchar(20) default 'abc',
    created_at datetime default sysdate,
    index_value integer default 0
)

Note

This post is a thought. It’s a short note that I make about someone else’s content online #thoughts