How to filter datetime field +/- datetime using SQLalchemy

Question

I have a mysql table representing editorial articles and their metadata like title, author, and datecreated.

I have another table representing metrics (such as view counts) about those articles computed at different time points. Each row is a recording of these metrics for a particular article at a particular moment in time.

I want to retrieve all rows of the metrics table where the metric row timestamp field is within a period of two hours occurring after one hour past the related article's datecreated field. I'd like to do this using SQLalchemy.

My current SQLalchemy query looks like this:

import sqlalchemy as sa
import models as m

s = session()
q = (s.query(m.Article.fb_shares, func.avg(m.ArticlesMetric.views)),
 .join(m.ArticlesMetric)
 .filter(sa.between(m.ArticlesMetric.tstamp,
         m.Article.created + timedelta(hours=1),
         m.Article.created + timedelta(hours=3))
        )
 .group_by(m.Article.id))

result = q.all()
s.close()

However, this results in the following error:

Warning: (1292, u"Truncated incorrect DOUBLE value: '1970-01-01 05:30:00'")

mySQL internally casts data of different types to doubles before making a comparison when a comparison is attempted between different types. I believe this error is somehow a result of using the timedelta, but I'm not sure how else I can achieve what I'm trying to do. Any suggestions very welcome.

Answer 1

Actually, this is harder than it looks. If you had done this in MySQL directly, this is what you would have written:

SELECT ...
FROM ...
JOIN ...
WHERE tstamp BETWEEN DATE_ADD(created, INTERVAL 1 HOUR) AND DATE_ADD(created, INTERVAL 3 HOUR)
GROUP BY ...

And you have to do more or less the same thing with SQLAlchemy, simply because m.Article.created is not a constant.

If you enable query logging, you can see the MySQL query generated by your code, and see that it does not correspond to what you would have thought:

INFO:sqlalchemy.engine.base.Engine:SELECT test.id AS test_id, test.dt AS test_dt, test.tp AS test_tp 
FROM test 
WHERE test.tp BETWEEN test.dt + %(dt_1)s AND test.dt + %(dt_2)s
INFO:sqlalchemy.engine.base.Engine:{'dt_1': datetime.datetime(1970, 1, 1, 1, 0), 'dt_2': datetime.datetime(1970, 1, 1, 3, 0)}

---

I managed to find a way to do what you want, here is the code:

from sqlalchemy.sql import func
from sqlalchemy.sql.expression import text

...
filter(sa.between(m.ArticlesMetric.tstamp,
     func.date_add(m.Article.created, text('INTERVAL 1 HOUR')),
     func.date_add(m.Article.created, text('INTERVAL 3 HOUR')))