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python - How to deal with "partial" dates (2010-00-00) from MySQL in Django?

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up vote 6 down vote favorite 1 In one of my Django projects that use MySQL as the database, I need to have a date fields that accept also "partial" dates like only year (YYYY) and year and month (YYYY-MM) plus normal date (YYYY-MM-DD). The date field in MySQL can deal with that by accepting 00 for the month and the day. So 2010-00-00 is valid in MySQL and it represent 2010. Same thing for 2010-05-00 that represent May 2010. So I started to create a PartialDateField to support this feature. But I hit a wall because, by default, and Django use the default, MySQLdb, the python driver to MySQL, return a object for a date field AND support only real date. So it's possible to modify the converter for the date field used by MySQLdb and return only a string in this format 'YYYY-MM-DD'. Unfortunately the converter use by MySQLdb is set at the connection level so it's use for all MySQL date fields. But Django DateField rely on the fact that the database return a object, so if I change the converter to return a string, Django is not happy at all. Someone have an idea or advice to solve this problem? How to create a PartialDateField in Django ? EDIT Also I should add that I already thought of 2 solutions, create 3 integer fields for year, month and day (as mention by Alison R.) or use a varchar field to keep date as string in this format YYYY-MM-DD. But in both solutions, if I'm not wrong, I will loose the special properties of a date field like doing query of this kind on them: Get all entries after this date. I can probably re-implement this functionality on the client side but that will not be a valid solution in my case because the database can be query from other systems (mysql client, MS Access, etc.) python mysql database django date
  this question edited Jun 4 '10 at 13:26 asked Jun 4 '10 at 2:49 Etienne 8,591 4 27 38

 |  5 Answers

up vote 4 down vote ---Accepted---Accepted---Accepted---

First, thanks for all your answers. None of them, as is, was a good solution for my problem, but, for your defense, I should add that I didn't give all the requirements. But each one help me think about my problem and some of your ideas are part of my final solution. So my final solution, on the DB side, is to use a varchar field (limited to 10 chars) and storing the date in it, as a string, in the ISO format (YYYY-MM-DD) with 00 for month and day when there's no month and/or day (like a date field in MySQL). This way, this field can work with any databases, the data can be read, understand and edited directly and easily by a human using a simple client (like mysql client, phpmyadmin, etc.). That was a requirement. It can also be exported to Excel/CSV without any conversion, etc. The disadvantage is that the format is not enforce (except in Django). Someone could write 'not a date' or do a mistake in the format and the DB will accept it (if you have an idea about this problem...). This way it's also possible to do all of the special queries of a date field relatively easily. For queries with WHERE: <, >, <=, >= and = work directly. The IN and BETWEEN queries work directly also. For querying by day or month you just have to do it with EXTRACT (DAY|MONTH ...). Ordering work also directly. So I think it covers all the query needs and with mostly no complication. On the Django side, I did 2 things. First, I have created a PartialDate object that look mostly like but supporting date without month and/or day. Inside this object I use a datetime.datetime object to keep the date. I'm using the hours and minutes as flag that tell if the month and day are valid when they are set to 1. It's the same idea that steveha propose but with a different implementation (and only on the client side). Using a datetime.datetime object gives me a lot of nice features for working with dates (validation, comparaison, etc.). Secondly, I have created a PartialDateField that mostly deal with the conversion between the PartialDate object and the database. So far, it works pretty well (I have mostly finish my extensive unit tests).
  this answer answered Jun 12 '10 at 3:50 Etienne 8,591 4 27 38      This seems like a very good solution. I don't like the trick of using the hours and minutes as a flag, because I am worried that someday you might need to use them to actually store hours and minutes, and then you will have a problem. But if that day never comes, then I am worried about nothing! –  steveha Jun 15 '10 at 3:32      If you ever need to extend this to handle hours, minutes, seconds, etc. I suggest you use RFC 3339 standard, as it
 s the same virtues as your solution (works with any database, human readable, etc.) –  steveha Jun 15 '10 at 3:36      Thanks for the info about the RFC! I agree that using the hours and minutes as flag is the only hackish part of my solution but its making things so simple for sorting, etc. If I need time in the futur, I will create a new PartialDateTime object (not a PartialDate) with an other implementation. But honestly I have hard time to see the use case for this? –  Etienne Jun 15 '10 at 15:35      Here appears to be an implementation of this approach:… –  blueyed Nov 22 '13 at 12:23

 |  up vote 1 down vote You could store the partial date as an integer (preferably in a field named for the portion of the date you are storing, such as year, month or day) and do validation and conversion to a date object in the model. EDIT If you need real date functionality, you probably need real, not partial, dates. For instance, does "get everything after 2010-0-0" return dates inclusive of 2010 or only dates in 2011 and beyond? The same goes for your other example of May 2010. The ways in which different languages/clients deal with partial dates (if they support them at all) are likely to be highly idiosyncratic, and they are unlikely to match MySQL's implementation. On the other hand, if you store a year integer such as 2010, it is easy to ask the database for "all records with year > 2010" and understand exactly what the result should be, from any client, on any platform. You can even combine this approach for more complicated dates/queries, such as "all records with year > 2010 AND month > 5". SECOND EDIT Your only other (and perhaps best) option is to store truly valid dates and come up with a convention in your application for what they mean. A DATETIME field named like date_month could have a value of 2010-05-01, but you would treat that as representing all dates in May, 2010. You would need to accommodate this when programming. If you had date_month in Python as a datetime object, you would need to call a function like date_month.end_of_month() to query dates following that month. (That is pseudocode, but could be easily implemented with something like the calendar module.)
  this answer edited Jun 4 '10 at 14:38 answered Jun 4 '10 at 2:54 Alison R. 3,108 16 29      I already thought of this solution but I think it will not work in my case. See my EDIT. –  Etienne Jun 4 '10 at 3:29

 |  up vote 1 down vote It sounds like you want to store a date interval. In Python this would (to my still-somewhat-noob understanding) most readily be implemented by storing two datetime.datetime objects, one specifying the start of the date range and the other specifying the end. In a manner similar to that used to specify list slices, the endpoint would not itself be included in the date range. For example, this code would implement a date range as a named tuple: >>> from datetime import datetime

