[Performance] Get weight sum along with bills to scale (#949)

* get weight sum along with bills to scale

otherwise, we need to get the weight sum for each displayed bill.
Here, we are much more scalable

* add test

* format

* remove unused import

* oops, restore pagination to 100

* add comments

* format

* rename method to make it clearer

And also, make it static, since it doesn't rely on instance.

* improve comments and naming

* improve naming

* missing article

ihatemoney/models.py

@@ -250,13 +250,37 @@ class Project(db.Model):
 
     def get_bills(self):
         """Return the list of bills related to this project"""
+        return self.order_bills(self.get_bills_unordered())
+
+    @staticmethod
+    def order_bills(query):
         return (
-            self.get_bills_unordered()
-            .order_by(Bill.date.desc())
+            query.order_by(Bill.date.desc())
             .order_by(Bill.creation_date.desc())
             .order_by(Bill.id.desc())
         )
 
+    def get_bill_weights(self):
+        """
+        Return all bills for this project, along with the sum of weight for each bill.
+        Each line is a (float, Bill) tuple.
+
+        Result is unordered.
+        """
+        return (
+            db.session.query(func.sum(Person.weight), Bill)
+            .options(orm.subqueryload(Bill.owers))
+            .select_from(Person)
+            .join(billowers, Bill, Project)
+            .filter(Person.project_id == Project.id)
+            .filter(Project.id == self.id)
+            .group_by(Bill.id)
+        )
+
+    def get_bill_weights_ordered(self):
+        """Ordered version of get_bill_weights"""
+        return self.order_bills(self.get_bill_weights())
+
     def get_member_bills(self, member_id):
         """Return the list of bills related to a specific member"""
         return (

ihatemoney/templates/list_bills.html

@@ -1,7 +1,7 @@
 {% extends "sidebar_table_layout.html" %}
 
-{%- macro bill_amount(bill, currency=bill.original_currency, amount=bill.amount) %}
-    {{ amount|currency(currency) }} ({{ _("%(amount)s each", amount=bill.pay_each_default(amount)|currency(currency)) }})
+{%- macro weighted_bill_amount(bill, weights, currency=bill.original_currency, amount=bill.amount) %}
+    {{ amount|currency(currency) }} ({{ _("%(amount)s each", amount=(amount / weights)|currency(currency)) }})
 {% endmacro -%}
 
 {% block title %} - {{ g.project.name }}{% endblock %}
@@ -109,7 +109,7 @@
                 </th><th>{{ _("Actions") }}</th></tr>
             </thead>
         <tbody>
-        {% for bill in bills.items %}
+        {% for (weights, bill) in bills.items %}
         <tr owers="{{bill.owers|join(',','id')}}" payer="{{bill.payer.id}}">
                 <td>
                     <span data-toggle="tooltip" data-placement="top"
@@ -128,8 +128,8 @@
                 {%- endif %}</td>
                 <td>
                     <span data-toggle="tooltip" data-placement="top"
-                        title="{{ bill_amount(bill, g.project.default_currency, bill.converted_amount) if bill.original_currency != g.project.default_currency else '' }}">
-                        {{ bill_amount(bill) }}
+                        title="{{ weighted_bill_amount(bill, weights, g.project.default_currency, bill.converted_amount) if bill.original_currency != g.project.default_currency else '' }}">
+                        {{ weighted_bill_amount(bill, weights) }}
                     </span>
                 </td>
                 <td class="bill-actions">

ihatemoney/tests/main_test.py

@@ -108,6 +108,62 @@ class CommandTestCase(BaseTestCase):
 
 
 class ModelsTestCase(IhatemoneyTestCase):
+    def test_weighted_bills(self):
+        """Test the SQL request that fetch all bills and weights"""
+        self.post_project("raclette")
+
+        # add members
+        self.client.post("/raclette/members/add", data={"name": "zorglub", "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": "pépé"})
+
+        # 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")
+        for (weight, bill) in project.get_bill_weights().all():
+            if bill.what == "red wine":
+                pay_each_expected = 20 / 2
+                self.assertEqual(bill.amount / weight, pay_each_expected)
+            if bill.what == "fromage à raclette":
+                pay_each_expected = 10 / 4
+                self.assertEqual(bill.amount / weight, pay_each_expected)
+            if bill.what == "delicatessen":
+                pay_each_expected = 10 / 3
+                self.assertEqual(bill.amount / weight, pay_each_expected)
+
     def test_bill_pay_each(self):
 
         self.post_project("raclette")

ihatemoney/web.py

@@ -28,7 +28,6 @@ from flask import (
 )
 from flask_babel import gettext as _
 from flask_mail import Message
-from sqlalchemy import orm
 from sqlalchemy_continuum import Operation
 from werkzeug.exceptions import NotFound
 from werkzeug.security import check_password_hash, generate_password_hash
@@ -609,16 +608,17 @@ def list_bills():
     # set the last selected payer as default choice if exists
     if "last_selected_payer" in session:
         bill_form.payer.data = session["last_selected_payer"]
-    # Preload the "owers" relationship for all bills
-    bills = (
-        g.project.get_bills()
-        .options(orm.subqueryload(Bill.owers))
-        .paginate(per_page=100, error_out=True)
+
+    # Each item will be a (weight_sum, Bill) tuple.
+    # TODO: improve this awkward result using column_property:
+    # https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html.
+    weighted_bills = g.project.get_bill_weights_ordered().paginate(
+        per_page=100, error_out=True
     )
 
     return render_template(
         "list_bills.html",
-        bills=bills,
+        bills=weighted_bills,
         member_form=MemberForm(g.project),
         bill_form=bill_form,
         csrf_form=csrf_form,