Python SQLAlchemy Pydantic في الممارسة: الكود والأوامر التي تهم حقاً

erp/
├── alembic.ini
├── migrations/
├── app/
│   ├── core/
│   │   ├── config.py            # الإعدادات
│   │   └── database.py
│   ├── models/
│   │   ├── customer.py
│   │   ├── product.py
│   │   ├── order.py
│   │   └── invoice.py
│   ├── schemas/                 # مخططات Pydantic للإدخال/الإخراج
│   ├── services/                # منطق الأعمال
│   ├── api/                     # مسارات FastAPI
│   └── main.py
└── tests/

import enum
from sqlalchemy.orm import Mapped, mapped_column, relationship
from sqlalchemy import ForeignKey
from datetime import datetime

class CustomerType(str, enum.Enum):
    B2B = "b2b"
    B2C = "b2c"

class Customer(Base):
    __tablename__ = "customers"
    id: Mapped[int] = mapped_column(primary_key=True)
    type: Mapped[CustomerType]
    name: Mapped[str]
    email: Mapped[str] = mapped_column(unique=True)
    tax_id: Mapped[str | None]              # لـ B2B
    created_at: Mapped[datetime] = mapped_column(default=datetime.utcnow)
    
    addresses: Mapped[list["Address"]] = relationship(back_populates="customer", cascade="all")
    orders: Mapped[list["Order"]] = relationship(back_populates="customer")

class Address(Base):
    __tablename__ = "addresses"
    id: Mapped[int] = mapped_column(primary_key=True)
    customer_id: Mapped[int] = mapped_column(ForeignKey("customers.id"))
    street: Mapped[str]
    city: Mapped[str]
    zip_code: Mapped[str]
    country: Mapped[str]
    is_billing: Mapped[bool] = mapped_column(default=False)
    is_shipping: Mapped[bool] = mapped_column(default=True)
    
    customer: Mapped["Customer"] = relationship(back_populates="addresses")

from decimal import Decimal

class Product(Base):
    __tablename__ = "products"
    id: Mapped[int] = mapped_column(primary_key=True)
    sku: Mapped[str] = mapped_column(unique=True)
    name: Mapped[str]
    price: Mapped[Decimal] = mapped_column(Numeric(10, 2))
    vat_rate: Mapped[Decimal] = mapped_column(Numeric(4, 2), default=Decimal("20.00"))
    active: Mapped[bool] = mapped_column(default=True)
    
    stocks: Mapped[list["Stock"]] = relationship(back_populates="product")

class Warehouse(Base):
    __tablename__ = "warehouses"
    id: Mapped[int] = mapped_column(primary_key=True)
    code: Mapped[str] = mapped_column(unique=True)
    name: Mapped[str]

class Stock(Base):
    __tablename__ = "stocks"
    id: Mapped[int] = mapped_column(primary_key=True)
    product_id: Mapped[int] = mapped_column(ForeignKey("products.id"))
    warehouse_id: Mapped[int] = mapped_column(ForeignKey("warehouses.id"))
    quantity: Mapped[int] = mapped_column(default=0)
    
    __table_args__ = (
        UniqueConstraint("product_id", "warehouse_id"),
        CheckConstraint("quantity >= 0"),
    )
    
    product: Mapped["Product"] = relationship(back_populates="stocks")

class OrderStatus(str, enum.Enum):
    DRAFT = "draft"
    CONFIRMED = "confirmed"
    SHIPPED = "shipped"
    DELIVERED = "delivered"
    CANCELLED = "cancelled"

class Order(Base):
    __tablename__ = "orders"
    id: Mapped[int] = mapped_column(primary_key=True)
    customer_id: Mapped[int] = mapped_column(ForeignKey("customers.id"))
    reference: Mapped[str] = mapped_column(unique=True)
    status: Mapped[OrderStatus] = mapped_column(default=OrderStatus.DRAFT)
    created_at: Mapped[datetime] = mapped_column(default=datetime.utcnow)
    
    customer: Mapped["Customer"] = relationship(back_populates="orders")
    lines: Mapped[list["OrderLine"]] = relationship(back_populates="order", cascade="all, delete-orphan")
    invoice: Mapped["Invoice"] = relationship(back_populates="order", uselist=False)

class OrderLine(Base):
    __tablename__ = "order_lines"
    id: Mapped[int] = mapped_column(primary_key=True)
    order_id: Mapped[int] = mapped_column(ForeignKey("orders.id"))
    product_id: Mapped[int] = mapped_column(ForeignKey("products.id"))
    quantity: Mapped[int] = mapped_column()
    unit_price: Mapped[Decimal] = mapped_column(Numeric(10, 2))
    
    order: Mapped["Order"] = relationship(back_populates="lines")
    product: Mapped["Product"] = relationship()

class Invoice(Base):
    __tablename__ = "invoices"
    id: Mapped[int] = mapped_column(primary_key=True)
    order_id: Mapped[int] = mapped_column(ForeignKey("orders.id"), unique=True)
    number: Mapped[str] = mapped_column(unique=True)
    issued_at: Mapped[datetime] = mapped_column(default=datetime.utcnow)
    subtotal: Mapped[Decimal] = mapped_column(Numeric(10, 2))
    vat: Mapped[Decimal] = mapped_column(Numeric(10, 2))
    total: Mapped[Decimal] = mapped_column(Numeric(10, 2))
    paid: Mapped[bool] = mapped_column(default=False)
    
    order: Mapped["Order"] = relationship(back_populates="invoice")

class StockMovement(Base):
    __tablename__ = "stock_movements"
    id: Mapped[int] = mapped_column(primary_key=True)
    product_id: Mapped[int] = mapped_column(ForeignKey("products.id"))
    warehouse_id: Mapped[int] = mapped_column(ForeignKey("warehouses.id"))
    quantity: Mapped[int]                            # سالب = خروج
    reason: Mapped[str]                              # "order_123", "restock"
    created_at: Mapped[datetime] = mapped_column(default=datetime.utcnow)