Databases & Collections

A MongoDB server can hold many databases, each made of collections — the rough equivalent of tables, except a collection doesn't require every document to share the same shape.

Switching to a database

use switches your session to a database, creating it implicitly the first time you insert something into it:

JS mongosh

use blogdb

Output

switched to db blogdb

Note: use blogdb alone doesn't actually create the database yet — MongoDB only creates it, for real, once you insert at least one document. Run show dbs right after a plain use and you likely won't see it listed until you've written something.

Creating a collection

Collections are usually created implicitly on first insert, but you can also create one explicitly, which is useful when you want to set options up front (like a validation schema):

JS mongosh

db.createCollection("posts")

Output

{ ok: 1 }

Listing what exists

JS mongosh

show dbs

Output

admin     40.00 KiB
blogdb   8.00 KiB
config    12.00 KiB
local     72.00 KiB

JS mongosh

show collections

Output

posts

Unlike a SQL table, posts here has no defined columns — every document you insert into it can carry a different set of fields, though in practice most real applications keep documents in one collection reasonably consistent on purpose.

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