How does Mongodb save data to ensure the integrity of fields?

for example:
my backend model defines an object,

user = {
name: required false,
mobile: required true,
email: required false
}

since my name field and email field are not required, I did not send it at the front end, but passed json:

in the following format
user =  {
mobile: 1118828819
}

the backend receives the json and saves it directly in the MongoDB. When I need to call the user"s information next time, the backend reads the record from the database. However, there is a problem, there are no remaining two fields, which is different from the interface field defined by me and the frontend. How can I solve this problem?

Mar.28,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b30808-2bd03.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b30808-2bd03.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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