how to create user defined id in mongodb rather then _id - node.js

Question

I have a schema to add the book details i wanted to maintain a user defined id called book_id rather than mongodb _id ,
To do that i was making a service call to find the total number documents in the collection and was increment the response by 1 and then assign to book_id
Is there a way to do it only in the server side like we use auto-increment in MySQL

Answer 1

you can define your own _id pattern. also you can add incremental values to _id field of a mongodb collection. but you can't use any field instead of _id. because mongodb cares _id for preventing duplication. mongodb's approach is different any rdbms. but if you want to use book_id, you can use as a field. but a mongodb collection always have _id field.
for your answer, you can read this document.
also in here you can find official mongodb sequence/auto-increment information.
you can apply this code on mongo shell.
db.book_counters.insert(
{
book_id: "bookid",
seq: 0
}
)
function getNextSequence(book) {
var ret = db.book_counters.findAndModify(
{
query: { book_id: book },
update: { $inc: { seq: 1 } },
new: true
}
);
return ret.seq;
}
db.book.insert(
{
book_id: getNextSequence("bookid"),
book: "Harry Potter"
}
)
db.book.insert(
{
book_id: getNextSequence("bookid"),
book: "LOTR"
}
)