feat(purchase): 新增采购申请模块后端（模型+Service+API路由）

inventory-backend/app/models/purchase.py

@@ -0,0 +1,86 @@
+import json
+from app.extensions import db, beijing_time
+from datetime import datetime
+
+
+class PurchaseRequest(db.Model):
+    """
+    采购申请表
+    """
+    __tablename__ = 'purchase_request'
+
+    id = db.Column(db.Integer, primary_key=True)
+    request_no = db.Column(db.String(100), unique=True, nullable=False, index=True)
+    name = db.Column(db.String(255), nullable=False, comment='采购名称')
+    spec_model = db.Column(db.String(255), comment='规格型号')
+    quantity = db.Column(db.Numeric(19, 4), nullable=False, comment='采购数量')
+    purchase_date = db.Column(db.Date, nullable=False, comment='采购时间')
+    supplier_link = db.Column(db.String(500), comment='商家地址链接')
+    remark = db.Column(db.Text, comment='备注信息')
+    images = db.Column(db.Text, comment='图片列表JSON')
+    unit_price = db.Column(db.Numeric(19, 4), default=0, comment='单价')
+    total_price = db.Column(db.Numeric(19, 4), default=0, comment='总价')
+    status = db.Column(db.Integer, default=0, nullable=False)
+    requester_id = db.Column(db.Integer, nullable=False, index=True)
+    approver_id = db.Column(db.Integer, index=True)
+    approved_at = db.Column(db.DateTime)
+    reject_reason = db.Column(db.Text)
+    created_at = db.Column(db.DateTime, default=beijing_time, nullable=False)
+    updated_at = db.Column(db.DateTime, default=beijing_time, onupdate=beijing_time, nullable=False)
+
+    def _safe_parse_json(self, value):
+        if value is None:
+            return []
+        if isinstance(value, (list, dict)):
+            return value
+        if isinstance(value, str):
+            val = value.strip()
+            if not val:
+                return []
+            try:
+                parsed = json.loads(val)
+                return parsed if isinstance(parsed, list) else []
+            except Exception:
+                return []
+        return []
+
+    def get_images(self):
+        return self._safe_parse_json(self.images)
+
+    def set_images(self, image_list):
+        self.images = json.dumps(image_list, ensure_ascii=False) if image_list else '[]'
+
+    def _get_user_name(self, user_id):
+        if not user_id:
+            return ""
+        from app.models.system import SysUser
+        try:
+            user = db.session.get(SysUser, user_id)
+            return user.username if user else f"未知用户({user_id})"
+        except Exception:
+            return f"用户({user_id})"
+
+    def to_dict(self):
+        return {
+            'id': self.id,
+            'request_no': self.request_no,
+            'name': self.name,
+            'spec_model': self.spec_model or '',
+            'quantity': float(self.quantity) if self.quantity else 0,
+            'purchase_date': self.purchase_date.strftime('%Y-%m-%d') if self.purchase_date else None,
+            'supplier_link': self.supplier_link or '',
+            'remark': self.remark or '',
+            'images': self.get_images(),
+            'unit_price': float(self.unit_price) if self.unit_price else 0,
+            'total_price': float(self.total_price) if self.total_price else 0,
+            'status': self.status,
+            'status_text': ['待审批', '已通过', '已驳回', '已完成'][self.status] if self.status in [0, 1, 2, 3] else '未知',
+            'requester_id': self.requester_id,
+            'requester_name': self._get_user_name(self.requester_id),
+            'approver_id': self.approver_id,
+            'approver_name': self._get_user_name(self.approver_id) if self.approver_id else None,
+            'approved_at': self.approved_at.strftime('%Y-%m-%d %H:%M:%S') if self.approved_at else None,
+            'reject_reason': self.reject_reason or '',
+            'created_at': self.created_at.strftime('%Y-%m-%d %H:%M:%S') if self.created_at else None,
+            'updated_at': self.updated_at.strftime('%Y-%m-%d %H:%M:%S') if self.updated_at else None,
+        }