Question

I am learning Django (and programming) in my free time. It is fun but I am having an issue with how to logically make a distinction between two models that share a parent.

What I would like to do is have a form where I can enter a machine and a file to send it. The issue I have is that I have two types of machines (they are RS-232 communication) These machines have either hardware flow control or software flow control.

I have set a url /transmitProgram/ to take entered form data and send it to the proper place. I do not know how to select the right machine settings.

OfficeMachine is a hardware flow controlled machine and GarageMachine is software flow controlled

I send in my form to send file 001 to OfficeMachine (how to know if OfficeMachine is software or hardware)

Models.py

class SerialMachine(models.Model):
    EVEN = 1
    ODD = 2
    NONE = 3
    PARITY_CHOICES = (
        (EVEN, "Even"),
        (ODD, "Odd"),
        (NONE, "None"),
    )

    machineName = models.CharField(max_length=50)
    address = models.CharField(max_length=100)
    baudRate = models.IntegerField(max_length=50)
    parity = models.IntegerField(max_length=1, choices=PARITY_CHOICES)
    dataBits = models.IntegerField(max_length=15)
    stopBits = models.IntegerField(max_length=15)
    carriageReturn = models.BooleanField(default=False)
    lineFeed = models.BooleanField(default=True)
    endProgramChar = models.BooleanField(default=True)
    machineServer = models.ForeignKey('SerialPortServer')
    repository = models.ForeignKey('Repository')

    class Meta:
        abstract = True

    def __unicode__(self):
        return self.machineName

class HardwareFlowControlMachine(SerialMachine):
    """
    Represents all CNC machines that are to be connected for a hardware flow
    control connection
    """
    enableRTSCTS = models.BooleanField(default=False) # RTS/CTS Flow Control
    enableDSRDTR = models.BooleanField(default=True) # DSR/DTR Flow Control

class SoftwareFlowControlMachine(SerialMachine):
    """"
    Represents all CNC machines that are to be connected for a software flow
    control connection
    """
    xonChar = models.IntegerField(max_length=2, default=17)
    xoffChar = models.IntegerField(max_length=2, default=19)

My view takes the data from the form and calls a helper function to get the path and machine settings.

Helper.py

def getMachineSettings(machine):
    from django.core.exceptions import ObjectDoesNotExist

    from src.apps.cnc.models import SoftwareFlowControlMachine, HardwareFlowControlMachine

    machineSettings = ""
    try:
        machineSettings = SoftwareFlowControlMachine.get(name_iexact='%s' % machine)
    except ObjectDoesNotExist:
        pass
    if machineSettings == "":
        try:
            machineSettings = HardwareFlowControlMachine.get(name_iexact='%s' % machine)
        except ObjectDoesNotExist:
            pass
    return machineSettings

This just seems like a dumb way to do it though. This post (link) introduced me to the djangosnippets website.

I was looking at this snippet but I am pretty weak in seeing everything fit together.

Am I correct in understanding that if I add inherit ParentModel in my SerialMachine absract class and create a ChildManager that I could just say

machineSettings = SerialMachine.get(name_iexact'%s' % machine)

and from the fields in the inherited classes will be there for me?

Thanks a lot for help and info you can provide for me

Answer 1

See InheritanceManager in django-model-utils, maybe it will fits your needs.