How to save array object data to mongodb using mongoose and node.js

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MongoDB

Node.js

mongoose

Please help.

I am using mongoose, mongodb and node.js

I am trying to save data array object. But, in mongodb the field always empty.
My field in mongodb is "tag"

It should be contain data like :

[
{tag_title: "Art", _tagId: "5f8d0b32f7074616e46cf923"}, 
{tag_title: "Artistic", _tagId: "5f8d0b32f7074616e46cf875"}
]

My codes : cl - Pastebin.com[^]

I have tried this solution: Mongoose ODM[^] but not work.

What I have tried:

Set mongoose schema to:

tag: [{
    tag_title: {
        type: String,
    },
    _tagId: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Tag'
    }
}],