Why does dropping the last collection drop the database as well - mongodb

Question

I am trying to delete a collection from database using script file (.js).
My js file is a below
db1 = db.getSiblingDB('Books');
db1.TestBook.drop();
and executing like below
mongo localhost:27017 "d:/test.js"
When my database has multiple collection it is deleting that collection means "TestBook".
But if I try to deleted the last collection it is deleting the database as well.
Can anyone suggest what I am doing wrong.

Answer 1

This appears to be how MongoDB works:
MongoDB Enterprise > db.foo.insert({a:1})
WriteResult({ "nInserted" : 1 })
MongoDB Enterprise > db.getSiblingDB('admin').runCommand({listDatabases:1})
{
"databases" : [
{
"name" : "admin",
"sizeOnDisk" : NumberLong(8192),
"empty" : false
},
{
"name" : "config",
"sizeOnDisk" : NumberLong(12288),
"empty" : false
},
{
"name" : "local",
"sizeOnDisk" : NumberLong(8192),
"empty" : false
},
{
"name" : "test",
"sizeOnDisk" : NumberLong(8192),
"empty" : false
}
],
"totalSize" : NumberLong(36864),
"totalSizeMb" : NumberLong(0),
"ok" : 1
}
MongoDB Enterprise > db.foo.drop()
true
MongoDB Enterprise > db.getSiblingDB('admin').runCommand({listDatabases:1})
{
"databases" : [
{
"name" : "admin",
"sizeOnDisk" : NumberLong(8192),
"empty" : false
},
{
"name" : "config",
"sizeOnDisk" : NumberLong(12288),
"empty" : false
},
{
"name" : "local",
"sizeOnDisk" : NumberLong(8192),
"empty" : false
}
],
"totalSize" : NumberLong(28672),
"totalSizeMb" : NumberLong(0),
"ok" : 1
}
However, it appears that the database retains at least some of the configured state for the dropped database. For example, if you enable sharding on a database, then drop the last collection, then try to enable sharding on a new collection in that database, sharding on the collection will be enabled which requires the sharding to have already been enabled on the database.
Dropping collections does change the list of returned databases, which could be problematic for applications. You can report this as an issue via https://jira.mongodb.org/browse/server if you like.