DATABASES = {
"default": {
"ENGINE": "django.db.backends.postgresql",
"OPTIONS": {
"service": "my_service",
"passfile": ".my_pgpass",
The PostgreSQL backend passes the content of OPTIONS as keyword
arguments to the connection constructor, allowing for more advanced control
of driver behavior. All available parameters are described in detail in the
PostgreSQL documentation.
Warning
Using a service name for testing purposes is not supported. This
may be implemented later.
Optimizing PostgreSQL’s configuration
Django needs the following parameters for its database connections:
client_encoding: 'UTF8',
default_transaction_isolation: 'read committed' by default,
or the value set in the connection options (see below),
timezone:
- when
USE_TZ is True, 'UTC' by default, or the
TIME_ZONE value set for the connection,
- when
USE_TZ is False, the value of the global
TIME_ZONE setting.
If these parameters already have the correct values, Django won’t set them for
every new connection, which improves performance slightly. You can configure
them directly in postgresql.conf or more conveniently per database
user with ALTER ROLE.
Django will work just fine without this optimization, but each new connection
will do some additional queries to set these parameters.
Isolation level
Like PostgreSQL itself, Django defaults to the READ COMMITTED isolation
level. If you need a higher isolation level such as REPEATABLE READ or
SERIALIZABLE, set it in the OPTIONS part of your database
configuration in DATABASES:
from django.db.backends.postgresql.psycopg_any import IsolationLevel
DATABASES = {
# ...
"OPTIONS": {
"isolation_level": IsolationLevel.SERIALIZABLE,
Under higher isolation levels, your application should be prepared to
handle exceptions raised on serialization failures. This option is
designed for advanced uses.
Changed in Django 4.2: IsolationLevel was added.
Role
New in Django 4.2.
If you need to use a different role for database connections than the role use
to establish the connection, set it in the OPTIONS part of your
database configuration in DATABASES:
DATABASES = {
"default": {
"ENGINE": "django.db.backends.postgresql",
# ...
"OPTIONS": {
"assume_role": "my_application_role",
New in Django 4.2. With psycopg 3.1.8+, Django defaults to the client-side binding
cursors. If you want to use the
server-side binding set it in the
OPTIONS part of your database configuration in
DATABASES:
DATABASES = {
"default": {
"ENGINE": "django.db.backends.postgresql",
# ...
"OPTIONS": {
"server_side_binding": True,
This option is ignored with psycopg2.
Indexes for varchar and text columns
When specifying db_index=True on your model fields, Django typically
outputs a single CREATE INDEX statement. However, if the database type
for the field is either varchar or text (e.g., used by CharField,
FileField, and TextField), then Django will create
an additional index that uses an appropriate PostgreSQL operator class
for the column. The extra index is necessary to correctly perform
lookups that use the LIKE operator in their SQL, as is done with the
contains and startswith lookup types.
Migration operation for adding extensions
If you need to add a PostgreSQL extension (like hstore, postgis, etc.)
using a migration, use the
CreateExtension operation.
Server-side cursors
When using QuerySet.iterator(), Django opens a server-side
cursor. By default, PostgreSQL assumes that
only the first 10% of the results of cursor queries will be fetched. The query
planner spends less time planning the query and starts returning results
faster, but this could diminish performance if more than 10% of the results are
retrieved. PostgreSQL’s assumptions on the number of rows retrieved for a
cursor query is controlled with the cursor_tuple_fraction option.
Transaction pooling and server-side cursors
Using a connection pooler in transaction pooling mode (e.g. PgBouncer)
requires disabling server-side cursors for that connection.
Server-side cursors are local to a connection and remain open at the end of a
transaction when AUTOCOMMIT is True. A
subsequent transaction may attempt to fetch more results from a server-side
cursor. In transaction pooling mode, there’s no guarantee that subsequent
transactions will use the same connection. If a different connection is used,
an error is raised when the transaction references the server-side cursor,
because server-side cursors are only accessible in the connection in which they
were created.
One solution is to disable server-side cursors for a connection in
DATABASES by setting DISABLE_SERVER_SIDE_CURSORS to True.
To benefit from server-side cursors in transaction pooling mode, you could set
up another connection to the database in order to
perform queries that use server-side cursors. This connection needs to either
be directly to the database or to a connection pooler in session pooling mode.
