Reconciling where- and having-clause behaviour.

Extricated the code that works directly with SQL columns (standard
"where" stuff) from the the code that takes SQL fragments and combines
it with lookup types and values. The latter portion is now more
generally reusable. Any existing code that was poking at Query.having
will now break in very visible ways (no subtle miscalculations, which is
a good thing).

This patch, en passant, removes the existing "having" test, since the
new implementation requires more setting up than previously. The
aggregates support (currently in a separate codebase) has tests for this
functionality that work as a replacement for the removed test.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9700 bcc190cf-cafb-0310-a4f2-bffc1f526a37

3 files changed, 101 insertions, 64 deletions

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 8c5ef3355e..61c1e51557 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -16,7 +16,7 @@ from django.db import connection
 from django.db.models import signals
 from django.db.models.fields import FieldDoesNotExist
 from django.db.models.query_utils import select_related_descend
-from django.db.models.sql.where import WhereNode, EverythingNode, AND, OR
+from django.db.models.sql.where import WhereNode, Constraint, EverythingNode, AND, OR
 from django.db.models.sql.datastructures import Count
 from django.core.exceptions import FieldError
 from datastructures import EmptyResultSet, Empty, MultiJoin
@@ -66,7 +66,7 @@ class BaseQuery(object):
         self.where = where()
         self.where_class = where
         self.group_by = []
-        self.having = []
+        self.having = where()
         self.order_by = []
         self.low_mark, self.high_mark = 0, None  # Used for offset/limit
         self.distinct = False
@@ -172,7 +172,7 @@ class BaseQuery(object):
         obj.where = deepcopy(self.where)
         obj.where_class = self.where_class
         obj.group_by = self.group_by[:]
-        obj.having = self.having[:]
+        obj.having = deepcopy(self.having)
         obj.order_by = self.order_by[:]
         obj.low_mark, obj.high_mark = self.low_mark, self.high_mark
         obj.distinct = self.distinct
@@ -261,7 +261,9 @@ class BaseQuery(object):
         # get_from_clause() for details.
         from_, f_params = self.get_from_clause()
 
-        where, w_params = self.where.as_sql(qn=self.quote_name_unless_alias)
+        qn = self.quote_name_unless_alias
+        where, w_params = self.where.as_sql(qn=qn)
+        having, h_params = self.having.as_sql(qn=qn)
         params = []
         for val in self.extra_select.itervalues():
             params.extend(val[1])
@@ -291,9 +293,8 @@ class BaseQuery(object):
             if not ordering:
                 ordering = self.connection.ops.force_no_ordering()
 
-        if self.having:
-            having, h_params = self.get_having()
-            result.append('HAVING %s' % ', '.join(having))
+        if having:
+            result.append('HAVING %s' % having)
             params.extend(h_params)
 
         if ordering:
@@ -577,24 +578,6 @@ class BaseQuery(object):
                 result.append(str(col))
         return result
 
-    def get_having(self):
-        """
-        Returns a tuple representing the SQL elements in the "having" clause.
-        By default, the elements of self.having have their as_sql() method
-        called or are returned unchanged (if they don't have an as_sql()
-        method).
-        """
-        result = []
-        params = []
-        for elt in self.having:
-            if hasattr(elt, 'as_sql'):
-                sql, params = elt.as_sql()
-                result.append(sql)
-                params.extend(params)
-            else:
-                result.append(elt)
-        return result, params
-
     def get_ordering(self):
         """
         Returns list representing the SQL elements in the "order by" clause.
@@ -1197,7 +1180,8 @@ class BaseQuery(object):
             self.promote_alias_chain(join_it, join_promote)
             self.promote_alias_chain(table_it, table_promote)
 
-        self.where.add((alias, col, field, lookup_type, value), connector)
+        self.where.add((Constraint(alias, col, field), lookup_type, value),
+            connector)
 
         if negate:
             self.promote_alias_chain(join_list)
@@ -1207,7 +1191,7 @@ class BaseQuery(object):
                         if self.alias_map[alias][JOIN_TYPE] == self.LOUTER:
                             j_col = self.alias_map[alias][RHS_JOIN_COL]
                             entry = self.where_class()
-                            entry.add((alias, j_col, None, 'isnull', True), AND)
+                            entry.add((Constraint(alias, j_col, None), 'isnull', True), AND)
                             entry.negate()
                             self.where.add(entry, AND)
                             break
@@ -1216,7 +1200,7 @@ class BaseQuery(object):
                     # exclude the "foo__in=[]" case from this handling, because
                     # it's short-circuited in the Where class.
                     entry = self.where_class()
-                    entry.add((alias, col, None, 'isnull', True), AND)
+                    entry.add((Constraint(alias, col, None), 'isnull', True), AND)
                     entry.negate()
                     self.where.add(entry, AND)
 
