add translator between a predefined grammar and django's filter lookups

.travis.yml

@@ -24,14 +24,15 @@ install:
   - pip3 install "Django==${DJANGO_VERSION}"
   - pip3 install Sphinx
   - pip3 install flake8
-  - pip install coverage
-
+  - pip3 install coverage
+  - pip3 install lark-parser
 
 script:
   # makemigrations of each app is needed
   - python manage.py makemigrations drip
   - python manage.py makemigrations credits
   - python manage.py makemigrations auth
+  - python manage.py makemigrations grammar
   - python manage.py migrate
   - flake8 .
   - coverage run manage.py test

Pipfile

@@ -48,6 +48,7 @@ sphinx-rtd-theme = "*"
 [packages]
 Django = "==3.0.7"
 apscheduler = "*"
+lark-parser = "*"
 
 [requires]
 python_version = "3.8"

grammar/grammar.lark

@@ -0,0 +1,26 @@
+start       : query
+            | expression
+
+query       : "("* expression ")"*
+            | query CONNECTOR query
+
+expression  : computed OPERATOR atom
+
+computed    : FIELD
+            | computed "." computed
+
+atom        : "True" -> true
+            | "False" -> false
+            | NUMBER
+            | WORD
+            | ESCAPED_STRING -> string
+
+CONNECTOR   : "and" | "or"
+FIELD       : (WORD | "_")+
+OPERATOR    : "<" | "<=" | "==" | ">=" | ">" | "null" | "is"
+
+
+%import common.WORD
+%import common.NUMBER
+%import common.ESCAPED_STRING
+%ignore " "

grammar/parser.py

@@ -0,0 +1,55 @@
+from lark import Lark, Transformer
+
+
+class DjangoQueriesTransformer(Transformer):
+    """
+    Applies multiple transformations over the parsed tree
+    """
+    def start(self, tree):
+        return tree[0]
+
+    def OPERATOR(self, tree):
+        operator_map = {
+            ">": "__gt",
+            "<": "__lt",
+            "==": "__eq",
+            "is": "",
+            "null": "__isnull",
+        }
+        return operator_map[tree.value]
+
+    def atom(self, a):
+        (a,) = a
+        return a.value
+
+    def query(self, tree):
+        if len(tree) == 3:
+            return {**tree[0], **tree[2]}
+        else:
+            return tree[0]
+
+    def expression(self, tree):
+        return {"".join(tree[:2]): tree[2]}
+
+    def computed(self, tree):
+        return "__".join(tree)
+
+    def string(self, s):
+        (s,) = s
+        return s.strip('"')
+
+    def true(self, _):
+        return True
+
+    def false(self, _):
+        return False
+
+
+def translate_query(expression, grammar):
+    lexer = Lark(grammar)
+
+    parse_tree = lexer.parse(expression, start="start")
+    query_dict = DjangoQueriesTransformer(
+        visit_tokens=True
+    ).transform(parse_tree)
+    return query_dict

grammar/tests.py

@@ -0,0 +1,38 @@
+from pathlib import Path
+
+from django.test import TestCase
+from drip.models import Drip
+
+from .parser import translate_query
+
+
+class GrammarTest(TestCase):
+    def test_grammar(self):
+        grammar = Path(Path(__file__).parent, "grammar.lark").open()
+        grammar = "".join(grammar.readlines())
+
+        Drip(name="Nacho's Drip").save()
+        Drip(name="Nice Drip").save()
+        Drip(name="Not so nice").save()
+
+        input_expression = "(enabled is False)" \
+                           "and (sent_drips null True)" \
+                           "and (name is \"Nacho's Drip\")"
+        filter = translate_query(input_expression, grammar)
+        assert Drip.objects.filter(**filter).count() == 1
+
+        input_expression = "enabled is False"
+        filter = translate_query(input_expression, grammar)
+        assert Drip.objects.filter(**filter).count() == 3
+
+        input_expression = "(enabled is False) and (name is \"Not so nice\")"
+        filter = translate_query(input_expression, grammar)
+        assert Drip.objects.filter(**filter).count() == 1
+
+        input_expression = "(enabled is False) and (sent_drips null True)"
+        filter = translate_query(input_expression, grammar)
+        assert Drip.objects.filter(**filter).count() == 3
+
+        input_expression = "(enabled is False) and (sent_drips null False)"
+        filter = translate_query(input_expression, grammar)
+        assert Drip.objects.filter(**filter).count() == 0

setup.py

@@ -20,7 +20,7 @@
 author = 'Kalil de Lima'
 author_email = '[email protected]'
 license = 'MIT'
-install_requires = ['Django>=2.2', 'apscheduler']
+install_requires = ['Django>=2.2', 'apscheduler', 'lark-parser']
 keywords = 'django drip email user query'
 
 

testsettings.py

@@ -20,6 +20,7 @@
     'django.contrib.messages',
 
     'drip',
+    'grammar',
 
     # testing only
     'credits',