unexpected JSONField behavior clarification - key value pairs initially loaded integers, then saved down as strings into the database

[Oliver Zhou]

Using Django 1.11, Python 2.7, PostGres, and JSONField I'm getting behavior I don't expect.

It seems when JSONField values are initially saved/accessed in memory, they're python "integers", but when saved to the database and then re-accessed, the values are now in string format.

What about how Django handles JSONField string vs integers am I missing here? Whats the best way to get deterministic behavior here? 

Am I supposed to always, say, use json.dumps to work with this stuff in string format? Should I be converting all JSONField values before trying to access any values?

Example 1 - Basic Problem

Example Model :

class ExampleModel(models.Model):
    external_ids = JSONField(blank=True, null=True, default=dict)

My code:

new_example = ExampleModel.objects.create()
new_example.external_ids[1234] = {}
print(new_example.external_ids)

Output looks like this : 

{1234: {}}

I can now access values stored like this :

In [140]: new_example.external_ids[1234]
Out[140]: {}

I will now then save the object to the database

new_example.save()

However, when I go back and try to access the fields again, all integer values in the JSON have been converted into strings, and I cannot access them anymore without getting a KeyError

reload_example = ExampleModel.objects.get(id=1)
reload_example.external_ids[1234]
In [144]: reload_example.external_ids[1234]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-147-064b4b6a1511> in <module>()
----> 1 reload_example.external_ids[1234]
KeyError: 1234

By this time, the integer 1234 has been converted into a string that looks like something like the following :  Why is this?

In [147]: print(reload_example.external_ids)
Out[147]: {u'1234': {}}

Therefore, at this time, I have to do this to access the fields : Whats the correct way to handle this?

In [160]: c2.external_ids[str(1234)]
Out[160]: {}

Example 2 - Non-deterministic Merge Problem - 

In fact, this creates some other interesting problems for me too, where integer keys and string keys get merged together in uncertain order as well.

I create a new model - and save some key value pairs down into the JSONField:

In [164]: example2 = ExampleModel.objects.create()
In [165]: example2.external_ids
Out[165]: {}
In [166]: example2.external_ids[1234] = {'567': '890'}
In [167]: example2.save()
In [169]: example2.external_ids
Out[169]: {1234: {'567': '890'}}

Then I try to reload the model back into memory :

In [170]: reload_example2 = ExampleModel.objects.get(id=2)
In [171]: reload_example2.external_ids
Out[171]: {u'1234': {u'567': u'890'}}

Then I try to save a new set of values for key 1234:

In [172]: reload_example2.external_ids[1234] = {'890': '567'}
In [173]: reload_example2.external_ids
Out[173]: {1234: {'890': '567'}, u'1234': {u'567': u'890'}}

Now it seems like both key value pairs are loaded into memory - just the older one is tracked by a string-ified key, and the new values are tracked by an integer-based key

In [174]: reload_example2.save()

Then I save and reload the model again - it seems uncertain which values actually got saved down - whats the expectation here?

In [175]: reload_example3 = ExampleModel.objects.get(id=2)
In [176]: reload_example3.external_ids
Out[176]: {u'1234': {u'890': u'567'}}

Thanks!
Oliver

[Peter of the Norse]

This is actually part of the JSON specification.  All of the keys must be strings.  If you put in an int or float, it will automatically convert it, but that is something you have to watch out for since it can lead to data loss.

>>> import json

>>> test = {4: 5, '4': 'a'}

>>> json.loads(json.dumps(test))

{'4': 5} 

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Peter of the Norse

Rahm...@Radio1190.org

[Oliver Zhou]

Thanks for the reply! I accidentally posted this twice. Still seems like it should raise some sort of warning or exception when you're trying to edit both an integer key and a string key at the same time, instead of just allowing for seemingly non-deterministic data loss.