如何调用限制为 1 的 SQLAlchemy 查询？

Question

I have code like this:

thing = thing.query.filter_by(id=thing_id).limit(1).all()[0]

all()[0] feels a bit messy and redundant in the limit(1) case. Is there a more terse (and/or otherwise optimal) way to achieve this?

Answer 1

There's first() :

first() applies a limit of one and returns the first result as a scalar

Thus:

thing = thing.query.filter_by(id=thing_id).first()

Answer 2

Jwodder's answer will, indeed, return the first result as a scalar, but SQLAlchemy provides a couple other functions that may better suit your needs, so I have listed and explained all of them:

first() will pull the first row returned, or None if no row is returned.

one() will pull 1 row, but it MUST only pull one row: it will error out if the number of returned rows from your query is not 1.

one_or_none() will essentially do a one() , but instead of erroring out will return None if no rows are returned. This will still error out if more than one rows is returned.

The documentation for all of these can be found here: http://docs.sqlalchemy.org/en/latest/orm/query.html

Answer 3

First of all, agree and support other answers.

However, it looks like that your queries are for the primary key column. If this is the case, the most straightforward way of making such a query would be to simply call get() :

thing = Thing.query.get(thing_id)

Answer 4

SQLAlchemy 核心为查询提供了一个.limit(1) 运算符。