Added a db_type() method to the database Field class. This is a hook for calculating the database column type for a given Field. Also converted all management.py CREATE TABLE statements to use db_type(), which made that code cleaner. The Field.get_internal_type() hook still exists, but we should consider removing it at some point, because db_type() is more general. Also added docs -- the beginnings of docs on how to create custom database Field classes. This is backwards-compatible.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@5725 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/management.py

@@ -95,19 +95,12 @@ def _get_sequence_list():
 
     return sequence_list
 
-# If the foreign key points to an AutoField, a PositiveIntegerField or a
-# PositiveSmallIntegerField, the foreign key should be an IntegerField, not the
-# referred field type. Otherwise, the foreign key should be the same type of
-# field as the field to which it points.
-get_rel_data_type = lambda f: (f.get_internal_type() in ('AutoField', 'PositiveIntegerField', 'PositiveSmallIntegerField')) and 'IntegerField' or f.get_internal_type()
-
 def get_sql_create(app):
     "Returns a list of the CREATE TABLE SQL statements for the given app."
-    from django.db import get_creation_module, models
+    from django.db import models
+    from django.conf import settings
 
-    data_types = get_creation_module().DATA_TYPES
+    if settings.DATABASE_ENGINE == 'dummy':
-
-    if not data_types:
         # This must be the "dummy" database backend, which means the user
         # hasn't set DATABASE_ENGINE.
         sys.stderr.write(style.ERROR("Error: Django doesn't know which syntax to use for your SQL statements,\n" +
@@ -159,28 +152,19 @@ def _get_sql_model_create(model, known_models=set()):
 
     Returns list_of_sql, pending_references_dict
     """
-    from django.db import backend, get_creation_module, models
+    from django.db import backend, models
-    data_types = get_creation_module().DATA_TYPES
 
     opts = model._meta
     final_output = []
     table_output = []
     pending_references = {}
     for f in opts.fields:
-        if isinstance(f, (models.ForeignKey, models.OneToOneField)):
+        col_type = f.db_type()
-            rel_field = f.rel.get_related_field()
-            while isinstance(rel_field, (models.ForeignKey, models.OneToOneField)):
-                rel_field = rel_field.rel.get_related_field()
-            data_type = get_rel_data_type(rel_field)
-        else:
-            rel_field = f
-            data_type = f.get_internal_type()
-        col_type = data_types[data_type]
         tablespace = f.db_tablespace or opts.db_tablespace
         if col_type is not None:
             # Make the definition (e.g. 'foo VARCHAR(30)') for this field.
             field_output = [style.SQL_FIELD(backend.quote_name(f.column)),
-                style.SQL_COLTYPE(col_type % rel_field.__dict__)]
+                style.SQL_COLTYPE(col_type)]
             field_output.append(style.SQL_KEYWORD('%sNULL' % (not f.null and 'NOT ' or '')))
             if f.unique and (not f.primary_key or backend.allows_unique_and_pk):
                 field_output.append(style.SQL_KEYWORD('UNIQUE'))
@@ -204,7 +188,7 @@ def _get_sql_model_create(model, known_models=set()):
             table_output.append(' '.join(field_output))
     if opts.order_with_respect_to:
         table_output.append(style.SQL_FIELD(backend.quote_name('_order')) + ' ' + \
-            style.SQL_COLTYPE(data_types['IntegerField']) + ' ' + \
+            style.SQL_COLTYPE(models.IntegerField().db_type()) + ' ' + \
             style.SQL_KEYWORD('NULL'))
     for field_constraints in opts.unique_together:
         table_output.append(style.SQL_KEYWORD('UNIQUE') + ' (%s)' % \
@@ -232,9 +216,8 @@ def _get_sql_for_pending_references(model, pending_references):
     """
     Get any ALTER TABLE statements to add constraints after the fact.
     """
-    from django.db import backend, get_creation_module
+    from django.db import backend
     from django.db.backends.util import truncate_name
-    data_types = get_creation_module().DATA_TYPES
 
     final_output = []
     if backend.supports_constraints:
@@ -257,11 +240,9 @@ def _get_sql_for_pending_references(model, pending_references):
     return final_output
 
 def _get_many_to_many_sql_for_model(model):
-    from django.db import backend, get_creation_module
+    from django.db import backend, models
     from django.contrib.contenttypes import generic
 
