Fixed #19716 -- Added support for microseconds with MySQL 5.6.4 and up

Thanks erik@cederstrand.dk for the report and Tim Graham for the review.

4 files changed, 42 insertions, 8 deletions

diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index f0e184dde3..fcdee1bbd3 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -79,7 +79,7 @@ def adapt_datetime_with_timezone_support(value, conv):
             default_timezone = timezone.get_default_timezone()
             value = timezone.make_aware(value, default_timezone)
         value = value.astimezone(timezone.utc).replace(tzinfo=None)
-    return Thing2Literal(value.strftime("%Y-%m-%d %H:%M:%S"), conv)
+    return Thing2Literal(value.strftime("%Y-%m-%d %H:%M:%S.%f"), conv)
 
 # MySQLdb-1.2.1 returns TIME columns as timedelta -- they are more like
 # timedelta in terms of actual behavior as they are signed and include days --
@@ -175,7 +175,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_forward_references = False
     # XXX MySQL DB-API drivers currently fail on binary data on Python 3.
     supports_binary_field = six.PY2
-    supports_microsecond_precision = False
     supports_regex_backreferencing = False
     supports_date_lookup_using_string = False
     can_introspect_binary_field = False
@@ -211,6 +210,10 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         return self._mysql_storage_engine != 'MyISAM'
 
     @cached_property
+    def supports_microsecond_precision(self):
+        return self.connection.mysql_version >= (5, 6, 4)
+
+    @cached_property
     def has_zoneinfo_database(self):
         # MySQL accepts full time zones names (eg. Africa/Nairobi) but rejects
         # abbreviations (eg. EAT). When pytz isn't installed and the current
diff --git a/django/db/backends/mysql/creation.py b/django/db/backends/mysql/creation.py
index fd3a595eb4..40d9251235 100644
--- a/django/db/backends/mysql/creation.py
+++ b/django/db/backends/mysql/creation.py
@@ -1,4 +1,5 @@
 from django.db.backends.creation import BaseDatabaseCreation
+from django.utils.functional import cached_property
 
 
 class DatabaseCreation(BaseDatabaseCreation):
@@ -6,7 +7,7 @@ class DatabaseCreation(BaseDatabaseCreation):
     # types, as strings. Column-type strings can contain format strings; they'll
     # be interpolated against the values of Field.__dict__ before being output.
     # If a column type is set to None, it won't be included in the output.
-    data_types = {
+    _data_types = {
         'AutoField': 'integer AUTO_INCREMENT',
         'BinaryField': 'longblob',
         'BooleanField': 'bool',
@@ -33,6 +34,13 @@ class DatabaseCreation(BaseDatabaseCreation):
         'UUIDField': 'char(32)',
     }
 
+    @cached_property
+    def data_types(self):
+        if self.connection.features.supports_microsecond_precision:
+            return dict(self._data_types, DateTimeField='datetime(6)', TimeField='time(6)')
+        else:
+            return self._data_types
+
     def sql_table_creation_suffix(self):
         suffix = []
         test_settings = self.connection.settings_dict['TEST']
diff --git a/docs/ref/databases.txt b/docs/ref/databases.txt
index cbc75d6a9c..63cb5f279e 100644
--- a/docs/ref/databases.txt
+++ b/docs/ref/databases.txt
@@ -496,11 +496,32 @@ for the field. This affects :class:`~django.db.models.CharField`,
 :class:`~django.db.models.SlugField` and
 :class:`~django.db.models.CommaSeparatedIntegerField`.
 
-DateTime fields
-~~~~~~~~~~~~~~~
+.. _mysql-fractional-seconds:
 
-MySQL does not store fractions of seconds. Fractions of seconds are truncated
-to zero when the time is stored.
+Fractional seconds support for Time and DateTime fields
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+MySQL 5.6.4 and later can store fractional seconds, provided that the
+column definition includes a fractional indication (e.g. ``DATETIME(6)``).
+Earlier versions do not support them at all.
+
+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 :class:`~django.db.migrations.operations.RunSQL` operation in a
+:ref:`data migration <data-migrations>`.
+
+.. versionchanged:: 1.8
+
+    Previously, Django truncated fractional seconds from ``datetime`` and
+    ``time`` values when using the MySQL backend. Now it lets the database
+    decide whether it should drop that part of the value or not. By default, new
+    ``DateTimeField`` or ``TimeField`` columns are now created with fractional
+    seconds support on MySQL 5.6.4 or later.
 
 ``TIMESTAMP`` columns
 ~~~~~~~~~~~~~~~~~~~~~
diff --git a/docs/releases/1.8.txt b/docs/releases/1.8.txt
index b37676008b..eef836f6aa 100644
--- a/docs/releases/1.8.txt
+++ b/docs/releases/1.8.txt
@@ -166,7 +166,9 @@ Database backends
 * The MySQL backend no longer strips microseconds from ``datetime`` values as
   MySQL 5.6.4 and up supports fractional seconds depending on the declaration
   of the datetime field (when ``DATETIME`` includes fractional precision greater
-  than 0).
+  than 0). New datetime database columns created with Django 1.8 and MySQL 5.6.4
+  and up will support microseconds. See the :ref:`MySQL database notes
+  <mysql-fractional-seconds>` for more details.
 
 Email
 ^^^^^