MongoDB Collections

Show Collections

show collections (or show tables) lists every collection in the currently selected database.

use rahultechnology
show collections
// emp
show tables
// emp

Create a Collection

MongoDB stores documents in collections — the equivalent of tables in a relational database. There are two ways to create one:

1. Explicitly, with createCollection():

db.createCollection("emp1")
// { ok: 1 }

2. Implicitly, by inserting into it:

db.emp2.insertOne({ name: "rahul" })
// A collection named "emp2" is created automatically if it doesn't exist.

show collections
// emp
// emp1
// emp2

Rename a Collection

Use db.collection.renameCollection() to fix a typo'd or outdated collection name without losing its data.

db.emp1.renameCollection("emp11")
// { ok: 1 }

show collections
// emp
// emp11
// emp2

Delete / Drop a Collection

db.collection.drop() permanently deletes a collection. It returns true on success — once dropped, the data cannot be recovered.

db.emp.drop()
// true

db.emp1.drop()
// false  (already renamed, so it no longer exists)

show collections

Common Errors & Troubleshooting

• MongoServerError: Collection already exists — thrown by createCollection() if you try to explicitly create a collection that already exists. Check show collections first, or just skip createCollection() and let an insert create it implicitly.
• A dropped collection's data is unrecoverable — drop() has no undo. If you're not certain, rename it first with renameCollection() (or take a backup with mongodump) instead of dropping outright.
• Renaming to a name that already exists — renameCollection() fails by default if the target name is taken; pass renameCollection("newName", true) to explicitly allow overwriting it (drops the old target collection first).

Key Takeaways

• A collection can be created explicitly (createCollection()) or automatically on first insert.
• renameCollection() renames in place — no data is lost.
• drop() is permanent — there is no "undo" or recycle bin.