How do I make an auto increment integer field in Django

Question

I am making an Order model for a shopping cart and I need to make a field that auto increments when the order is made   class Order models Model       cart   models ForeignKey Cart      add date   models DateTimeField auto now add True      order number   models IntegerField       enable   models BooleanField default True    How do I make the IntegerField auto increment

User · Answer

You can use default primary key  id  which auto increaments   Note  When you use first design i e  use default field  id  as a primary key  initialize object by mentioning column names  e g   class User models Model       user name   models CharField max length   100    then initialize   user   User user name  XYZ     if you initialize in following way   user   User  XYZ     then python will try to set id    XYZ  which will give you error on data type

User · Answer

In Django 1   we have default field with name  quot id quot  which is auto increment  2   You can define a auto increment field using  AutoField field   class Order models Model       auto increment id   models AutoField primary key True       you use primary key   True if you do not want to use default field  id  given by django to your model  db design   ------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------    Table        Create Table                                                                                                                                                     ------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------    core order   CREATE TABLE  core order       auto increment id  int 11  NOT NULL AUTO INCREMENT    PRIMARY KEY   auto increment id     ENGINE InnoDB DEFAULT CHARSET latin1    ------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------  1 row in set  0 01 sec   If you want to use django s default id as increment field    class Order models Model       dd date   models DateTimeField auto now add True       db design   ------------- -----------------------------------------------------------------------------------------------------------------------------------------------------------------    Table         Create Table                                                                                                                                                       ------------- -----------------------------------------------------------------------------------------------------------------------------------------------------------------    core order   CREATE TABLE  core order       id  int 11  NOT NULL AUTO INCREMENT     dd date  datetime NOT NULL    PRIMARY KEY   id     ENGINE InnoDB DEFAULT CHARSET latin1    ------------- -----------------------------------------------------------------------------------------------------------------------------------------------------------------

User · Answer

You can create an autofield  Here is the documentation for the same  Please remember Django won t allow to have more than one AutoField in a model  In your model you already have one for your primary key  which is default   So you ll have to override model s save method and will probably fetch the last inserted record from the table and accordingly increment the counter and add the new record   Please make that code thread safe because in case of multiple requests you might end up trying to insert same value for different new records

User · Answer

In django with every model you will get the by default id field that is auto increament  But still if you manually want to use auto increment  You just need to specify in your Model AutoField   class Author models Model       author id   models AutoField primary key True    you can read more about the auto field in django in Django Documentation for AutoField

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Edited  Fixed mistake in code that stopped it working if there were no YourModel entries in the db   There s a lot of mention of how you should use an AutoField  and of course  where possible you should use that  However there are legitimate reasons for implementing auto-incrementing fields yourself  such as if you need an id to start from 500 or increment by tens for whatever reason   In your models py from django db import models  def from 500                Returns the next default value for the  ones  field      starts from 500               Retrieve a list of  YourModel  instances  sort them by       the  ones  field and get the largest entry     largest   YourModel objects all   order by  ones   last       if not largest            largest is  None  if  YourModel  has no instances           in which case we return the start value of 500         return 500       If an instance of  YourModel  is returned  we get it s        ones  attribute and increment it by 1     return largest ones   1  def add ten            Returns the next default value for the  tens  field          Retrieve a list of  YourModel  instances  sort them by       the  tens  field and get the largest entry     largest   YourModel objects all   order by  tens   last       if not largest            largest is  None  if  YourModel  has no instances           in which case we return the start value of 10         return 10       If an instance of  YourModel  is returned  we get it s        tens  attribute and increment it by 10     return largest tens   10   class YourModel model Model       ones   models IntegerField primary key True                                 default from 500      tens   models IntegerField default add ten

User · Answer

You can override Django save method official doc about it  The modified version of your code  class Order models Model       cart   models ForeignKey Cart      add date   models DateTimeField auto now add True      order number   models IntegerField default 0     changed here     enable   models BooleanField default True       def save self   args    kwargs           self order number   self order number   1         super   save  args    kwargs     Call the  quot real quot  save   method   Another way is to use signals  More one   official Django docs about pre-save stackoverflow example about using pre-save signal

User · Answer

What I needed  A document number with a fixed number of integers that would also act like an AutoField   My searches took me all over incl  this page   Finally I did something like this   I created a table with a DocuNumber field as an IntegerField with foll  attributes    max length 6 primary key True unique True default 100000   The max length value anything as required  and thus the corresponding default  value    A warning is issued while creating the said model  which I could ignore   Afterwards  created a document  dummy  whence as expected  the document had an integer field value of 100000   Afterwards changed the model key field as    Changed the field type as  AutoField Got rid of the max length And defaultattributes Retained the primary key   True attribute   The next  desired document  created had the value as 100001 with subsequent numbers getting incremented by 1   So far so good

User · Answer

class Belly models Model       belly id   models AutoField primary key True      belly name   models CharField max length 50             or          class Belly models Model      belly name   models CharField max length 50    The difference is   The first table has the primary key belly id  specified as AutoField  and second table has the primary key id  implicitly    I think no need to use this directly  a primary key field will automatically be added to your model if you don   t specify  Otherwise  Check the Django Documentation for AutoField for further details related to AutoField

[python] How do I make an auto increment integer field in Django?

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