Preliminary implementation for the evaluation framework

1 files changed, 96 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/evaluator.py b/lib/sqlalchemy/orm/evaluator.py
new file mode 100644
index 000000000..c4517e494
--- /dev/null
+++ b/lib/sqlalchemy/orm/evaluator.py
@@ -0,0 +1,96 @@
+from sqlalchemy.sql import operators, functions
+from sqlalchemy.sql import expression as sql
+from sqlalchemy.util import Set
+import operator
+
+class UnevaluatableError(Exception):
+    pass
+
+_straight_ops = Set([getattr(operators, op) for op in [
+    'add', 'mul', 'sub', 'div', 'mod', 'truediv', 'lt', 'le', 'ne', 'gt', 'ge', 'eq'
+]])
+
+
+_notimplemented_ops = Set([getattr(operators, op) for op in [
+    'like_op', 'notlike_op', 'ilike_op', 'notilike_op', 'between_op', 'in_op', 'notin_op',
+    'endswith_op', 'concat_op',
+]])
+
+class EvaluatorCompiler(object):
+    def process(self, clause):
+        meth = getattr(self, "visit_%s" % clause.__visit_name__, None)
+        if not meth:
+            raise UnevaluatableError("Cannot evaluate %s" % type(clause).__name__)
+        return meth(clause)
+    
+    def visit_grouping(self, clause):
+        return self.process(clause.element)
+    
+    def visit_null(self, clause):
+        return lambda obj: None
+    
+    def visit_column(self, clause):
+        if 'parententity' in clause._annotations:
+            key = clause._annotations['parententity']._get_col_to_prop(clause).key
+        else:
+            key = clause.key
+        get_corresponding_attr = operator.attrgetter(key)
+        return lambda obj: get_corresponding_attr(obj)
+    
+    def visit_clauselist(self, clause):
+        evaluators = map(self.process, clause.clauses)
+        if clause.operator is operators.or_:
+            def evaluate(obj):
+                has_null = False
+                for sub_evaluate in evaluators:
+                    value = sub_evaluate(obj)
+                    if value:
+                        return True
+                    has_null = has_null or value is None
+                if has_null:
+                    return None
+                return False
+        if clause.operator is operators.and_:
+            def evaluate(obj):
+                for sub_evaluate in evaluators:
+                    value = sub_evaluate(obj)
+                    if not value:
+                        if value is None:
+                            return None
+                        return False
+                return True
+        
+        return evaluate
+
+    def visit_binary(self, clause):
+        eval_left,eval_right = map(self.process, [clause.left, clause.right])
+        operator = clause.operator
+        if operator is operators.is_:
+            def evaluate(obj):
+                return eval_left(obj) == eval_right(obj)
+        if operator is operators.isnot:
+            def evaluate(obj):
+                return eval_left(obj) != eval_right(obj)
+        elif operator in _straight_ops:
+            def evaluate(obj):
+                left_val = eval_left(obj)
+                right_val = eval_right(obj)
+                if left_val is None or right_val is None:
+                    return None
+                return operator(eval_left(obj), eval_right(obj))
+        return evaluate
+
+    def visit_unary(self, clause):
+        eval_inner = self.process(clause.element)
+        if clause.operator is operators.inv:
+            def evaluate(obj):
+                value = eval_inner(obj)
+                if value is None:
+                    return None
+                return not value
+            return evaluate
+        raise UnevaluatableError("Cannot evaluate %s with operator %s" % (type(clause).__name__, clause.operator))
+    
+    def visit_bindparam(self, clause):
+        val = clause.value
+        return lambda obj: val