#28857: PostgreSQL Cast function shortcut
-------------------------------------+-------------------------------------
Reporter: Jurica Železnjak | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Keywords: postgres,orm | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0
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Comment (by Jurica Železnjak):
models.py
{{{
from django.contrib.postgres.fields import JSONField
class SensorData(BaseModel):
timestamp = models.DateTimeField()
data = JSONField()
""" sample value for data: {
"Temperature": 19.9,
"Relative Humidity": 29.4,
"PM2.5": 9.8,
"TVOC": 79.0,
"CO2": 476.0,
"CO": 0.0,
"Air Pressure": 977.1,
"Ozone": 21.3,
"NO2": 68.1,
"Timestamp": 1511770361,
"DateTime": "2017-11-27 09:12"
}
"""
}}}
{{{
from django.db.models.functions import Cast
from django.db.models import Func, Avg, FloatField
class ObjectAtPath(Func):
function = '#>>'
template = "%(expressions)s%(function)s'{%(path)s}'"
arity = 1
def __init__(self, expression, path, **extra):
# if path is a list, convert it to a comma separated string
if isinstance(path, (list, tuple)):
path = ','.join(path)
super().__init__(expression, path=path, **extra)
SensorData.objects.all().aggregate(temp=Avg(Cast(ObjectAtPath('data',
'Temperature'), output_field=FloatField())))
}}}
I think this should be enough to reproduce the error.
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Ticket URL: <https://code.djangoproject.com/ticket/28857#comment:2>
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