diff --git a/django/db/models/sql/subqueries.py b/django/db/models/sql/subqueries.py
index 39ef439dc9..524b0894c5 100644
--- a/django/db/models/sql/subqueries.py
+++ b/django/db/models/sql/subqueries.py
@@ -6,7 +6,7 @@ from django.core.exceptions import FieldError
 from django.db.models.sql.constants import *
 from django.db.models.sql.datastructures import Date
 from django.db.models.sql.query import Query
-from django.db.models.sql.where import AND
+from django.db.models.sql.where import AND, Constraint
 
 __all__ = ['DeleteQuery', 'UpdateQuery', 'InsertQuery', 'DateQuery',
         'CountQuery']
@@ -48,8 +48,9 @@ class DeleteQuery(Query):
             if not isinstance(related.field, generic.GenericRelation):
                 for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
                     where = self.where_class()
-                    where.add((None, related.field.m2m_reverse_name(),
-                            related.field, 'in',
+                    where.add((Constraint(None,
+                            related.field.m2m_reverse_name(), related.field),
+                            'in',
                             pk_list[offset : offset+GET_ITERATOR_CHUNK_SIZE]),
                             AND)
                     self.do_query(related.field.m2m_db_table(), where)
@@ -59,11 +60,11 @@ class DeleteQuery(Query):
             if isinstance(f, generic.GenericRelation):
                 from django.contrib.contenttypes.models import ContentType
                 field = f.rel.to._meta.get_field(f.content_type_field_name)
-                w1.add((None, field.column, field, 'exact',
+                w1.add((Constraint(None, field.column, field), 'exact',
                         ContentType.objects.get_for_model(cls).id), AND)
             for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
                 where = self.where_class()
-                where.add((None, f.m2m_column_name(), f, 'in',
+                where.add((Constraint(None, f.m2m_column_name(), f), 'in',
                         pk_list[offset : offset + GET_ITERATOR_CHUNK_SIZE]),
                         AND)
                 if w1:
@@ -81,7 +82,7 @@ class DeleteQuery(Query):
         for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
             where = self.where_class()
             field = self.model._meta.pk
-            where.add((None, field.column, field, 'in',
+            where.add((Constraint(None, field.column, field), 'in',
                     pk_list[offset : offset + GET_ITERATOR_CHUNK_SIZE]), AND)
             self.do_query(self.model._meta.db_table, where)
 
@@ -212,7 +213,7 @@ class UpdateQuery(Query):
         for offset in range(0, len(pk_list), GET_ITERATOR_CHUNK_SIZE):
             self.where = self.where_class()
             f = self.model._meta.pk
-            self.where.add((None, f.column, f, 'in',
+            self.where.add((Constraint(None, f.column, f), 'in',
                     pk_list[offset : offset + GET_ITERATOR_CHUNK_SIZE]),
                     AND)
             self.values = [(related_field.column, None, '%s')]
diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index 662d99a4a2..a9fca7df11 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -13,6 +13,13 @@ from datastructures import EmptyResultSet, FullResultSet
 AND = 'AND'
 OR = 'OR'
 
+class EmptyShortCircuit(Exception):
+    """
+    Internal exception used to indicate that a "matches nothing" node should be
+    added to the where-clause.
+    """
+    pass
+
 class WhereNode(tree.Node):
     """
     Used to represent the SQL where-clause.
@@ -35,36 +42,35 @@ class WhereNode(tree.Node):
         storing any reference to field objects). Otherwise, the 'data' is
         stored unchanged and can be anything with an 'as_sql()' method.
         """
-        # Because of circular imports, we need to import this here.
-        from django.db.models.base import ObjectDoesNotExist
-
         if not isinstance(data, (list, tuple)):
             super(WhereNode, self).add(data, connector)
             return
 
