python - Django: Filter for many to many field gives too many answers? -


have following 4 models

measurement:

class measurement(models.model):     config = models.foreignkey(measurementconfig)        energy = models.foreignkey(energy)        dose = models.decimalfield(max_digits=20,decimal_places=9, blank=true, null=true)

measurementconfig

class measurementconfig(models.model):     date = models.datetimefield(auto_now_add=true)     linac = models.foreignkey(linac)

linac

class linac(models.model):     name = models.charfield(max_length=10)     genre = models.foreignkey(type)     energies = models.manytomanyfield(energy)

energy

class energy(models.model):     value = models.positiveintegerfield()     category = models.foreignkey(energycategory)

now want dose measurements measurement model specific linac , energy.

i have used following code these:

linac = get_object_or_404(linac, name=linacname)     # energies specified linac measurementconfigs = measurementconfig.objects.filter(linac=linac) identifications = [] measurementconfig in measurementconfigs:     identifications.append(measurementconfig.identification) config = get_object_or_404(measurementconfig, identification=identifications[0]) energies = config.linac.energies.all()  # measurements energymeasurements = []     energy in energies:     measurements = measurement.objects.filter(config__linac=linac).filter(config__linac__energies__exact=energy)     energymeasurements.append(measurements)

what expect energymeasurements like this:

energymeasurements = [(measurements_**energy1**), (measurements_**energy2**), (measurements_**energyn**)]

where n amount of energies

but this:

energymeasurements = [(measurements_**allenergies1**), (measurements_**allenergies2**), (measurements_**allenergiesn**)]

where n amount of energies.

so expect query make gets measurements specific energy specified loop. instead measurements energies. i've tried without loop using id of specific energy, same problem occurs.

i know problem in query, can't find out is.

your objective:

now want dose measurements measurement model specific linac , energy.

my approach:

  1. get linac record.
  2. use many-to-many link table appropriate energy record.
  3. get measurementconfig records linked linac record.
  4. for each measurementconfig records, measurement records; use energy record filter record set.

in code posted, looks you're trying filter measurements record set on link doesn't exist, according models specified.

# measurements energymeasurements = []     energy in energies:     measurements = measurement.objects.filter(config__linac=linac).filter(config__linac__energies__exact=energy)     energymeasurements.append(measurements)

a measurement isn't linked linac, think why you're not getting result expect.


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