Use SQL statement for summing up weights

* Update models: Bill.pay_each()
* Import sql func
* reformatted using black
* Added ModelsTestCase.test_bill_pay_each() in order to test the SQL query change within pay_each.
Had to add Project.ProjectQuery.get_by_name() for the test.

ihatemoney/models.py

@@ -6,6 +6,7 @@ from flask import g, current_app
 
 from debts import settle
 from sqlalchemy import orm
+from sqlalchemy.sql import func
 from itsdangerous import (
     TimedJSONWebSignatureSerializer,
     URLSafeSerializer,
@@ -17,6 +18,9 @@ db = SQLAlchemy()
 
 
 class Project(db.Model):
+    class ProjectQuery(BaseQuery):
+        def get_by_name(self, name):
+            return Project.query.filter(Project.name == name).one()
 
     id = db.Column(db.String(64), primary_key=True)
 
@@ -25,6 +29,8 @@ class Project(db.Model):
     contact_email = db.Column(db.String(128))
     members = db.relationship("Person", backref="project")
 
+    query_class = ProjectQuery
+
     @property
     def _to_serialize(self):
         obj = {
@@ -388,8 +394,11 @@ class Bill(db.Model):
     def pay_each(self):
         """Compute what each share has to pay"""
         if self.owers:
-            # FIXME: SQL might do that more efficiently
-            weights = sum(i.weight for i in self.owers)
+            weights = (
+                db.session.query(func.sum(Person.weight))
+                .join(billowers, Bill)
+                .filter(Bill.id == self.id)
+            ).scalar()
             return self.amount / weights
         else:
             return 0

ihatemoney/tests/tests.py

@@ -19,6 +19,7 @@ from ihatemoney.run import create_app, db, load_configuration
 from ihatemoney.manage import GenerateConfig, GeneratePasswordHash, DeleteProject
 from ihatemoney import models
 from ihatemoney import utils
+from sqlalchemy import orm
 
 # Unset configuration file env var if previously set
 os.environ.pop("IHATEMONEY_SETTINGS_FILE_PATH", None)
@@ -2140,5 +2141,68 @@ class CommandTestCase(BaseTestCase):
         self.assertEqual(len(models.Project.query.all()), 0)
 
 
+class ModelsTestCase(IhatemoneyTestCase):
+    def test_bill_pay_each(self):
+
+        self.post_project("raclette")
+
+        # add members
+        self.client.post("/raclette/members/add", data={"name": "alexis", "weight": 2})
+        self.client.post("/raclette/members/add", data={"name": "fred"})
+        self.client.post("/raclette/members/add", data={"name": "tata"})
+        # Add a member with a balance=0 :
+        self.client.post("/raclette/members/add", data={"name": "toto"})
+
+        # create bills
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2011-08-10",
+                "what": "fromage à raclette",
+                "payer": 1,
+                "payed_for": [1, 2, 3],
+                "amount": "10.0",
+            },
+        )
+
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2011-08-10",
+                "what": "red wine",
+                "payer": 2,
+                "payed_for": [1],
+                "amount": "20",
+            },
+        )
+
+        self.client.post(
+            "/raclette/add",
+            data={
+                "date": "2011-08-10",
+                "what": "delicatessen",
+                "payer": 1,
+                "payed_for": [1, 2],
+                "amount": "10",
+            },
+        )
+
+        project = models.Project.query.get_by_name(name="raclette")
+        alexis = models.Person.query.get_by_name(name="alexis", project=project)
+        alexis_bills = models.Bill.query.options(
+            orm.subqueryload(models.Bill.owers)
+        ).filter(models.Bill.owers.contains(alexis))
+        for bill in alexis_bills.all():
+            if bill.what == "red wine":
+                pay_each_expected = 20 / 2
+                self.assertEqual(bill.pay_each(), pay_each_expected)
+            if bill.what == "fromage à raclette":
+                pay_each_expected = 10 / 4
+                self.assertEqual(bill.pay_each(), pay_each_expected)
+            if bill.what == "delicatessen":
+                pay_each_expected = 10 / 3
+                self.assertEqual(bill.pay_each(), pay_each_expected)
+
+
 if __name__ == "__main__":
     unittest.main()