Soft delete pattern in MongoDB - Step-by-Step Execution

Concept Flow - Soft delete pattern in MongoDB

Start: Document exists

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Update document: set deleted flag

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Document marked as deleted

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Queries exclude deleted documents

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Document hidden but still in DB

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Optional: Restore by unsetting deleted flag

The soft delete pattern updates a document to mark it as deleted instead of removing it, so queries exclude it but data remains.

Execution Sample

MongoDB

db.users.updateOne({_id: 1}, {$set: {deleted: true}})
db.users.find({deleted: {$ne: true}})

Marks a user as deleted and then queries only users not marked deleted.

Execution Table

Step	Action	Query/Update	Result/Effect
1	Initial state	db.users.find({})	[{_id:1, name:'Alice'}, {_id:2, name:'Bob'}]
2	Soft delete user 1	db.users.updateOne({_id:1}, {$set: {deleted:true}})	User 1 document updated with deleted:true
3	Query excluding deleted	db.users.find({deleted: {$ne:true}})	[{_id:2, name:'Bob'}]
4	Restore user 1	db.users.updateOne({_id:1}, {$unset: {deleted: 1}})	User 1 document deleted flag removed
5	Query excluding deleted	db.users.find({deleted: {$ne:true}})	[{_id:1, name:'Alice'}, {_id:2, name:'Bob'}]
6	Hard delete user 2	db.users.deleteOne({_id:2})	User 2 document removed from collection
7	Final query	db.users.find({deleted: {$ne:true}})	[{_id:1, name:'Alice'}]

💡 Execution ends after final query showing only non-deleted documents.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	Final
users collection	[{_id:1, name:'Alice'}, {_id:2, name:'Bob'}]	[{_id:1, name:'Alice', deleted:true}, {_id:2, name:'Bob'}]	[{_id:1, name:'Alice'}, {_id:2, name:'Bob'}]	[{_id:1, name:'Alice'}]	[{_id:1, name:'Alice'}]

Key Moments - 3 Insights

Why does the soft deleted document still exist in the database?

Because the update sets a 'deleted' flag instead of removing the document, so it stays but is marked as deleted (see Step 2 in execution_table).

How do queries exclude soft deleted documents?

Queries add a condition to exclude documents where 'deleted' is true, like {deleted: {$ne:true}}, shown in Steps 3 and 5.

What is the difference between soft delete and hard delete here?

Soft delete marks the document with a flag (Step 2), hard delete removes it completely (Step 6).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of the query at Step 3?

A [{_id:2, name:'Bob'}]

B [{_id:1, name:'Alice'}]

C [{_id:1, name:'Alice'}, {_id:2, name:'Bob'}]

D []

💡 Hint

Check the 'Result/Effect' column for Step 3 in execution_table.

At which step is the 'deleted' flag removed from user 1?

A Step 2

B Step 6

C Step 4

D Step 7

💡 Hint

Look at the 'Action' and 'Query/Update' columns in execution_table for when $unset is used.

If we never ran Step 6, what would the final query at Step 7 return?

A [{_id:1, name:'Alice'}]

B [{_id:1, name:'Alice'}, {_id:2, name:'Bob'}]

C []

D [{_id:2, name:'Bob'}]

💡 Hint

Check variable_tracker to see if user 2 is removed or not after Step 6.

Concept Snapshot

Soft delete in MongoDB:
- Update document with a 'deleted' flag instead of removing.
- Queries exclude documents where deleted:true.
- Allows restoring by unsetting the flag.
- Hard delete removes document permanently.
- Keeps data for audit or recovery.

Full Transcript

The soft delete pattern in MongoDB means marking a document as deleted by adding a flag instead of deleting it. This keeps the data but hides it from normal queries by filtering out documents with the deleted flag. You update the document with {$set: {deleted: true}} to soft delete it. Queries then use {deleted: {$ne: true}} to exclude these. You can restore by removing the flag with {$unset: {deleted: ''}}. Hard delete removes the document completely. This pattern helps keep data safe and recoverable while hiding it from users.