What is the difference between null True and blank True in Django

Question

When we add a database field in django we generally write   models CharField max length 100  null True  blank True    The same is done with ForeignKey  DecimalField etc  What is the basic difference in having    null True only blank True only null True  blank True   in respect to different  CharField  ForeignKey  ManyToManyField  DateTimeField  fields  What are the advantages disadvantages of using 1 2 3

User · Accepted Answer

null True sets NULL  versus NOT NULL  on the column in your DB  Blank values for Django field types such as DateTimeField or ForeignKey will be stored as NULL in the DB   blank determines whether the field will be required in forms  This includes the admin and your custom forms  If blank True then the field will not be required  whereas if it s False the field cannot be blank   The combo of the two is so frequent because typically if you re going to allow a field to be blank in your form  you re going to also need your database to allow NULL values for that field  The exception is CharFields and TextFields  which in Django are never saved as NULL  Blank values are stored in the DB as an empty string        A few examples   models DateTimeField blank True    raises IntegrityError if blank  models DateTimeField null True    NULL allowed  but must be filled out in a form   Obviously  Those two options don t make logical sense to use  though there might be a use case for null True  blank False if you want a field to always be required in forms  optional when dealing with an object through something like the shell    models CharField blank True    No problem  blank is stored as     models CharField null True    NULL allowed  but will never be set as NULL   CHAR and TEXT types are never saved as NULL by Django  so null True is unnecessary  However  you can manually set one of these fields to None to force set it as NULL  If you have a scenario where that might be necessary  you should still include null True

User · Answer

Null is purely database-related  whereas blank is validation-related  If a field has blank True   validation on Django s admin site will allow entry of an empty value  If a field has blank False   the field will be required

User · Answer

Blank False   this field is required  Null False   this field should not be null  Blank True   this field is optional  Null True   Django uses empty string       not NULL   Note  Avoid using null True on string-based fields such as CharField and TextField and FileField ImageField  Ref  Django null   Django blank

User · Answer

You may have your answer however till this day it s difficult to judge whether to put null True or blank True or both to a field  I personally think it s pretty useless and confusing to provide so many options to developers  Let the handle the nulls or blanks however they want   I follow this table  from Two Scoops of Django

User · Answer

As said in Django Model Field reference  Link     Field options      The following arguments are available to all field types  All are optional             null      Field null If True  Django will store empty values as NULL in the database  Default is False       Avoid using null on string-based fields such as CharField and   TextField because empty string values will always be stored as empty   strings  not as NULL  If a string-based field has null True  that   means it has two possible values for  no data   NULL  and the empty   string  In most cases  it   s redundant to have two possible values for    no data   the Django convention is to use the empty string  not   NULL       For both string-based and non-string-based fields  you will also need   to set blank True if you wish to permit empty values in forms  as   the null parameter only affects database storage  see blank             Note          When using the Oracle database backend  the value NULL will be stored to denote the empty string regardless of this attribute               blank      Field blank       If True  the field is allowed to be blank  Default is False       Note that this is different than null  null is purely   database-related  whereas blank is validation-related  If a field   has blank True  form validation will allow entry of an empty value    If a field has blank False  the field will be required

User · Answer

Simple answer would be  Null is for Database tables while Blank is for Django Forms

User · Answer

Here is an example of the field with blank  True and null True  description   models TextField blank True  null  True   In this case   blank   True  tells our form that it is ok to leave the description field blank  and  null   True  tells our database that it is ok to record a null value in our db field and not give an error

User · Answer

null   True   Means there is no constraint of database for the field to be filled  so you can have an object with null value for the filled that has this option   blank   True   Means there is no constraint of validation in django forms  so when you fill a modelForm for this model you can leave field with this option unfilled

