MongoDB: Custom command defined in .mongorc.js

Question

I'd like to define a custom Mongo shell command. Given .mongorc.js is like below:

var dbuc;

(function () {
    dbuc = (function () {
        return db.getName().toUpperCase();
    })();
})();

I'm getting proper upper-cased name for initial database, yet when I switch to other database I'm still getting name of the initial database instead of current one.

> db
test
> dbuc
TEST

> use otherbase

> db
otherbase
> dbuc
TEST

I see .mongorc.js is run before mongo runs and that's why dbuc variable has assigned value of initial database - test. But I rather wonder how to get a name of current database whatever base I turned on.

Abhijit · Accepted Answer · 2020-11-21 16:59:33Z

2

There are a few things to note:

In mongo shell, typeof db is a javascript object and typeof dbuc is string.
I believe, in your code, dbuc value is assigned once and does not change when use is called.
use is a shellHelper function(type shellHelper.use in mongo shell). It reassigns variable db with newly returned database object.

One of the solutions, for dbuc to work, is to add following code to .mongorc.js

// The first time mongo shell loads, assign the value of dbuc. 
dbuc = db.getName().toUpperCase();

shellHelper.use = function (dbname) {
    var s = "" + dbname;
    if (s == "") {
        print("bad use parameter");
        return;
    }
    db = db.getMongo().getDB(dbname);

    // After new assignment, extract and assign upper case 
    // of newly assgined db name to dbuc.
    dbuc = db.getName().toUpperCase();

    print("switched to db " + db.getName());
};

edited Nov 21, 2020 at 16:59

Abhijit

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answered Sep 13, 2016 at 3:54

Nishant Bhardwaj

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