Modular ERP.
Modern stack. Open core.

from fullfinity.engine.base import *

class Invoice(Model):
    _verbose_name = "Invoice"

    customer = ManyToOne("Contact", related_name="invoices", on_delete="RESTRICT")
    date = Date(default=lambda self: date.today())
    state = Selection(
        choices=["Draft", "Posted"],
        default="Draft"
    )

    # Computed field — auto-updates when lines change
    total = Float(calculate="calc_total", store=True)

    @Model.calculate("lines", "lines__amount")
    async def calc_total(self):
        await self.fetch_related("lines")
        self.total = sum(l.amount for l in self.lines)

# Prefetch related records in one query
SaleOrder = get_model("SaleOrder")
orders = await SaleOrder.filter(
    state="Confirmed"
).prefetch_related(
    "customer", "lines", "lines__product"
).all()

# 3 queries total, not 1 + N + N*M
for order in orders:
    print(order.customer.name)
    for line in order.lines:
        print(line.product.name)

# Stored computed field with dependencies
total = Float(calculate="calc_total", store=True)

@Model.calculate("lines", "lines__quantity", "lines__price")
async def calc_total(self):
    await self.fetch_related("lines")
    self.total = sum(
        l.quantity * l.price for l in self.lines
    )
# When any line's quantity or price changes,
# total auto-recomputes and saves to DB