[Solved]-Django save previous object from models



M2M relationships arenโ€™t saved as part of the save() method.
In the admin, the main object is saved, and then the m2m relation is saved; so, by serializing the list of tags in the save method, youโ€™re printing the value of the tags before the new values have been saved.
If you want to install โ€œpost m2m saveโ€ behavior, youโ€™d need to override the update view on the admin itself.

๐Ÿ‘คChristian Frei


You are trying to initialize the ManyToMany attribute (.Servers) when creating the object..

Wherever you try to create the SourceDestinationGroup, you should probably create it THEN do:

group.Servers = servers

Or, remove the Servers attribute in the init method and reset it afterwards:

def __init__(self, *args, **kw):
    super(SourceDestinationGroup, self).__init__(*args, **kw)
    self._temp_Servers = self.Servers

def save(self, **kw):
    if self.id is None:
        self._temp_Servers = self.Servers
        self.Servers = None # Your 'Servers' attribute was still being set, hence raising an Exception in the super.save just after
    super(SourceDestinationGroup, self).save(**kw)
    if self._old_Servers is not None:
        self.Servers = self._temp_Servers 
        super(SourceDestinationGroup, self).save(**kw)


I encountered this problem a few month ago. The m2m relationships are not updated inside the model save method, even if super() is called before using those relationships.

The only workaround Iโ€™ve found is to write a separate function that deals with m2m relationships, and call it from the save method of the form:

def save(self, *args, **kwargs):
    instance = super().save(*args, **kwargs)
    return instance

In your case, this function is the nearly the same as your model save method:

def update_m2m(self):
    if self.Servers != self._old_Servers:
       self.Status = 'C'
       self._old_Servers = self.Servers


Your SourceDestinationGroup instance must be saved to database before you can add any servers to it. You probably can do an easy fix to it in your save method:

def save(self, **kw):
    if self.id is not None and self.Servers != self._old_Servers:
        self.Status = 'C'
        self._old_Servers = self.Servers

    super(SourceDestinationGroup, self).save(**kw)

As I can see, your change of server only makes sense when there are any old values.


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