刪除/收回数据需要特別指定 action 為 delete，所有有 ref 的其他地方也會一併被移除。

因为在区块链 DB 上，所以往回找数据都还是会找到，只是对于当前最新数据状态已经移除。

1. 删除数据

删除一样是在 id 处用两个来指定：[ <predicate>, <object> ]

[
   {
      "_id":[
         "user/wallet",  // predicate
         "0x7EA1EaA27b313D04D359bF3e654FE927376e31Bc" // object
      ],
      "_action": "delete"
   }
]

cURL 指令：

# linux
curl -H "Accept: application/json" -X POST -d '[{"_id":["user\\/wallet","0x7EA1EaA27b313D04D359bF3e654FE927376e31Bc"],"_action":"delete"}]' <http://13.114.145.25/fdb/seedao/testing/transact>

# windows
curl -H "Accept: application/json" -X POST -d "[{\\"_id\\":[\\"user\\/wallet\\",\\"0x7EA1EaA27b313D04D359bF3e654FE927376e31Bc\\"],\\"_action\\":\\"delete\\"}]" <http://13.114.145.25/fdb/seedao/testing/transact>

这时候查询就找不到了：

[
   {
      "_id":351843720888323,
      "user/wallet":"0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd3",
      "user/email":"[email protected]"
   },
   {
      "_id":351843720888321,
      "user/wallet":"0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd2",
      "user/email":"[email protected]"
   },
   {
      "_id":351843720888320,
      "user/wallet":"0x7EA1EaA27b313D04D359bF3e654FE927376e31Bb",
      "user/email":"[email protected]"
   }
]

2. 删除谓词 (Predicate) 数据

如果是要删除某一个 data 的某个 predicate 的值，可以使用 null

[
   {
      "_id":[
         "user/wallet",
         "0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd3"
      ],
      "email": null
   }
]

cURL 指令：

# linux
curl -H "Accept: application/json" -X POST -d '[{"_id":["user/wallet","0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd3"],"email":null}]' <http://13.114.145.25/fdb/seedao/testing/transact>

# windows
curl -H "Accept: application/json" -X POST -d "[{\\"_id\\":[\\"user/wallet\\",\\"0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd3\\"],\\"email\\":null}]" <http://13.114.145.25/fdb/seedao/testing/transact>

我们再看数据就会发现指定 wallet 的 email 为空：

[
   {
      "_id":351843720888323,
      "user/wallet":"0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd3"
　　　 // email 不见了
   },
   {
      "_id":351843720888321,
      "user/wallet":"0x5e6CcE07A609D7550Ffd39beEa0d8B2eeF28FCd2",
      "user/email":"[email protected]"
   },
   {
      "_id":351843720888320,
      "user/wallet":"0x7EA1EaA27b313D04D359bF3e654FE927376e31Bb",
      "user/email":"[email protected]"
   }
]