initial

backend/app/models/participant.py

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+from datetime import datetime
+from sqlalchemy import DateTime, ForeignKey, Integer, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+
+class Participant(Base):
+    __tablename__ = "participants"
+    __table_args__ = (
+        UniqueConstraint("user_id", "marathon_id", name="unique_user_marathon"),
+    )
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    user_id: Mapped[int] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    marathon_id: Mapped[int] = mapped_column(ForeignKey("marathons.id", ondelete="CASCADE"), index=True)
+    total_points: Mapped[int] = mapped_column(Integer, default=0)
+    current_streak: Mapped[int] = mapped_column(Integer, default=0)
+    drop_count: Mapped[int] = mapped_column(Integer, default=0)  # For progressive penalty
+    joined_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+
+    # Relationships
+    user: Mapped["User"] = relationship("User", back_populates="participations")
+    marathon: Mapped["Marathon"] = relationship("Marathon", back_populates="participants")
+    assignments: Mapped[list["Assignment"]] = relationship(
+        "Assignment",
+        back_populates="participant",
+        cascade="all, delete-orphan"
+    )