Create root user on MongoDB

gistfile1.txt

// to drop all databases
mongo --quiet --eval 'db.getMongo().getDBNames().forEach(function(i){db.getSiblingDB(i).dropDatabase()})'


use admin;
db.createUser(
  {
    user: "user",
    pwd: "pass",
    roles: [ "root" ]
  }
);

use database;
db.createUser(
  {
    user: "user",
    pwd: "pass",
    roles: [ { role: "readWrite", db: "database" } ]
  }
);


//--------------------------------------------------


db
  .getMongo()
  .getDBNames()
  .filter(n => !['admin','local','config'].includes(n))
  .forEach(dname =>
    db
      .getMongo()
      .getDB(dname)
      .dropDatabase()
  )
;

One-liner:

db.getMongo().getDBNames().filter(n => !['admin','local','config'].includes(n)).forEach(dname =>    db.getMongo().getDB(dname).dropDatabase());

This drops all DBs but preserves MongoDB's internal collections.
//------

Save this to drop_all_dbs.js:

var databases = db.getMongo().getDBNames()
for(var i in databases){
    db = db.getMongo().getDB( databases[i] );
    if(db.getName() == "admin" || db.getName() == "local"){
        print("skipping db " + db.getName())
        continue
    }
    print( "dropping db " + db.getName() );
    db.dropDatabase();
}
Now you can execute:

mongo drop_all_dbs.js
//---------------------------------------------------------------

docker exec mongodb sh -c "mongo --quiet --eval 'db.getMongo().getDBNames().forEach(function(i){db.getSiblingDB(i).dropDatabase()})'"