-    data_types = get_creation_module().DATA_TYPES
-
     opts = model._meta
     final_output = []
     for f in opts.many_to_many:
@@ -275,19 +256,19 @@ def _get_many_to_many_sql_for_model(model):
                 style.SQL_TABLE(backend.quote_name(f.m2m_db_table())) + ' (']
             table_output.append('    %s %s %s%s,' % \
                 (style.SQL_FIELD(backend.quote_name('id')),
-                style.SQL_COLTYPE(data_types['AutoField']),
+                style.SQL_COLTYPE(models.AutoField(primary_key=True).db_type()),
                 style.SQL_KEYWORD('NOT NULL PRIMARY KEY'),
                 tablespace_sql))
             table_output.append('    %s %s %s %s (%s)%s,' % \
                 (style.SQL_FIELD(backend.quote_name(f.m2m_column_name())),
-                style.SQL_COLTYPE(data_types[get_rel_data_type(opts.pk)] % opts.pk.__dict__),
+                style.SQL_COLTYPE(models.ForeignKey(model).db_type()),
                 style.SQL_KEYWORD('NOT NULL REFERENCES'),
                 style.SQL_TABLE(backend.quote_name(opts.db_table)),
                 style.SQL_FIELD(backend.quote_name(opts.pk.column)),
                 backend.get_deferrable_sql()))
             table_output.append('    %s %s %s %s (%s)%s,' % \
                 (style.SQL_FIELD(backend.quote_name(f.m2m_reverse_name())),
-                style.SQL_COLTYPE(data_types[get_rel_data_type(f.rel.to._meta.pk)] % f.rel.to._meta.pk.__dict__),
+                style.SQL_COLTYPE(models.ForeignKey(f.rel.to).db_type()),
                 style.SQL_KEYWORD('NOT NULL REFERENCES'),
                 style.SQL_TABLE(backend.quote_name(f.rel.to._meta.db_table)),
                 style.SQL_FIELD(backend.quote_name(f.rel.to._meta.pk.column)),
@@ -517,7 +498,7 @@ def _emit_post_sync_signal(created_models, verbosity, interactive):
 
 def syncdb(verbosity=1, interactive=True):
     "Creates the database tables for all apps in INSTALLED_APPS whose tables haven't already been created."
-    from django.db import backend, connection, transaction, models, get_creation_module
+    from django.db import backend, connection, transaction, models
     from django.conf import settings
 
     disable_termcolors()
@@ -533,8 +514,6 @@ def syncdb(verbosity=1, interactive=True):
         except ImportError:
             pass
 
-    data_types = get_creation_module().DATA_TYPES
-
     cursor = connection.cursor()
 
     # Get a list of all existing database tables,
@@ -1266,8 +1245,7 @@ runserver.args = '[--noreload] [--adminmedia=ADMIN_MEDIA_PATH] [optional port nu
 
 def createcachetable(tablename):
     "Creates the table needed to use the SQL cache backend"
-    from django.db import backend, connection, transaction, get_creation_module, models
+    from django.db import backend, connection, transaction, models
-    data_types = get_creation_module().DATA_TYPES
     fields = (
         # "key" is a reserved word in MySQL, so use "cache_key" instead.
         models.CharField(name='cache_key', maxlength=255, unique=True, primary_key=True),
@@ -1277,7 +1255,7 @@ def createcachetable(tablename):
     table_output = []
     index_output = []
     for f in fields:
-        field_output = [backend.quote_name(f.name), data_types[f.get_internal_type()] % f.__dict__]
+        field_output = [backend.quote_name(f.name), f.db_type()]
         field_output.append("%sNULL" % (not f.null and "NOT " or ""))
         if f.unique:
             field_output.append("UNIQUE")

django/db/backends/ado_mssql/creation.py

@@ -12,7 +12,6 @@ DATA_TYPES = {
     'ImageField':        'varchar(100)',
     'IntegerField':      'int',
     'IPAddressField':    'char(15)',
-    'ManyToManyField':   None,
     'NullBooleanField':  'bit',
     'OneToOneField':     'int',
     'PhoneNumberField':  'varchar(20)',

django/db/backends/mysql/creation.py

@@ -16,7 +16,6 @@ DATA_TYPES = {
     'ImageField':        'varchar(100)',
     'IntegerField':      'integer',
     'IPAddressField':    'char(15)',
-    'ManyToManyField':   None,
     'NullBooleanField':  'bool',
     'OneToOneField':     'integer',
     'PhoneNumberField':  'varchar(20)',

