rails console返回零

Question

我正在尝试从rails控制台中提取日期，但是当操作最后一次发生时仍会返回nil

检查特定值（expire_at）时

[12] pry(main)> User.last.store_credit
  User Load (3.2ms)  SELECT  "users".* FROM "users"  ORDER BY "users"."id" DESC LIMIT 1
  StoreCredit Load (2.0ms)  SELECT  "store_credits".* FROM "store_credits" WHERE "store_credits"."user_id" = $1 LIMIT 1  [["user_id", 2]]
=> #<StoreCredit:0x007fab4b5ba6a0 id: 2, amount: #<BigDecimal:7fab4b5b9930,'0.2E2',9(18)>, user_id: 2, expire_at: nil, last_expired_at: nil, created_at: nil, updated_at: nil>

显示所有字段时

SELECT t.* FROM public.store_credits t

但是当我运行此查询时，我会看到出现的值

In [271]: df
Out[271]: 
   col1  col2
0    23    33
1    42    11

In [272]: df['col3'] = (df['col1'].map(str) + ',' + df['col2'].map(str))

In [273]: df
Out[273]: 
   col1  col2   col3
0    23    33  23,33
1    42    11  42,11