Django Rest join models on multiple fields - django

Question

I have two models as below.
These models store budget sales data and actual sales data for each project by each month.
# To test join on multiple keys
class ActualSales(models.Model):
time_id = models.CharField(max_length=8)
project = models.CharField(max_length=100)
actual_sales = models.DecimalField(max_digits=20, decimal_places=3)
adjustment = models.DecimalField(max_digits=20, decimal_places=3)
class BudgetSales(models.Model):
time_id = models.CharField(max_length=8)
project = models.CharField(max_length=100)
budget_sales = models.DecimalField(max_digits=20, decimal_places=3)
And the data will somewhat looks like this.
Model A
| time_id | project | sales | adjustment |
+---------+-----------+-------+------------+
| 2019JAN | Project A | 1000 | 10 |
| 2019JAN | Project B | 2500 | 5 |
| 2019FEB | Project A | 1100 | 0 |
| 2019FEB | Project B | 2400 | -10 |
+---------+-----------+-------+------------+
Model B
| time_id | project | budget |
+---------+-----------+--------+
| 2019JAN | Project A | 1100 |
| 2019JAN | Project B | 2400 |
| 2019FEB | Project A | 1000 |
| 2019FEB | Project B | 2500 |
+---------+-----------+--------+
And I'm looking to produce an array of objects with each object represent each project's result each month, similarly to the way we join 2 tables with sql. However, I'm unsure how to write the serialiser and API Viewset for this.
[
{
time_id: "2019JAN",
project: "Project A",
sales: "1000",
adjustment: "10",
budget: "1100"
},
{
time_id: "2019JAN",
project: "Project B",
sales: "2500",
adjustment: "5",
budget: "2400"
},
{
time_id: "2019FEB",
project: "Project A",
sales: "1100",
adjustment: "0",
budget: "1000"
},
{
time_id: "2019FEB",
project: "Project B",
sales: "2400",
adjustment: "-10",
budget: "2500"
}
]

Answer 1

You can try this
Models.py
class ActualSales(models.Model):
time_id = models.CharField(max_length=8)
project = models.CharField(max_length=100)
actual_sales = models.DecimalField(max_digits=20, decimal_places=3)
adjustment = models.DecimalField(max_digits=20, decimal_places=3)
def get_budget(self):
bugdesale = BudgetSales.objects.filter(time_id=self.time_id)
if bugdesale.exists():
return bugdesale.first().budget_sales
else:
return None
Serializers.py
class ActualSalesSerializer(serializers.ModelSerializer):
class Meta:
model = ActualSales
fields = ('time_id','project', 'actual_sales', 'adjustment', 'get_budget')