Another option is to wrap each QuerySet using server-side cursors in an
atomic() block, because it disables autocommit
for the duration of the transaction. This way, the server-side cursor will only
live for the duration of the transaction.
Manually-specifying values of auto-incrementing primary keys
Django uses PostgreSQL’s identity columns to store auto-incrementing primary
keys. An identity column is populated with values from a sequence that keeps
track of the next available value. Manually assigning a value to an
auto-incrementing field doesn’t update the field’s sequence, which might later
cause a conflict. For example:
>>> from django.contrib.auth.models import User
>>> User.objects.create(username="alice", pk=1)
<User: alice>
>>> # The sequence hasn't been updated; its next value is 1.
>>> User.objects.create(username="bob")
IntegrityError: duplicate key value violates unique constraint
"auth_user_pkey" DETAIL: Key (id)=(1) already exists.
If you need to specify such values, reset the sequence afterward to avoid
reusing a value that’s already in the table. The sqlsequencereset
management command generates the SQL statements to do that.
Test database templates
You can use the TEST['TEMPLATE'] setting to specify
a template (e.g. 'template0') from which to create a test database.
Speeding up test execution with non-durable settings
You can speed up test execution times by configuring PostgreSQL to be
non-durable.
Warning
This is dangerous: it will make your database more susceptible to data loss
or corruption in the case of a server crash or power loss. Only use this on
a development machine where you can easily restore the entire contents of
all databases in the cluster.
MariaDB notes
Django supports MariaDB 10.4 and higher.
To use MariaDB, use the MySQL backend, which is shared between the two. See the
MySQL notes for more details.
MySQL notes
Version support
Django supports MySQL 8.0.11 and higher.
Django’s inspectdb feature uses the information_schema database, which
contains detailed data on all database schemas.
Django expects the database to support Unicode (UTF-8 encoding) and delegates to
it the task of enforcing transactions and referential integrity. It is important
to be aware of the fact that the two latter ones aren’t actually enforced by
MySQL when using the MyISAM storage engine, see the next section.
Storage engines
MySQL has several storage engines. You can change the default storage engine
in the server configuration.
MySQL’s default storage engine is InnoDB. This engine is fully transactional
and supports foreign key references. It’s the recommended choice. However, the
InnoDB autoincrement counter is lost on a MySQL restart because it does not
remember the AUTO_INCREMENT value, instead recreating it as “max(id)+1”.
This may result in an inadvertent reuse of AutoField
values.
The main drawbacks of MyISAM are that it doesn’t support transactions or
enforce foreign-key constraints.
MySQL DB API Drivers
MySQL has a couple drivers that implement the Python Database API described in
PEP 249:
- mysqlclient is a native driver. It’s the recommended choice.
- MySQL Connector/Python is a pure Python driver from Oracle that does not
require the MySQL client library or any Python modules outside the standard
library.
These drivers are thread-safe and provide connection pooling.
In addition to a DB API driver, Django needs an adapter to access the database
drivers from its ORM. Django provides an adapter for mysqlclient while MySQL
Connector/Python includes its own.
mysqlclient
Django requires mysqlclient 1.4.3 or later.
MySQL Connector/Python
MySQL Connector/Python is available from the download page.
The Django adapter is available in versions 1.1.X and later. It may not
support the most recent releases of Django.
Time zone definitions
If you plan on using Django’s timezone support,
use mysql_tzinfo_to_sql to load time zone tables into the MySQL database.
This needs to be done just once for your MySQL server, not per database.
Creating your database
You can create your database using the command-line tools and this SQL:
CREATE DATABASE <dbname> CHARACTER SET utf8;
This ensures all tables and columns will use UTF-8 by default.
Collation settings
The collation setting for a column controls the order in which data is sorted
as well as what strings compare as equal. You can specify the db_collation
parameter to set the collation name of the column for
CharField and
TextField.
The collation can also be set on a database-wide level and per-table. This is
documented thoroughly in the MySQL documentation. In such cases, you must
set the collation by directly manipulating the database settings or tables.
Django doesn’t provide an API to change them.
