How does the node operation mongodb get a specified amount of data in an embedded object? Ask for guidance!

Database table information:

var registerSchema = new mongoose.Schema({
    email: String,
    name: String,
    password: String,
    img: String,
    hero: [],
    sex: String,
    hobby: String,
    signature: String
});

data visualization:

hero:

hero
.limit()hero


:


user.find (). Limit (). Then ()

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-64f5-1b33074-2be64.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b33074-2be64.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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