User · Answer

The meaning of null True and blank True in the model also depends on how these fields were defined in the form class    Suppose you have defined the following class   class Client  models Model       name   models CharField  max length 100  blank True      address   models CharField  max length 100  blank False    If the form class has been defined like this   class ClientForm  ModelForm       class Meta          model   Client         fields     name    address           widgets                  name   forms TextInput  attrs     class    form-control form-control-sm                  address   forms TextInput  attrs     class    form-control form-control-sm                Then  the  name  field will not be mandatory  due to the blank True in the model  and the  address  field will be mandatory  due to the blank False in the model    However  if the ClientForm class has been defined like this   class ClientForm  ModelForm       class Meta          model   Client         fields     name    address        name   forms CharField           widget   forms TextInput  attrs     class    form-control form-control-sm               address   forms CharField           widget   forms TextInput  attrs     class    form-control form-control-sm             Then  both fields   name  and  address   will be mandatory   since fields defined declaratively are left as-is   https   docs djangoproject com en 3 0 topics forms modelforms    i e  the default for the  required  attribute of the form field is True and this will require that the fields  name  and  address  are filled  even if  in the model  the field has been set to blank True

User · Answer

If you set null True  it will allow the value of your database column to be set as NULL  If you only set blank True  django will set the default new value for the column equal to  quot  quot   There s one point where null True would be necessary even on a CharField or TextField and that is when the database has the unique flag set for the column  In this case you ll need to use this  a unique string   models CharField blank True  null True  unique True   Preferrably skip the null True for non-unique CharField or TextField  Otherwise some fields will be set as NULL while others as  quot  quot    and you ll have to check the field value for NULL everytime

User · Answer

When you set null true it will set null in your database if the field is not filled  If you set blank  true it will not set any value to the field

User · Answer

null is for database and blank is for fields validation that you want to show on user interface like textfield to get the last name of person  If lastname models charfield  blank true  it didnot ask user to enter last name as this is the optional field now  If lastname models charfield  null true   then it means that if this field doesnot get any value from user then it will store in database as an empty string

User · Answer

In Very simple words   Blank is different than null    null is purely database-related  whereas blank is validation-related required in form     If null True  Django will store empty values as NULL in the database  If a field has blank True  form validation will allow entry of an empty value  If a field has blank False  the field will be required

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This is how the ORM maps blank  amp  null fields for Django 1 8  class Test models Model       charNull          models CharField max length 10  null True      charBlank         models CharField max length 10  blank True      charNullBlank     models CharField max length 10  null True  blank True       intNull           models IntegerField null True      intBlank          models IntegerField blank True      intNullBlank      models IntegerField null True  blank True       dateNull          models DateTimeField null True      dateBlank         models DateTimeField blank True      dateNullBlank     models DateTimeField null True  blank True            The database fields created for PostgreSQL 9 4 are     CREATE TABLE Test     id              serial                    NOT NULL      charNull       character varying 10      charBlank      character varying 10      NOT NULL     charNullBlank  character varying 10       intNull        integer     intBlank       integer                   NOT NULL     intNullBlank   integer      dateNull       timestamp with time zone     dateBlank      timestamp with time zone  NOT NULL     dateNullBlank  timestamp with time zone    CONSTRAINT Test pkey PRIMARY KEY  id      The database fields created for MySQL 5 6 are     CREATE TABLE Test         id             INT 11      NOT  NULL    AUTO INCREMENT         charNull       VARCHAR 10  NULL DEFAULT NULL        charBlank      VARCHAR 10  NOT  NULL        charNullBlank  VARCHAR 10  NULL DEFAULT NULL         intNull        INT 11      NULL DEFAULT NULL        intBlank       INT 11      NOT  NULL        intNullBlank   INT 11      NULL DEFAULT NULL         dateNull       DATETIME    NULL DEFAULT NULL        dateBlank      DATETIME    NOT  NULL        dateNullBlank  DATETIME    NULL DEFAULT NULL