By default, with a UTF-8 database, MySQL will use the
utf8_general_ci collation. This results in all string equality
comparisons being done in a case-insensitive manner. That is, "Fred" and
"freD" are considered equal at the database level. If you have a unique
constraint on a field, it would be illegal to try to insert both "aa" and
"AA" into the same column, since they compare as equal (and, hence,
non-unique) with the default collation. If you want case-sensitive comparisons
on a particular column or table, change the column or table to use the
utf8_bin collation.
Please note that according to MySQL Unicode Character Sets, comparisons for
the utf8_general_ci collation are faster, but slightly less correct, than
comparisons for utf8_unicode_ci. If this is acceptable for your application,
you should use utf8_general_ci because it is faster. If this is not acceptable
(for example, if you require German dictionary order), use utf8_unicode_ci
because it is more accurate.
Warning
Model formsets validate unique fields in a case-sensitive manner. Thus when
using a case-insensitive collation, a formset with unique field values that
differ only by case will pass validation, but upon calling save(), an
IntegrityError will be raised.
Connecting to the database
Refer to the settings documentation.
Connection settings are used in this order:
OPTIONS.NAME, USER, PASSWORD, HOST,
- MySQL option files.
In other words, if you set the name of the database in OPTIONS,
this will take precedence over NAME, which would override
anything in a MySQL option file.
Here’s a sample configuration which uses a MySQL option file:
# settings.py
DATABASES = {
"default": {
"ENGINE": "django.db.backends.mysql",
"OPTIONS": {
"read_default_file": "/path/to/my.cnf",
# my.cnf
[client]
database = NAME
user = USER
password = PASSWORD
default-character-set = utf8
Several other MySQLdb connection options may be useful, such as ssl,
init_command, and sql_mode.
Setting sql_mode
The default value of the sql_mode option contains STRICT_TRANS_TABLES.
That option escalates warnings into errors when data are truncated upon
insertion, so Django highly recommends activating a strict mode for MySQL to
prevent data loss (either STRICT_TRANS_TABLES or STRICT_ALL_TABLES).
If you need to customize the SQL mode, you can set the sql_mode variable
like other MySQL options: either in a config file or with the entry
'init_command': "SET sql_mode='STRICT_TRANS_TABLES'" in the
OPTIONS part of your database configuration in DATABASES.
Isolation level
When running concurrent loads, database transactions from different sessions
(say, separate threads handling different requests) may interact with each
other. These interactions are affected by each session’s transaction isolation
level. You can set a connection’s isolation level with an
'isolation_level' entry in the OPTIONS part of your database
configuration in DATABASES. Valid values for
this entry are the four standard isolation levels:
'read uncommitted''read committed''repeatable read''serializable'or None to use the server’s configured isolation level. However, Django
works best with and defaults to read committed rather than MySQL’s default,
repeatable read. Data loss is possible with repeatable read. In particular,
you may see cases where get_or_create()
will raise an IntegrityError but the object won’t appear in
a subsequent get() call.
Creating your tables
When Django generates the schema, it doesn’t specify a storage engine, so
tables will be created with whatever default storage engine your database
server is configured for. The easiest solution is to set your database server’s
default storage engine to the desired engine.
If you’re using a hosting service and can’t change your server’s default
storage engine, you have a couple of options.
After the tables are created, execute an ALTER TABLE statement to
convert a table to a new storage engine (such as InnoDB):
ALTER TABLE <tablename> ENGINE=INNODB;
This can be tedious if you have a lot of tables.
Another option is to use the init_command option for MySQLdb prior to
creating your tables:
"OPTIONS": {
"init_command": "SET default_storage_engine=INNODB",
This sets the default storage engine upon connecting to the database.
After your tables have been created, you should remove this option as it
adds a query that is only needed during table creation to each database
connection.
Table names
There are known issues in even the latest versions of MySQL that can cause the
case of a table name to be altered when certain SQL statements are executed
under certain conditions. It is recommended that you use lowercase table
names, if possible, to avoid any problems that might arise from this behavior.
Django uses lowercase table names when it auto-generates table names from
models, so this is mainly a consideration if you are overriding the table name
via the db_table parameter.
Savepoints
Both the Django ORM and MySQL (when using the InnoDB storage engine) support database savepoints.
