Django List field in model

Question

In my model  I want a field that has a list of triplets  e g    1  3  4    4  2  6    8  12  3    3  3  9    Is there a field that can store this data in the database

User · Accepted Answer

You can convert it into string by using JSON and store it as string.

For example,

In [3]: json.dumps([[1, 3, 4], [4, 2, 6], [8, 12, 3], [3, 3, 9]])

Out[3]: '[[1, 3, 4], [4, 2, 6], [8, 12, 3], [3, 3, 9]]'

You can add a method into your class to convert it automatically for you.

import json


class Foobar(models.Model):
    foo = models.CharField(max_length=200)

    def set_foo(self, x):
        self.foo = json.dumps(x)

    def get_foo(self):
        return json.loads(self.foo)

If you're using Django 1.9 and postgresql, there is a new class called JSONField, you should use it instead. Here is a link to it

There is a good talk about PostgreSQL JSONs and Arrays on youtube. Watch it, it has very good information.

User · Answer

If you are using Google App Engine or MongoDB as your backend  and you are using the djangoappengine library  there is a built in ListField that does exactly what you want  Further  it s easy to query the Listfield to find all objects that contain an element in the list

User · Answer

Just use a JSON field that these third-party packages provide    django-jsonfield django-annoying   In this case  you don t need to care about the field value serialization - it ll happen under-the-hood   Hope that helps

User · Answer

You can flatten the list and then store the values to a CommaSeparatedIntegerField  When you read back from the database  just group the values back into threes   Disclaimer  according to database normalization theory  it is better not to store collections in single fields  instead you would be encouraged to store the values in those triplets in their own fields and link them via foreign keys  In the real world  though  sometimes that is too cumbersome slow

User · Answer

If you are using PostgreSQL  you can use ArrayField with a nested ArrayField  https   docs djangoproject com en 2 2 ref contrib postgres fields   This way  the data structure will be known to the underlying database  Also  the ORM brings special functionality for it   Note that you will have to create a GIN index by yourself  though  see the above link  further down  https   docs djangoproject com en 2 2 ref contrib postgres fields  indexing-arrayfield     Edit  updated links to newest Django LTS  this feature exists at least since 1 8

User · Answer

With my current reputation I have no ability to comment  so I choose answer referencing comments for sample code in reply by Prashant Gaur  thanks  Gaur - this was helpful   - his sample is for python2  since python3 has no unicode method    The replacement  below for function get prep value self  value   should work with Django running with python3  I ll use this code soon - yet not tested   Note  though  that I m passing encoding  utf-8   errors  ignore  parameters to decode   and unicode   methods  Encoding should match your Django settings py configuration and passing errors  ignore  is optional  and may result in silent data loss instead of exception whith misconfigured django in rare cases     import sys           def get prep value self  value           if value is None              return value         if sys version info 0     3              if isinstance out data  type b                      return value decode encoding  utf-8   errors  ignore           else              if isinstance out data  type b                      return unicode value  encoding  utf-8   errors  ignore           return str value

User · Answer

I think it will help you    from django db import models import ast  class ListField models TextField         metaclass     models SubfieldBase     description    Stores a python list       def   init   self   args    kwargs           super ListField  self    init    args    kwargs       def to python self  value           if not value              value               if isinstance value  list               return value          return ast literal eval value       def get prep value self  value           if value is None              return value          return unicode value       def value to string self  obj           value   self  get val from obj obj          return self get db prep value value   class ListModel models Model       test list   ListField     Example             ListModel objects create test list    1 2 3    2 3 4 4         ListModel objects get id 1       o   ListModel objects get id 1      o id 1L     o test list   1  2  3    2  3  4  4

User · Answer

If you re on Django 1 10 or newer AND Postgres as your database  you can use  ArrayField  It s better to use than django-taggit or other alternatives  as it s native to the Django framework  https   docs djangoproject com en 3 1 ref contrib postgres fields  arrayfield from django db import models from django contrib postgres fields import ArrayField  class ChessBoard models Model       board   ArrayField          ArrayField              models CharField max length 10  blank True               size 8                     size 8         If you re on Django 3 1 or newer they ve added support for JSONField with most database backends  MariaDB 10 2 7   MySQL 5 7 8   Oracle  PostgreSQL  and SQLite 3 9 0    You can use this to store your Array  https   docs djangoproject com en 3 1 ref models fields  jsonfield from django db import models  class ChessBoard models Model       list of pieces   models JSONField

User · Answer

It s quite an old topic  but since it is returned when searching for  django list field  I ll share the custom django list field code I modified to work with Python 3 and Django 2  It supports the admin interface now and not uses eval  which is a huge security breach in Prashant Gaur s code    from django db import models from typing import Iterable  class ListField models TextField               A custom Django field to represent lists as comma separated strings              def   init   self   args    kwargs           self token   kwargs pop  token                super     init    args    kwargs       def deconstruct self           name  path  args  kwargs   super   deconstruct           kwargs  token     self token         return name  path  args  kwargs      def to python self  value            class SubList list               def   init   self  token   args                   self token   token                 super     init    args               def   str   self                   return self token join self           if isinstance value  list               return value         if value is None              return SubList self token          return SubList self token  value split self token        def from db value self  value  expression  connection           return self to python value       def get prep value self  value           if not value              return         assert isinstance value  Iterable           return self token join value       def value to string self  obj           value   self value from object obj          return self get prep value value

[django] Django: List field in model?

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