User · Answer

It s crucial to understand that the options in a Django model field definition serve  at least  two purposes  defining the database tables  and defining the default format and validation of model forms   I say  default  because the values can always be overridden by providing a custom form   Some options affect the database  some options affect forms  and some affect both   When it comes to null and blank  other answers have already made clear that the former affects the database table definition and the latter affects model validation  I think the distinction can be made even clearer by looking at use cases for all four possible configurations    null False  blank False  This is the default configuration and means that the value is required in all circumstances  null True  blank True  This means that the field is optional in all circumstances   As noted below  though  this is not the recommended way to make string-based fields optional   null False  blank True  This means that the form doesn t require a value but the database does  There are a number of use cases for this    The most common use is for optional string-based fields  As noted in the documentation  the Django idiom is to use the empty string to indicate a missing value  If NULL was also allowed you would end up with two different ways to indicate a missing value  Another common situation is that you want to calculate one field automatically based on the value of another  in your save   method  say   You don t want the user to provide the value in a form  hence blank True   but you do want the database to enforce that a value is always provided  null False   Another use is when you want to indicate that a ManyToManyField is optional  Because this field is implemented as a separate table rather than a database column  null is meaningless  The value of blank will still affect forms  though  controlling whether or not validation will succeed when there are no relations   null True  blank False  This means that the form requires a value but the database doesn t  This may be the most infrequently used configuration  but there are some use cases for it    It s perfectly reasonable to require your users to always include a value even if it s not actually required by your business logic  After all  forms are only one way of adding and editing data  You may have code that is generating data which doesn t need the same stringent validation that you want to require of a human editor  Another use case that I ve seen is when you have a ForeignKey for which you don t wish to allow cascade deletion  That is  in normal use the relation should always be there  blank False   but if the thing it points to happens to be deleted  you don t want this object to be deleted too  In that case you can use null True and on delete models SET NULL to implement a simple kind of soft deletion

User · Answer

Here  is the main difference of null True and blank True   The default value of both null and blank is False  Both of these values work at field level i e   whether we want to keep a field null or blank   null True will set the field   s value to NULL i e   no data  It is basically for the databases column value   date   models DateTimeField null True    blank True determines whether the field will be required in forms  This includes the admin and your own custom forms   title   models CharField blank True     title can be kept blank   In the database      will be stored  null True blank True This means that the field is optional in all circumstances   epic   models ForeignKey null True  blank True     The exception is CharFields   and TextFields    which in Django are never saved as NULL  Blank values a

User · Answer

When we save anything in Django admin two steps validation happens  on Django level and on Database level  We can t save text in a number field   Database has data type NULL  it s nothing  When Django creates columns in the database it specifies that they can t be empty  And if you will try to save NULL you will get the database error   Also on Django-Admin level  all fields are required by default  you can t save blank field  Django will throw you an error   So  if you want to save blank field you need to allow it on Django and Database level  blank True - will allow empty field in admin panel null True - will allow saving NULL to the database column

User · Answer

null - default is False         if True  Django will store empty as null in the database   blank - default is False         if true that field is allowed to be blank  more  goto https   docs djangoproject com en 3 0 topics db models

User · Answer

The default values of null and blank are False   Null  It is database-related  Defines if a given database column will accept null values or not   Blank  It is validation-related  It will be used during forms validation  when calling form is valid     That being said  it is perfectly fine to have a field with null True and blank False  Meaning on the database level the field can be NULL  but in the application level it is a required field   Now  where most developers get it wrong  Defining null True for string-based fields such as CharField and TextField  Avoid doing that  Otherwise  you will end up having two possible values for    no data     that is  None and an empty string  Having two possible values for    no data    is redundant  The Django convention is to use the empty string  not NULL

User · Answer

Simply null True defines database should accept NULL values  on other hand blank True defines on form validation this field should accept blank values or not If blank True it accept form without a value in that field and blank False default value  on form validation it will show This field is required error   null True False related to database  blank True False related to form validation

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This table below demonstrates the main differences    --------------------------------------------------------------------    Purpose                    null True          blank   True            -------------------------- ------------------ ----------------------    Field can be empty in DB   Do this            Unaffected              -------------------------- ------------------ ----------------------    ModelForm required field   Unaffected         field not required      -------------------------- ------------------ ----------------------    Form Validation            Unaffected         field not required      -------------------------- ------------------ ----------------------    on delete SET NULL         Need this          Unaffected              --------------------------------------------------------------------

[python] What is the difference between null=True and blank=True in Django?

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