From b1c543d0910a79f4de93464fa684416c9441f7ce Mon Sep 17 00:00:00 2001
From: Adrian Holovaty <adrian@holovaty.com>
Date: Sun, 17 Jul 2005 20:16:06 +0000
Subject: [PATCH] Factored out database-specific date_trunc behavior into
 dbmod.get_date_trunc_sql(). Refs #46

git-svn-id: http://code.djangoproject.com/svn/django/trunk@161 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/core/db/__init__.py            |  1 +
 django/core/db/backends/mysql.py      | 13 +++++++++++++
 django/core/db/backends/postgresql.py |  6 ++++++
 django/core/meta.py                   | 10 +++++++---
 4 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/django/core/db/__init__.py b/django/core/db/__init__.py
index fc9dd75f61..17e3d2a7fd 100644
--- a/django/core/db/__init__.py
+++ b/django/core/db/__init__.py
@@ -29,5 +29,6 @@ dictfetchall = dbmod.dictfetchall
 dictfetchall = dbmod.dictfetchall
 get_last_insert_id = dbmod.get_last_insert_id
 get_date_extract_sql = dbmod.get_date_extract_sql
+get_date_trunc_sql = dbmod.get_date_trunc_sql
 OPERATOR_MAPPING = dbmod.OPERATOR_MAPPING
 DATA_TYPES = dbmod.DATA_TYPES
diff --git a/django/core/db/backends/mysql.py b/django/core/db/backends/mysql.py
index 001a32c191..e3e3a5a299 100644
--- a/django/core/db/backends/mysql.py
+++ b/django/core/db/backends/mysql.py
@@ -64,8 +64,21 @@ def get_last_insert_id(cursor, table_name, pk_name):
 
 def get_date_extract_sql(lookup_type, table_name):
     # lookup_type is 'year', 'month', 'day'
+    # http://dev.mysql.com/doc/mysql/en/date-and-time-functions.html
     return "EXTRACT(%s FROM %s)" % (lookup_type.upper(), table_name)
 
+def get_date_trunc_sql(lookup_type, field_name):
+    # lookup_type is 'year', 'month', 'day'
+    # http://dev.mysql.com/doc/mysql/en/date-and-time-functions.html
+    # MySQL doesn't support DATE_TRUNC, so we fake it by subtracting intervals.
+    # If you know of a better way to do this, please file a Django ticket.
+    subtractions = ["interval (DATE_FORMAT(%s, '%%%%s')) second - interval (DATE_FORMAT(%s, '%%%%i')) minute - interval (DATE_FORMAT(%s, '%%%%H')) hour" % (field_name, field_name, field_name)]
+    if lookup_type in ('year', 'month'):
+        subtractions.append(" - interval (DATE_FORMAT(%s, '%%%%e')-1) day" % field_name)
+    if lookup_type == 'year':
+        subtractions.append(" - interval (DATE_FORMAT(%s, '%%%%m')-1) month" % field_name)
+    return "(%s - %s)" % (field_name, ''.join(subtractions))
+
 OPERATOR_MAPPING = {
     'exact': '=',
     'iexact': 'LIKE',
diff --git a/django/core/db/backends/postgresql.py b/django/core/db/backends/postgresql.py
index df7829f683..8a629453b3 100644
--- a/django/core/db/backends/postgresql.py
+++ b/django/core/db/backends/postgresql.py
@@ -63,8 +63,14 @@ def get_last_insert_id(cursor, table_name, pk_name):
 
 def get_date_extract_sql(lookup_type, table_name):
     # lookup_type is 'year', 'month', 'day'
+    # http://www.postgresql.org/docs/8.0/static/functions-datetime.html#FUNCTIONS-DATETIME-EXTRACT
     return "EXTRACT('%s' FROM %s)" % (lookup_type, table_name)
 
+def get_date_trunc_sql(lookup_type, field_name):
+    # lookup_type is 'year', 'month', 'day'
+    # http://www.postgresql.org/docs/8.0/static/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC
+    return "DATE_TRUNC('%s', %s)" % (lookup_type, field_name)
+
 # Register these custom typecasts, because Django expects dates/times to be
 # in Python's native (standard-library) datetime/time format, whereas psycopg
 # use mx.DateTime by default.
diff --git a/django/core/meta.py b/django/core/meta.py
index 8e7c22596e..a144cde8bd 100644
--- a/django/core/meta.py
+++ b/django/core/meta.py
@@ -1264,6 +1264,7 @@ def function_get_latest(opts, klass, does_not_exist_exception, **kwargs):
     return function_get_object(opts, klass, does_not_exist_exception, **kwargs)
 
 def function_get_date_list(opts, field, *args, **kwargs):
+    from django.core.db.typecasts import typecast_timestamp
     kind = args and args[0] or kwargs['kind']
     assert kind in ("month", "year", "day"), "'kind' must be one of 'year', 'month' or 'day'."
     order = 'ASC'
@@ -1275,10 +1276,13 @@ def function_get_date_list(opts, field, *args, **kwargs):
     if field.null:
         kwargs.setdefault('where', []).append('%s.%s IS NOT NULL' % (opts.db_table, field.name))
     select, sql, params = function_get_sql_clause(opts, **kwargs)
-    sql = "SELECT DATE_TRUNC(%%s, %s.%s) %s GROUP BY 1 ORDER BY 1 %s" % (opts.db_table, field.name, sql, order)
+    sql = 'SELECT %s %s GROUP BY 1 ORDER BY 1' % (db.get_date_trunc_sql(kind, '%s.%s' % (opts.db_table, field.name)), sql)
     cursor = db.db.cursor()
-    cursor.execute(sql, [kind] + params)
-    return [row[0] for row in cursor.fetchall()]
+    cursor.execute(sql, params)
+    # We have to manually run typecast_timestamp(str()) on the results, because
+    # MySQL doesn't automatically cast the result of date functions as datetime
+    # objects -- MySQL returns the values as strings, instead.
+    return [typecast_timestamp(str(row[0])) for row in cursor.fetchall()]
 
 ###################################
 # HELPER FUNCTIONS (MANIPULATORS) #