>>> from collections import namedtuple

>>> DateRange = namedtuple('DateRange', 'start end')

>>> the_year_2010 = DateRange(datetime(2010, 1, 1), datetime(2011, 1, 1))

>>> the_year_2010.start <= datetime(2010, 4, 20) < the_year_2010.end


>>> the_year_2010.start <= datetime(2009, 12, 31) < the_year_2010.end


>>> the_year_2010.start <= datetime(2011, 1, 1) < the_year_2010.end


Or even add some magic: >>> DateRange.__contains__ = lambda self, x: self.start <= x < self.end

>>> datetime(2010, 4, 20) in the_year_2010


>>> datetime(2011, 4, 20) in the_year_2010


This is such a useful concept that I'm pretty sure that somebody has already made an implementation available. For example, a quick glance suggests that the relativedate class from the dateutil package will do this, and more expressively, by allowing a 'years' keyword argument to be passed to the constructor. However, mapping such an object into database fields is somewhat more complicated, so you might be better off implementing it simply by just pulling both fields separately and then combining them. I guess this depends on the DB framework; I'm not very familiar with that aspect of Python yet. In any case, I think the key is to think of a "partial date" as a range rather than as a simple value. edit It's tempting, but I think inappropriate, to add more magic methods that will handle uses of the > and < operators. There's a bit of ambiguity there: does a date that's "greater than" a given range occur after the range's end, or after its beginning? It initially seems appropriate to use <= to indicate that the date on the right-hand side of the equation is after the start of the range, and < to indicate that it's after the end. However, this implies equality between the range and a date within the range, which is incorrect, since it implies that the month of May, 2010 is equal to the year 2010, because May the 4th, 2010 equates to the both of them. IE you would end up with falsisms like 2010-04-20 == 2010 == 2010-05-04 being true. So probably it would be better to implement a method like isafterstart to explicitly check if a date is after the beginning of the range. But again, somebody's probably already done it, so it's probably worth a look on pypi to see what's considered production-ready. This is indicated by the presence of "Development Status :: 5 - Production/Stable" in the "Categories" section of a given module's pypi page. Note that not all modules have been given a development status. Or you could just keep it simple, and using the basic namedtuple implementation, explicitly check >>> datetime(2012, 12, 21) >= the_year_2010.start


  this answer edited Jun 4 '10 at 23:42 answered Jun 4 '10 at 23:00 intuited 12.4k 3 38 66      I definitely not storing time intervals. This PartialDate will be use to store mostly birthday dates for peoples, dead and alive. So, frequently, especially for dead peoples, my client do not have the complete date. But it help me in my development to "think of a "partial date" as a range". –  Etienne Jun 12 '10 at 3:55

 |  up vote 0 down vote Can you store the date together with a flag that tells how much of the date is valid? Something like this: YEAR_VALID = 0x04


DAY_VALID = 0x01




Then, if you have a date like 2010-00-00, convert that to 2010-01-01 and set the flag to Y_VALID. If you have a date like 2010-06-00, convert that to 2010-06-01 and set the flag to YM_VALID. So, then, PartialDateField would be a class that bundles together a date and the date-valid flag described above. P.S. You don't actually need to use the flags the way I showed it; that's the old C programmer in me coming to the surface. You could use Y_VALID, YM_VALID, YMD_VALID = range(3) and it would work about as well. The key is to have some kind of flag that tells you how much of the date to trust.
  this answer edited Jun 15 '10 at 3:29 answered Jun 4 '10 at 5:22 steveha 43.1k 11 67 94      This answer doesn't address the fact that Python doesn't consider something like 2010-00-00 a valid date (even if MySQL does). How do you suggest he store and retrieve that? –  Alison R. Jun 4 '10 at 14:25      This answer suggests that he convert such a date to 2010-01-01. Look, it's in there, I didn't just edit that. MySQL has a feature where you can store weird partial dates, but Python doesn't understand them, so I am specifically recommending not using the weird partial dates, but rather using dates and a flag that says how much of the date you can actually trust. You don't actually need to use the flags the way I showed it; that's the old C programmer in me coming to the surface. You could use Y_VALID, YM_VALID, YMD_VALID = range(3) and it would work about as well. –  steveha Jun 6 '10 at 6:12      Fair enough. I can't revoke my downvote unless the answer is edited, unfortunately. (P.S. this indeed seems like a rather C-ish solution ;) –  Alison R. Jun 10 '10 at 21:11      Okay, I'll edit the answer! –  steveha Jun 15 '10 at 3:28

 |  up vote 0 down vote Although not in Python - here's an example of how the same problem was solved in Ruby - using a single Integer value - and bitwise operators to store year, month and day - with month and day optional. Look at the source in lib for date.rb and bits.rb. I'm sure a similar solution could be written in Python. To persist the date (sortable) you just save the Integer to the database.
  this answer answered May 28 '12 at 18:00 Blue Waters 368 1 2 14


up vote 6 down vote favorite 1 In one of my Django projects that use MySQL as the database, I need to have a date fields that accept also "partial" dates like only year (








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