I know this question has been asked a couple of time but no previous answer was able to solve my problem.
I had a perfectly working model in Django that looked like this:
class Template(models.Model):
mat = models.CharField(max_length=50, null=True)
...
I had many instances of this model and up to now I was very happy with it. I recently decided that instead of a Charfield, this model was better suited to work with a ForeignKey in this position instead.
To get into details, the attribute ''mat'' was previously only referring to the name of another object instance. I decided to change it to the full fledged instance with a ForeignKey instead, like it should have always been. Therefore, the model was modified as follows:
class Template(models.Model):
mat = models.ForeignKey(Stock, on_delete=models.CASCADE, related_name='mat_stock', verbose_name="mat", null=True)
...
I followed this change with the regular */manage.py makemigrations, */manage.py migrate. While these two commands worked, I was unable to select any instance of Template in the shell without raising the following error:
OperationalError: (1054, "Unknown column 'myapp_template.mat_id' in 'field list'")
Similar situations I encountered were solved by manually adding a column in SQL with the following line:
ALTER TABLE database.myapp_template ADD mat INT;
Unfortunately this did not solve my problem.
I figured maybe the problem was that I already had instances of my object that had character values in the ''mat'' column. Django would expect integer values (specifically "id") after my migration, so I decided to create a completely new attribute for Template as follows:
class Template(models.Model):
pos_mat = models.ForeignKey(Stock, on_delete=models.CASCADE, related_name='mat_stock', verbose_name="mat", null=True)
...
This, I thought, would delete (or disregard) the "mat" column and create new "pos_mat" columns with the desired properties without having to handle old character values that wouldn't fit with the requirements. From there on it should be like adding a completely new ForeignKey attribute.
After the required and successful */manage.py makemigrations, */manage.py migrate I am still unable to access an instance of my model in the shell. I still get the same unpleasing:
OperationalError: (1054, "Unknown column 'myapp_template.mat_id' in 'field list'")
Would anybody know how to convince Django to go along with my changes? I am skeptical that rolling back migrations to zero will help me (it did not solve my problems in the past) and I hope it will not come to the deletion of my data. It is acceptable for my model to have an empty field in this column since I added a null=True to my attribute.
Thank you very much for your help. Have a good day.
