SQLAlchemy ORDER BY FIELD() [英] SQLAlchemy ORDER BY FIELD()

问题描述

我正在尝试按字段对 SQLAlchemy ORM 对象进行排序，但具有特定的值顺序(既不是升序也不是降序).如果我在 MySQL 上做这个查询，它看起来像;

I am trying to sort an SQLAlchemy ORM object by a field, but with a specific order of the values (which is neither ascending or descending). If I was doing this query on MySQL, it would look like;

SELECT letter FROM alphabet_table WHERE letter in ('g','a','c','k')
ORDER BY FIELDS( letter, 'g','a','c','k');

对于输出:

letter
------
  g
  a
  c
  k

对于 SQLAlchemy，我一直在尝试以下方法:

For SQLAlchemy, I've been trying things along the lines of:

session.query(AlphabetTable).filter(AlphabetTable.letter.in_(('g','a','c','k'))).order_by(AlphabetTable.letter.in_(('g'),'a','c','k'))))

session.query(AlphabetTable).filter(AlphabetTable.letter.in_(('g','a','c','k'))).order_by(AlphabetTable.letter.in_(('g','a','c','k')))

哪个不起作用...有什么想法吗?这是一个小的一次性常量列表，我可以用订单创建一个表然后加入，但这似乎有点太多了.

Which doesn't work... any ideas? It's a small one-time constant list, and I could just create a table with the order and then join, but that seems like a bit too much.

推荐答案

这可能不是一个非常令人满意的解决方案，但是如何使用 case 表达式 而不是按字段排序:

This may not be a very satisfying solution, but how about using a case expression instead of order by fields:

sqlalchemy.orm.Query(AlphabetTable) \
    .filter(AlphabetTable.letter.in_("gack")) \
    .order_by(sqlalchemy.sql.expression.case(((AlphabetTable.letter == "g", 1),
                                              (AlphabetTable.letter == "a", 2),
                                              (AlphabetTable.letter == "c", 3),
                                              (AlphabetTable.letter == "k", 4))))

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