[Answered ]-I have a list of long integers that I assign to a django model charfield. The list of longs get converted to list of unicodes

by

2👍

✅

Based on Django documentation: Writing custom model fields I’ve created simple field LongListAsTextField() which extends default django.db.models.TextField and converts list of longs from and to string with to_python and get_prep_value methods.

models.py

from __future__ import absolute_import

from django.db import models

from .fields import LongListAsTextField

class Record(models.Model):
    parent_list = LongListAsTextField()

fields.py

from django.db import models

from django.utils.six import with_metaclass

class LongListAsTextField(with_metaclass(models.SubfieldBase, models.TextField)):

    def to_python(self, value):
        if isinstance(value, list):
           return value

        return [
            long(val)
            for val in value.split(',')
            if val.isdigit()
        ]

    def get_prep_value(self, value):
        return ','.join([str(val) for val in value])

shell

Record(parent_list=[1,2]).save()
record = Record.objects.last()
record.parent_list # returns [1L, 2L]
👤daniula

0👍

Django does handle serialisation and storage of your list of longs into your database CharField field without you doing anything. You don’t need a custom field; CharField will convert the list using bytes(), convert that to UTF8, and store it in your database. Your list may contain strings, numbers, tuples, lists, dicts, booleans, and None, or combinations thereof.

The problem you have is that when you retrieve the list from the database, it will be a unicode string, not a Python list. No problem, provided that you limit your data types to those mentioned above, you can use ast.literal_eval() to safely unmarshall the list:

In your_app/models.py:

from django.db import models

class List(models.Model):
    the_list = models.CharField(max_length=300, blank=True)

Then in python manage.py shell:

>>> import ast
>>> from your_app.models import List

>>> original_list = [1, 2, 3, 444L, 1100L, -1234, 11.72, 'hi there', u'\u3030\u3000', {'a': 1, 'b': 2, 'c': [1, 2, 3]}, ('this', 'is', 'a', 'tuple'), True, None]
>>> List(the_list=original_list).save()
>>> retrieved_list = List.objects.last()
>>> retrieved_list
u"[1, 2, 3, 444L, 1100L, -1234, 11.72, 'hi there', u'\\u3030\\u3000', {'a': 1, 'c': [1, 2, 3], 'b': 2}, ('this', 'is', 'a', 'tuple'), True, None]"
>>> original_list == ast.literal_eval(retrieved_list.the_list)
True

Which shows that the list was successfully round-tripped through the database.

👤mhawke

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