django/db/backends/mysql_old/creation.py

@@ -16,7 +16,6 @@ DATA_TYPES = {
     'ImageField':        'varchar(100)',
     'IntegerField':      'integer',
     'IPAddressField':    'char(15)',
-    'ManyToManyField':   None,
     'NullBooleanField':  'bool',
     'OneToOneField':     'integer',
     'PhoneNumberField':  'varchar(20)',

django/db/backends/oracle/creation.py

@@ -19,7 +19,6 @@ DATA_TYPES = {
     'ImageField':                   'NVARCHAR2(100)',
     'IntegerField':                 'NUMBER(11)',
     'IPAddressField':               'VARCHAR2(15)',
-    'ManyToManyField':              None,
     'NullBooleanField':             'NUMBER(1) CHECK ((%(column)s IN (0,1)) OR (%(column)s IS NULL))',
     'OneToOneField':                'NUMBER(11)',
     'PhoneNumberField':             'VARCHAR2(20)',

django/db/backends/postgresql/creation.py

@@ -16,7 +16,6 @@ DATA_TYPES = {
     'ImageField':        'varchar(100)',
     'IntegerField':      'integer',
     'IPAddressField':    'inet',
-    'ManyToManyField':   None,
     'NullBooleanField':  'boolean',
     'OneToOneField':     'integer',
     'PhoneNumberField':  'varchar(20)',

django/db/backends/sqlite3/creation.py

@@ -15,7 +15,6 @@ DATA_TYPES = {
     'ImageField':                   'varchar(100)',
     'IntegerField':                 'integer',
     'IPAddressField':               'char(15)',
-    'ManyToManyField':              None,
     'NullBooleanField':             'bool',
     'OneToOneField':                'integer',
     'PhoneNumberField':             'varchar(20)',

django/db/models/fields/__init__.py

@@ -1,3 +1,4 @@
+from django.db import get_creation_module
 from django.db.models import signals
 from django.dispatch import dispatcher
 from django.conf import settings
@@ -117,6 +118,30 @@ class Field(object):
         """
         return value
 
+    def db_type(self):
+        """
+        Returns the database column data type for this field, taking into
+        account the DATABASE_ENGINE setting.
+        """
+        # The default implementation of this method looks at the
+        # backend-specific DATA_TYPES dictionary, looking up the field by its
+        # "internal type".
+        #
+        # A Field class can implement the get_internal_type() method to specify
+        # which *preexisting* Django Field class it's most similar to -- i.e.,
+        # an XMLField is represented by a TEXT column type, which is the same
+        # as the TextField Django field type, which means XMLField's
+        # get_internal_type() returns 'TextField'.
+        #
+        # But the limitation of the get_internal_type() / DATA_TYPES approach
+        # is that it cannot handle database column types that aren't already
+        # mapped to one of the built-in Django field types. In this case, you
+        # can implement db_type() instead of get_internal_type() to specify
+        # exactly which wacky database column type you want to use.
+        data_types = get_creation_module().DATA_TYPES
+        internal_type = self.get_internal_type()
+        return data_types[internal_type] % self.__dict__
+
     def validate_full(self, field_data, all_data):
         """
         Returns a list of errors for this field. This is the main interface,

django/db/models/fields/related.py

@@ -1,6 +1,6 @@
 from django.db import backend, transaction
 from django.db.models import signals, get_model
-from django.db.models.fields import AutoField, Field, IntegerField, get_ul_class
+from django.db.models.fields import AutoField, Field, IntegerField, PositiveIntegerField, PositiveSmallIntegerField, get_ul_class
 from django.db.models.related import RelatedObject
 from django.utils.text import capfirst
 from django.utils.translation import ugettext_lazy, string_concat, ungettext, ugettext as _
@@ -556,6 +556,16 @@ class ForeignKey(RelatedField, Field):
         defaults.update(kwargs)
         return super(ForeignKey, self).formfield(**defaults)
 
+    def db_type(self):
+        # The database column type of a ForeignKey is the column type
+        # of the field to which it points. An exception is if the ForeignKey
+        # points to an AutoField/PositiveIntegerField/PositiveSmallIntegerField,
+        # in which case the column type is simply that of an IntegerField.
+        rel_field = self.rel.get_related_field()
+        if isinstance(rel_field, (AutoField, PositiveIntegerField, PositiveSmallIntegerField)):
+            return IntegerField().db_type()
+        return rel_field.db_type()
+
 class OneToOneField(RelatedField, IntegerField):
     def __init__(self, to, to_field=None, **kwargs):
         try:
@@ -622,6 +632,16 @@ class OneToOneField(RelatedField, IntegerField):
         defaults.update(kwargs)
         return super(OneToOneField, self).formfield(**defaults)
 
