Django : Joining two tables and using extra field from second table for order_by

Question

I have two models A, B

Mysql query is

SELECT a.ID FROM a INNER JOIN b ON ( a.ID = b.id ) WHERE ( b.key = 'vcount' ) AND (a.type = 'abc') AND (a.status = 'done') ORDER BY b.value+0 DESC LIMIT 0, 5

//Here b.value is longtext field, so added 0 to convert to Integer, then sorted.

I need Django query for the same.

I have tried this

A.objects.filter(b__key ="vcount",type = "abc",status = "done").order_by('-b__value')[:5]  

but above Django query is giving wrong result, since it is sorting by Ascii value

So need to convert 'value' field to Integer then need to sort it.

I also tried below one but giving errors

xyz = A.objects.filter(b__key ="vcount",type = "abc",status = "done").extra(select={'value_int': "CAST(b__value AS UNSIGNED)"}).order_by('-value_int')[:5]

Suggestions or Help will be appreciated.

Answer 1

The .extra() method's select takes SQL, so the column name should be written as SQL b.value .

xyz = A.objects.filter(b__key ="vcount",type = "abc",status = "done")
       .extra(select={'value_int': "CAST(b.value AS UNSIGNED)"})
       .order_by('-value_int')[:5]

Answer 2

Since I'm pretty sure this is the issue I'm going to write it anyway...

I'm guessing that value is a DecimalField which is stored internally as a string for indexing, which is why you are seeing strange ordering.

The solution is to change the type of value from DecimalField to FloatField