If you use the MyISAM storage engine please be aware of the fact that you will
receive database-generated errors if you try to use the savepoint-related
methods of the transactions API. The reason
for this is that detecting the storage engine of a MySQL database/table is an
expensive operation so it was decided it isn’t worth to dynamically convert
these methods in no-op’s based in the results of such detection.
Notes on specific fields
Character fields
Any fields that are stored with VARCHAR column types may have their
max_length restricted to 255 characters if you are using unique=True
for the field. This affects CharField,
SlugField. See the MySQL documentation for more
details.
TextField limitations
MySQL can index only the first N chars of a BLOB or TEXT column. Since
TextField doesn’t have a defined length, you can’t mark it as
unique=True. MySQL will report: “BLOB/TEXT column ‘<db_column>’ used in key
specification without a key length”.
Fractional seconds support for Time and DateTime fields
MySQL can store fractional seconds, provided that the column definition
includes a fractional indication (e.g. DATETIME(6)).
Django will not upgrade existing columns to include fractional seconds if the
database server supports it. If you want to enable them on an existing database,
it’s up to you to either manually update the column on the target database, by
executing a command like:
ALTER TABLE `your_table` MODIFY `your_datetime_column` DATETIME(6)
or using a RunSQL operation in a
data migration.
TIMESTAMP columns
If you are using a legacy database that contains TIMESTAMP columns, you must
set USE_TZ = False to avoid data corruption.
inspectdb maps these columns to
DateTimeField and if you enable timezone support,
both MySQL and Django will attempt to convert the values from UTC to local time.
Row locking with QuerySet.select_for_update()
MySQL and MariaDB do not support some options to the SELECT ... FOR UPDATE
statement. If select_for_update() is used with an unsupported option, then
a NotSupportedError is raised.
When using select_for_update() on MySQL, make sure you filter a queryset
against at least a set of fields contained in unique constraints or only
against fields covered by indexes. Otherwise, an exclusive write lock will be
acquired over the full table for the duration of the transaction.
Automatic typecasting can cause unexpected results
When performing a query on a string type, but with an integer value, MySQL will
coerce the types of all values in the table to an integer before performing the
comparison. If your table contains the values 'abc', 'def' and you
query for WHERE mycolumn=0, both rows will match. Similarly, WHERE mycolumn=1
will match the value 'abc1'. Therefore, string type fields included in Django
will always cast the value to a string before using it in a query.
If you implement custom model fields that inherit from
Field directly, are overriding
get_prep_value(), or use
RawSQL,
extra(), or
raw(), you should ensure that you perform
appropriate typecasting.
SQLite notes
Django supports SQLite 3.27.0 and later.
SQLite provides an excellent development alternative for applications that
are predominantly read-only or require a smaller installation footprint. As
with all database servers, though, there are some differences that are
specific to SQLite that you should be aware of.
Substring matching and case sensitivity
For all SQLite versions, there is some slightly counter-intuitive behavior when
attempting to match some types of strings. These are triggered when using the
iexact or contains filters in Querysets. The behavior
splits into two cases:
1. For substring matching, all matches are done case-insensitively. That is a
filter such as filter(name__contains="aa") will match a name of "Aabb".
2. For strings containing characters outside the ASCII range, all exact string
matches are performed case-sensitively, even when the case-insensitive options
are passed into the query. So the iexact filter will behave exactly
the same as the exact filter in these cases.
Some possible workarounds for this are documented at sqlite.org, but they
aren’t utilized by the default SQLite backend in Django, as incorporating them
would be fairly difficult to do robustly. Thus, Django exposes the default
SQLite behavior and you should be aware of this when doing case-insensitive or
substring filtering.
Decimal handling
SQLite has no real decimal internal type. Decimal values are internally
converted to the REAL data type (8-byte IEEE floating point number), as
explained in the SQLite datatypes documentation, so they don’t support
correctly-rounded decimal floating point arithmetic.
“Database is locked” errors
SQLite is meant to be a lightweight database, and thus can’t support a high
level of concurrency. OperationalError: database is locked errors indicate
that your application is experiencing more concurrency than sqlite can
handle in default configuration. This error means that one thread or process has
an exclusive lock on the database connection and another thread timed out
waiting for the lock the be released.
