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

1 files changed, 81 insertions, 29 deletions

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
+