修改delete相关代码逻辑，新增README_students.md用来做模块解释。

students/dao/students_dao.py

@@ -112,33 +112,45 @@ def update_student_dao( s , db):
 # 逻辑删除/软删除
 def delete_student_dao( s , db):
     try:
+        if not any([s.get('sid')
+                       ,s.get("student_name")
+                       ,s.get("student_phone")
+                       ,s.get("class_name")
+                       ,s.get("job_open_time")
+                       ,s.get("offer_issue_time")
+                       ,s.get("company_name")
+                       ,s.get("salary")
+                    ]):
+            raise HTTPException(status_code=400, detail="输入需要删除的学生信息，删除条件任选，但不可全为空。")
         q = db.query(Students).filter(Students.is_deleted == False)
         if s.get('sid'):
-            q = q.filter(Students.sid == s.sid)
+            q = q.filter(Students.sid == s.get("sid") )
         if s.get('student_name'):
-            q = q.filter(Students.student_name == s.student_name)
+            q = q.filter(Students.student_name == s.get("student_name") )
         if s.get("student_phone"):
-            q = q.filter(Students.student_phone == s.student_phone)
+            q = q.filter(Students.student_phone == s.get("student_phone") )
         if s.get('class_name'):
-            q = q.filter(Students.class_name == s.class_name)
+            q = q.filter(Students.class_name == s.get("class_name") )
         if s.get('job_open_time'):
-            q = q.filter(Students.job_open_time == s.job_open_time)
+            q = q.filter(Students.job_open_time == s.get("job_open_time") )
         if s.get('offer_issue_time'):
-            q = q.filter(Students.offer_issue_time == s.offer_issue_time)
+            q = q.filter(Students.offer_issue_time == s.get("offer_issue_time") )
         if s.get('company_name'):
-            q = q.filter(Students.company_name == s.company_name)
+            q = q.filter(Students.company_name == s.get("company_name") )
         if s.get('salary'):
-            q = q.filter(Students.salary >= s.salary)
+            q = q.filter(Students.salary >= s.get("salary") )
         s1_delete = q.all()
         if not s1_delete:
-            raise HTTPException(status_code=404, detail="Student not found")
+            raise HTTPException(status_code=404, detail="没有找到该学生。")
         for i in s1_delete:
             i.is_deleted = True
             i.deleted_date = datetime.now()
-        s2_deleted =[{"删除的学生ID":i.sid,"删除的学生姓名":i.student_name,"删除的学生电话":i.student_phone}for i in s1_delete]
+        s2_deleted =[{"sid":i.sid,"student_name":i.student_name,"student_phone":i.student_phone}for i in s1_delete]
+    except HTTPException:
+        raise
     except Exception:
         db.rollback()
-        return False
+        raise HTTPException(status_code=500, detail="Internal server error")
     else:
         db.commit()
         return s2_deleted