Python’s SQLite wrapper has
a default timeout value that determines how long the second thread is allowed to
wait on the lock before it times out and raises the OperationalError: database
is locked error.
If you’re getting this error, you can solve it by:
Switching to another database backend. At a certain point SQLite becomes
too “lite” for real-world applications, and these sorts of concurrency
errors indicate you’ve reached that point.
Rewriting your code to reduce concurrency and ensure that database
transactions are short-lived.
Increase the default timeout value by setting the timeout database
option:
"OPTIONS": {
# ...
"timeout": 20,
# ...
This will make SQLite wait a bit longer before throwing “database is locked”
errors; it won’t really do anything to solve them.
QuerySet.select_for_update() not supported
SQLite does not support the SELECT ... FOR UPDATE syntax. Calling it will
have no effect.
Isolation when using QuerySet.iterator()
There are special considerations described in Isolation In SQLite when
modifying a table while iterating over it using QuerySet.iterator(). If
a row is added, changed, or deleted within the loop, then that row may or may
not appear, or may appear twice, in subsequent results fetched from the
iterator. Your code must handle this.
Enabling JSON1 extension on SQLite
To use JSONField on SQLite, you need to enable the
JSON1 extension on Python’s sqlite3 library. If the extension is
not enabled on your installation, a system error (fields.E180) will be
raised.
To enable the JSON1 extension you can follow the instruction on
the wiki page.
The JSON1 extension is enabled by default on SQLite 3.38+.
Oracle notes
Django supports Oracle Database Server versions 19c and higher. Version
1.3.2 or higher of the oracledb Python driver is required.
Deprecated since version 5.0: Support for cx_Oracle is deprecated.
In order for the python manage.py migrate command to work, your Oracle
database user must have privileges to run the following commands:
- CREATE TABLE
- CREATE SEQUENCE
- CREATE PROCEDURE
- CREATE TRIGGER
To run a project’s test suite, the user usually needs these additional
privileges:
- CREATE USER
- ALTER USER
- DROP USER
- CREATE TABLESPACE
- DROP TABLESPACE
- CREATE SESSION WITH ADMIN OPTION
- CREATE TABLE WITH ADMIN OPTION
- CREATE SEQUENCE WITH ADMIN OPTION
- CREATE PROCEDURE WITH ADMIN OPTION
- CREATE TRIGGER WITH ADMIN OPTION
While the RESOURCE role has the required CREATE TABLE,
CREATE SEQUENCE, CREATE PROCEDURE, and CREATE TRIGGER privileges,
and a user granted RESOURCE WITH ADMIN OPTION can grant RESOURCE, such
a user cannot grant the individual privileges (e.g. CREATE TABLE), and thus
RESOURCE WITH ADMIN OPTION is not usually sufficient for running tests.
Some test suites also create views or materialized views; to run these, the
user also needs CREATE VIEW WITH ADMIN OPTION and
CREATE MATERIALIZED VIEW WITH ADMIN OPTION privileges. In particular, this
is needed for Django’s own test suite.
All of these privileges are included in the DBA role, which is appropriate
for use on a private developer’s database.
The Oracle database backend uses the SYS.DBMS_LOB and SYS.DBMS_RANDOM
packages, so your user will require execute permissions on it. It’s normally
accessible to all users by default, but in case it is not, you’ll need to grant
permissions like so:
GRANT EXECUTE ON SYS.DBMS_LOB TO user;
GRANT EXECUTE ON SYS.DBMS_RANDOM TO user;
Connecting to the database
To connect using the service name of your Oracle database, your settings.py
file should look something like this:
DATABASES = {
"default": {
"ENGINE": "django.db.backends.oracle",
"NAME": "xe",
"USER": "a_user",
"PASSWORD": "a_password",
"HOST": "",
"PORT": "",
In this case, you should leave both HOST and PORT empty.
However, if you don’t use a tnsnames.ora file or a similar naming method
and want to connect using the SID (“xe” in this example), then fill in both
HOST and PORT like so:
DATABASES = {
"default": {
"ENGINE": "django.db.backends.oracle",
"NAME": "xe",
"USER": "a_user",
"PASSWORD": "a_password",
"HOST": "dbprod01ned.mycompany.com",
"PORT": "1540",
You should either supply both HOST and PORT, or leave
both as empty strings. Django will use a different connect descriptor depending
on that choice.
