Merge pull request #16 from geopython/optimize

Optimization backend

Author: constantinius

README.md

@@ -341,3 +341,37 @@ layer = data.ExecuteSQL(f"""
 Note that it is vital to specify the `SQLite` dialect as this is the one used internally.
 
 :warning: Input values are *not* sanitized/separated from the generated SQL text. This is due to the compatibility with the OGR API not allowing to separate the SQL from the arguments.
+
+
+### Optimization
+
+This is a special kind of backend, as the result of the AST evaluation is actually a new AST. The purpose of this backend is to eliminate static branches of the AST, potentially reducing the cost of an actual evaluation for filtering values.
+
+What parts of an AST can be optimized:
+
+- Arithmetic operations of purely static operands
+- All predicates (spatial, temporal, array, `like`, `between`, `in`) if all of the operands are already static
+- Functions, when passed in a special lookup table and all arguments are static
+- `And` and `Or` combinators can be eliminated if either branch can be predicted
+
+What cannot be optimized are branches that contain references to attributes or functions not passed in the dictionary.
+
+The following example shows how a static computation can be optimized to a static value, replacing the whole branch of the AST:
+
+```python
+>>> import math
+>>> from pygeofilter import ast
+>>> from pygeofilter.parsers.ecql import parse
+>>> from pygeofilter.backends.optimize import optimize
+>>>
+>>> root = parse('attr < sin(3.7) - 5')
+>>> optimized_root = optimize(root, {'sin': math.sin})
+>>> print(ast.get_repr(root))
+ATTRIBUTE attr < (
+    (
+            sin (3.7)
+    ) - 5
+)
+>>> print(ast.get_repr(optimized_root))
+ATTRIBUTE attr < -5.529836140908493
+```

pygeofilter/ast.py

@@ -157,7 +157,7 @@ def get_sub_nodes(self):
         return [self.lhs, self.rhs]
 
     def get_template(self):
-        return f"{{}} {self.op} {{}}"
+        return f"{{}} {self.op.value} {{}}"
 
 
 @dataclass

pygeofilter/backends/django/evaluate.py

@@ -170,6 +170,10 @@ def arithmetic(self, node, lhs, rhs):
     def literal(self, node):
         return filters.literal(node)
 
+    @handle(values.Interval)
+    def interval(self, node):
+        return filters.literal((node.start, node.end))
+
     @handle(values.Geometry)
     def geometry(self, node):
         return GEOSGeometry(json.dumps(node.__geo_interface__))

pygeofilter/backends/evaluator.py

@@ -1,3 +1,30 @@
+# ------------------------------------------------------------------------------
+#
+# Project: pygeofilter <https://github.com/geopython/pygeofilter>
+# Authors: Fabian Schindler <[email protected]>
+#
+# ------------------------------------------------------------------------------
+# Copyright (C) 2021 EOX IT Services GmbH
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies of this Software or works derived from this Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+# ------------------------------------------------------------------------------
+
 from functools import wraps
 from typing import Any, Callable, List, Type
 

pygeofilter/backends/geopandas/evaluate.py

@@ -145,6 +145,10 @@ def function(self, node, *arguments):
     def literal(self, node):
         return node
 
+    @handle(values.Interval)
+    def interval(self, node):
+        return (node.start, node.end)
+
     @handle(values.Geometry)
     def geometry(self, node):
         return geometry.shape(node)

pygeofilter/backends/native/evaluate.py

@@ -184,6 +184,10 @@ def function(self, node, *arguments):
     def literal(self, node):
         return node
 
+    @handle(values.Interval)
+    def interval(self, node):
+        return node
+
     @handle(values.Geometry)
     def geometry(self, node):
         return shapely.geometry.shape(node)
@@ -198,8 +202,9 @@ def envelope(self, node):
 def to_interval(value):
     # TODO:
     zulu = None
-    if isinstance(value, (list, tuple)):
-        low, high = value
+    if isinstance(value, values.Interval):
+        low = value.start
+        high = value.end
         if isinstance(low, date):
             low = datetime.combine(low, time.min, zulu)
         if isinstance(high, date):