+    def db_type(self):
+        # The database column type of a OneToOneField is the column type
+        # of the field to which it points. An exception is if the OneToOneField
+        # points to an AutoField/PositiveIntegerField/PositiveSmallIntegerField,
+        # in which case the column type is simply that of an IntegerField.
+        rel_field = self.rel.get_related_field()
+        if isinstance(rel_field, (AutoField, PositiveIntegerField, PositiveSmallIntegerField)):
+            return IntegerField().db_type()
+        return rel_field.db_type()
+
 class ManyToManyField(RelatedField, Field):
     def __init__(self, to, **kwargs):
         kwargs['verbose_name'] = kwargs.get('verbose_name', None)
@@ -745,6 +765,11 @@ class ManyToManyField(RelatedField, Field):
             defaults['initial'] = [i._get_pk_val() for i in defaults['initial']]
         return super(ManyToManyField, self).formfield(**defaults)
 
+    def db_type(self):
+        # A ManyToManyField is not represented by a single column,
+        # so return None.
+        return None
+
 class ManyToOneRel(object):
     def __init__(self, to, field_name, num_in_admin=3, min_num_in_admin=None,
         max_num_in_admin=None, num_extra_on_change=1, edit_inline=False,

docs/model-api.txt

@@ -981,6 +981,77 @@ See the `One-to-one relationship model example`_ for a full example.
 
 .. _One-to-one relationship model example: http://www.djangoproject.com/documentation/models/one_to_one/
 
+Custom field types
+------------------
+
+**New in Django development version**
+
+Django's built-in field types don't cover every possible database column type --
+only the common types, such as ``VARCHAR`` and ``INTEGER``. For more obscure
+column types, such as geographic polygons or even user-created types such as
+`PostgreSQL custom types`_, you can define your own Django ``Field`` subclasses.
+
+.. _PostgreSQL custom types: http://www.postgresql.org/docs/8.2/interactive/sql-createtype.html
+
+.. admonition:: Experimental territory
+
+    This is an area of Django that traditionally has not been documented, but
+    we're starting to include bits of documentation, one feature at a time.
+    Please forgive the sparseness of this section.
+
+    If you like living on the edge and are comfortable with the risk of
+    unstable, undocumented APIs, see the code for the core ``Field`` class
+    in ``django/db/models/fields/__init__.py`` -- but if/when the innards
+    change, don't say we didn't warn you.
+
+To create a custom field type, simply subclass ``django.db.models.Field``.
+Here is an incomplete list of the methods you should implement:
+
+``db_type()``
+~~~~~~~~~~~~~
+
+Returns the database column data type for the ``Field``, taking into account
+the current ``DATABASE_ENGINE`` setting.
+
+Say you've created a PostgreSQL custom type called ``mytype``. You can use this
+field with Django by subclassing ``Field`` and implementing the ``db_type()``
+method, like so::
+
+    from django.db import models
+
+    class MytypeField(models.Field):
+        def db_type(self):
+            return 'mytype'
+
+Once you have ``MytypeField``, you can use it in any model, just like any other
+``Field`` type::
+
+    class Person(models.Model):
+        name = models.CharField(maxlength=80)
+        gender = models.CharField(maxlength=1)
+        something_else = MytypeField()
+
+If you aim to build a database-agnostic application, you should account for
+differences in database column types. For example, the date/time column type
+in PostgreSQL is called ``timestamp``, while the same column in MySQL is called
+``datetime``. The simplest way to handle this in a ``db_type()`` method is to
+import the Django settings module and check the ``DATABASE_ENGINE`` setting.
+For example::
+
+    class MyDateField(models.Field):
+        def db_type(self):
+            from django.conf import settings
+            if settings.DATABASE_ENGINE == 'mysql':
+                return 'datetime'
+            else:
+                return 'timestamp'
+
+The ``db_type()`` method is only called by Django when the framework constructs
+the ``CREATE TABLE`` statements for your application -- that is, when you first
+create your tables. It's not called at any other time, so it can afford to
+execute slightly complex code, such as the ``DATABASE_ENGINE`` check in the
+above example.
+
 Meta options
 ============