Full DSN and Easy Connect
A Full DSN or Easy Connect string can be used in NAME if both
HOST and PORT are empty. This format is required when
using RAC or pluggable databases without tnsnames.ora, for example.
Example of an Easy Connect string:
"NAME": "localhost:1521/orclpdb1"
Example of a full DSN string:
"NAME": (
"(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521))"
"(CONNECT_DATA=(SERVICE_NAME=orclpdb1)))"
Threaded option
If you plan to run Django in a multithreaded environment (e.g. Apache using the
default MPM module on any modern operating system), then you must set
the threaded option of your Oracle database configuration to True:
"OPTIONS": {
"threaded": True,
Failure to do this may result in crashes and other odd behavior.
INSERT … RETURNING INTO
By default, the Oracle backend uses a RETURNING INTO clause to efficiently
retrieve the value of an AutoField when inserting new rows. This behavior
may result in a DatabaseError in certain unusual setups, such as when
inserting into a remote table, or into a view with an INSTEAD OF trigger.
The RETURNING INTO clause can be disabled by setting the
use_returning_into option of the database configuration to False:
"OPTIONS": {
"use_returning_into": False,
In this case, the Oracle backend will use a separate SELECT query to
retrieve AutoField values.
Naming issues
Oracle imposes a name length limit of 30 characters. To accommodate this, the
backend truncates database identifiers to fit, replacing the final four
characters of the truncated name with a repeatable MD5 hash value.
Additionally, the backend turns database identifiers to all-uppercase.
To prevent these transformations (this is usually required only when dealing
with legacy databases or accessing tables which belong to other users), use
a quoted name as the value for db_table:
class LegacyModel(models.Model):
class Meta:
db_table = '"name_left_in_lowercase"'
class ForeignModel(models.Model):
class Meta:
db_table = '"OTHER_USER"."NAME_ONLY_SEEMS_OVER_30"'
Quoted names can also be used with Django’s other supported database
backends; except for Oracle, however, the quotes have no effect.
When running migrate, an ORA-06552 error may be encountered if
certain Oracle keywords are used as the name of a model field or the
value of a db_column option. Django quotes all identifiers used
in queries to prevent most such problems, but this error can still
occur when an Oracle datatype is used as a column name. In
particular, take care to avoid using the names date,
timestamp, number or float as a field name.
NULL and empty strings
Django generally prefers to use the empty string ('') rather than
NULL, but Oracle treats both identically. To get around this, the
Oracle backend ignores an explicit null option on fields that
have the empty string as a possible value and generates DDL as if
null=True. When fetching from the database, it is assumed that
a NULL value in one of these fields really means the empty
string, and the data is silently converted to reflect this assumption.
TextField limitations
The Oracle backend stores TextFields as NCLOB columns. Oracle imposes
some limitations on the usage of such LOB columns in general:
- LOB columns may not be used as primary keys.
- LOB columns may not be used in indexes.
- LOB columns may not be used in a
SELECT DISTINCT list. This means that
attempting to use the QuerySet.distinct method on a model that
includes TextField columns will result in an ORA-00932 error when
run against Oracle. As a workaround, use the QuerySet.defer method in
conjunction with distinct() to prevent TextField columns from being
included in the SELECT DISTINCT list.
Subclassing the built-in database backends
Django comes with built-in database backends. You may subclass an existing
database backends to modify its behavior, features, or configuration.
Consider, for example, that you need to change a single database feature.
First, you have to create a new directory with a base module in it. For
example:
mysite/
mydbengine/
__init__.py
base.py
The base.py module must contain a class named DatabaseWrapper that
subclasses an existing engine from the django.db.backends module. Here’s an
example of subclassing the PostgreSQL engine to change a feature class
allows_group_by_selected_pks_on_model:
mysite/mydbengine/base.py
from django.db.backends.postgresql import base, features
class DatabaseFeatures(features.DatabaseFeatures):
def allows_group_by_selected_pks_on_model(self, model):
return True
class DatabaseWrapper(base.DatabaseWrapper):
features_class = DatabaseFeatures
Finally, you must specify a DATABASE-ENGINE in your settings.py
file:
