Step 1: Add PricingConfig model and PricingRepository

- Create PricingConfig model with all required fields (premium settings, trade limits)
- Implement PricingRepository with singleton pattern (get_current, create_or_update)
- Add comprehensive tests for repository functionality
- Export model and repository in __init__.py files

backend/models/__init__.py

@@ -14,6 +14,7 @@ from .enums import (
 from .exchange import Exchange
 from .invite import Invite
 from .price_history import PriceHistory
+from .pricing_config import PricingConfig
 
 # Export role configuration
 from .role_config import ROLE_ADMIN, ROLE_DEFINITIONS, ROLE_REGULAR
@@ -34,6 +35,7 @@ __all__ = [
     "InviteStatus",
     "Permission",
     "PriceHistory",
+    "PricingConfig",
     "Role",
     "RoleConfig",
     "TradeDirection",

backend/models/pricing_config.py

@@ -0,0 +1,44 @@
+from datetime import UTC, datetime
+
+from sqlalchemy import DateTime, Integer
+from sqlalchemy.orm import Mapped, mapped_column
+
+from database import Base
+
+
+class PricingConfig(Base):
+    """Pricing configuration for exchange trades.
+
+    Singleton pattern: Only one record should exist in the database.
+    Updates modify the existing record rather than creating new ones.
+    """
+
+    __tablename__ = "pricing_config"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+
+    # Premium settings
+    premium_buy: Mapped[int] = mapped_column(Integer, nullable=False)  # -100 to 100
+    premium_sell: Mapped[int] = mapped_column(Integer, nullable=False)  # -100 to 100
+    small_trade_threshold_eur: Mapped[int] = mapped_column(
+        Integer, nullable=False
+    )  # EUR cents, e.g., 20000 = €200
+    small_trade_extra_premium: Mapped[int] = mapped_column(
+        Integer, nullable=False
+    )  # -100 to 100
+
+    # Trade amount limits (EUR cents)
+    eur_min_buy: Mapped[int] = mapped_column(Integer, nullable=False)
+    eur_max_buy: Mapped[int] = mapped_column(Integer, nullable=False)
+    eur_min_sell: Mapped[int] = mapped_column(Integer, nullable=False)
+    eur_max_sell: Mapped[int] = mapped_column(Integer, nullable=False)
+
+    # Timestamps
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(UTC),
+        onupdate=lambda: datetime.now(UTC),
+    )