第二步

backend/app/models/document_category.py

@@ -0,0 +1,41 @@
+"""DocumentCategory 文档分类模型。"""
+
+from sqlalchemy import ForeignKey, Integer, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base, TimestampMixin, UUIDPrimaryKeyMixin
+
+
+class DocumentCategory(UUIDPrimaryKeyMixin, TimestampMixin, Base):
+    """文档分类模型。
+
+    技术审查 §2.2：document_categories 表。
+    """
+
+    __tablename__ = "document_categories"
+
+    knowledge_base_id: Mapped[str] = mapped_column(
+        String(32),
+        ForeignKey("knowledge_bases.id"),
+        nullable=False,
+        index=True,
+        comment="所属知识库 ID",
+    )
+    name: Mapped[str] = mapped_column(
+        String(255),
+        nullable=False,
+        comment="分类名称",
+    )
+    sort_order: Mapped[int] = mapped_column(
+        Integer,
+        default=0,
+        nullable=False,
+        comment="排序序号",
+    )
+
+    # 关系
+    knowledge_base = relationship("KnowledgeBase", back_populates="categories", lazy="selectin")
+    documents = relationship("Document", back_populates="category", lazy="selectin")
+
+    def __repr__(self) -> str:
+        return f"<DocumentCategory {self.name!r} (kb={self.knowledge_base_id!r})>"