-        alias, col, field, lookup_type, value = data
-        try:
-            if field:
-                params = field.get_db_prep_lookup(lookup_type, value)
-                db_type = field.db_type()
-            else:
-                # This is possible when we add a comparison to NULL sometimes
-                # (we don't really need to waste time looking up the associated
-                # field object).
-                params = Field().get_db_prep_lookup(lookup_type, value)
-                db_type = None
-        except ObjectDoesNotExist:
-            # This can happen when trying to insert a reference to a null pk.
-            # We break out of the normal path and indicate there's nothing to
-            # match.
-            super(WhereNode, self).add(NothingNode(), connector)
-            return
+        obj, lookup_type, value = data
+        if hasattr(obj, "process"):
+            try:
+                obj, params = obj.process(lookup_type, value)
+            except EmptyShortCircuit:
+                # There are situations where we want to short-circuit any
+                # comparisons and make sure that nothing is returned. One
+                # example is when checking for a NULL pk value, or the
+                # equivalent.
+                super(WhereNode, self).add(NothingNode(), connector)
+                return
+        else:
+            params = Field().get_db_prep_lookup(lookup_type, value)
+
+        # The "annotation" parameter is used to pass auxilliary information
+        # about the value(s) to the query construction. Specifically, datetime
+        # and empty values need special handling. Other types could be used
+        # here in the future (using Python types is suggested for consistency).
         if isinstance(value, datetime.datetime):
             annotation = datetime.datetime
         else:
             annotation = bool(value)
-        super(WhereNode, self).add((alias, col, db_type, lookup_type,
-                annotation, params), connector)
+
+        super(WhereNode, self).add((obj, lookup_type, annotation, params),
+                connector)
 
     def as_sql(self, qn=None):
         """
@@ -130,12 +136,13 @@ class WhereNode(tree.Node):
         Returns the string for the SQL fragment and the parameters to use for
         it.
         """
-        table_alias, name, db_type, lookup_type, value_annot, params = child
-        if table_alias:
-            lhs = '%s.%s' % (qn(table_alias), qn(name))
+        lvalue, lookup_type, value_annot, params = child
+        if isinstance(lvalue, tuple):
+            # A direct database column lookup.
+            field_sql = self.sql_for_columns(lvalue, qn)
         else:
-            lhs = qn(name)
-        field_sql = connection.ops.field_cast_sql(db_type) % lhs
+            # A smart object with an as_sql() method.
+            field_sql = lvalue.as_sql(quote_func=qn)
 
         if value_annot is datetime.datetime:
             cast_sql = connection.ops.datetime_cast_sql()
@@ -175,6 +182,19 @@ class WhereNode(tree.Node):
 
         raise TypeError('Invalid lookup_type: %r' % lookup_type)
 
+    def sql_for_columns(self, data, qn):
+        """
+        Returns the SQL fragment used for the left-hand side of a column
+        constraint (for example, the "T1.foo" portion in the clause
+        "WHERE ... T1.foo = 6").
+        """
+        table_alias, name, db_type = data
+        if table_alias:
+            lhs = '%s.%s' % (qn(table_alias), qn(name))
+        else:
+            lhs = qn(name)
+        return connection.ops.field_cast_sql(db_type) % lhs
+
     def relabel_aliases(self, change_map, node=None):
         """
         Relabels the alias values of any children. 'change_map' is a dictionary
@@ -188,8 +208,10 @@ class WhereNode(tree.Node):
             elif isinstance(child, tree.Node):
                 self.relabel_aliases(change_map, child)
             else:
-                if child[0] in change_map:
-                    node.children[pos] = (change_map[child[0]],) + child[1:]
+                elt = list(child[0])
+                if elt[0] in change_map:
+                    elt[0] = change_map[elt[0]]
+                    node.children[pos] = (tuple(elt),) + child[1:]
 
 class EverythingNode(object):
     """
@@ -211,3 +233,33 @@ class NothingNode(object):
     def relabel_aliases(self, change_map, node=None):
         return
 
+class Constraint(object):
+    """
+    An object that can be passed to WhereNode.add() and knows how to
+    pre-process itself prior to including in the WhereNode.
+    """
+    def __init__(self, alias, col, field):
+        self.alias, self.col, self.field = alias, col, field
+
+    def process(self, lookup_type, value):
+        """
+        Returns a tuple of data suitable for inclusion in a WhereNode
+        instance.
+        """
+        # Because of circular imports, we need to import this here.
+        from django.db.models.base import ObjectDoesNotExist
+        try:
+            if self.field:
+                params = self.field.get_db_prep_lookup(lookup_type, value)
+                db_type = self.field.db_type()
+            else:
+                # This branch is used at times when we add a comparison to NULL
+                # (we don't really want to waste time looking up the associated
+                # field object at the calling location).
+                params = Field().get_db_prep_lookup(lookup_type, value)
+                db_type = None
+        except ObjectDoesNotExist:
+            raise EmptyShortCircuit
+
+        return (self.alias, self.col, db_type), params
+