了解 Django JSONField 键路径查询和详尽集
Understanding Django JSONField key-path queries and exhaustive sets
在 querying JSONField 上查看 Django 文档时，我看到一条说明：
Due to the way in which key-path queries work, exclude() and filter() are not guaranteed to produce exhaustive sets. If you want to include objects that do not have the path, add the isnull lookup.
谁能给我一个不会产生详尽集的查询示例？我很难想出一个。
这是导致您引用的文档的票证：https://code.djangoproject.com/ticket/31894
TL;DR: 要在 JSON 键路径上获得 .filter() 的逆，仅使用 [=13= 是不够的] 使用相同的子句，因为它只会为您提供 JSON 关键路径存在但具有不同值的记录，而不是 JSON 关键路径根本不存在的记录。这就是为什么它说：
If you want to include objects that do not have the path, add the isnull lookup.
如果我可以在这里引用门票描述：
Filtering based on a JSONField key-value pair seems to have some
unexpected behavior when involving a key that not all records have.
Strangely, filtering on an optional property key will not return the
inverse result set that an exclude on the same property key will
return.
In my database, I have:
- 2250 total records 49 records where jsonfieldname = {'propertykey': 'PropertyValue'}
- 296 records where jsonfieldname has a 'propertykey' key with some other value
- 1905 records where jsonfieldname does not have a 'propertykey' key at all
The following code:
q = Q(jsonfieldname__propertykey="PropertyValue")
total_records = Record.objects.count()
filtered_records = Record.objects.filter(q).count()
excluded_records = Record.objects.exclude(q).count()
filtered_plus_excluded_records = filtered_records + excluded_records
print('Total: %d' % total_records)
print('Filtered: %d' % filtered_records)
print('Excluded: %d' % excluded_records)
print('Filtered Plus Excluded: %d' % filtered_plus_excluded_records)
Will output this:
Total: 2250
Filtered: 49
Excluded: 296
Filtered Plus Excluded: 345
It is surprising that the filtered+excluded value is not equal to the total record count. It's surprising that the union of a expression plus its inverse does not equal the sum of all records. I am not aware of any other queries in Django that would return a result like this. I realize adding a check that the key exists would return a more expected results, but that doesn't stop the above from being surprising.
I'm not sure what a solution would be - either a note in the documentation that this behavior should be expected, or take a look at how this same expression is applied for both the exclude() and filter() queries and see why they are not opposites.
在 querying JSONField 上查看 Django 文档时，我看到一条说明：
Due to the way in which key-path queries work, exclude() and filter() are not guaranteed to produce exhaustive sets. If you want to include objects that do not have the path, add the
isnulllookup.
谁能给我一个不会产生详尽集的查询示例？我很难想出一个。
这是导致您引用的文档的票证：https://code.djangoproject.com/ticket/31894
TL;DR: 要在 JSON 键路径上获得 .filter() 的逆，仅使用 [=13= 是不够的] 使用相同的子句，因为它只会为您提供 JSON 关键路径存在但具有不同值的记录，而不是 JSON 关键路径根本不存在的记录。这就是为什么它说：
If you want to include objects that do not have the path, add the isnull lookup.
如果我可以在这里引用门票描述：
Filtering based on a JSONField key-value pair seems to have some unexpected behavior when involving a key that not all records have. Strangely, filtering on an optional property key will not return the inverse result set that an exclude on the same property key will return.
In my database, I have:
- 2250 total records 49 records where jsonfieldname = {'propertykey': 'PropertyValue'}
- 296 records where jsonfieldname has a 'propertykey' key with some other value
- 1905 records where jsonfieldname does not have a 'propertykey' key at all
The following code:
q = Q(jsonfieldname__propertykey="PropertyValue") total_records = Record.objects.count() filtered_records = Record.objects.filter(q).count() excluded_records = Record.objects.exclude(q).count() filtered_plus_excluded_records = filtered_records + excluded_records print('Total: %d' % total_records) print('Filtered: %d' % filtered_records) print('Excluded: %d' % excluded_records) print('Filtered Plus Excluded: %d' % filtered_plus_excluded_records)Will output this:
Total: 2250 Filtered: 49 Excluded: 296 Filtered Plus Excluded: 345It is surprising that the filtered+excluded value is not equal to the total record count. It's surprising that the union of a expression plus its inverse does not equal the sum of all records. I am not aware of any other queries in Django that would return a result like this. I realize adding a check that the key exists would return a more expected results, but that doesn't stop the above from being surprising.
I'm not sure what a solution would be - either a note in the documentation that this behavior should be expected, or take a look at how this same expression is applied for both the exclude() and filter() queries and see why they are not opposites.