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SQLAlchemy ORDER BY FIELD()

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');

for the output:

letter
------
  g
  a
  c
  k

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')))

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.

like image 546
Adam Morris Avatar asked Sep 16 '11 10:09

Adam Morris


2 Answers

A sqlalchemy func expression can be used to generate the order by field clause:

session.query(AlphabetTable) \
    .filter(AlphabetTable.letter.in_("gack")) \
    .order_by(sqlalchemy.func.field(AlphabetTable.letter, *"gack"))
like image 121
Tim Van Steenburgh Avatar answered Oct 18 '22 23:10

Tim Van Steenburgh


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))))
like image 11
SingleNegationElimination Avatar answered Oct 18 '22 23:10

SingleNegationElimination