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Implementing Soft Deletes: Full Detailed Guide

1. Introduction

In database systems, soft deletes refer to marking records as deleted without actually removing them from the database. Instead of executing a DELETE SQL command that physically removes a row, we use an update operation to set a flag (commonly a boolean like is_deleted) or a timestamp (like deleted_at) indicating the record has been logically deleted.

This method helps maintain historical data, audit trails, restore mistakenly deleted records, and ensure compliance with data retention policies.

2. Why Use Soft Deletes?

Before implementation, it’s important to understand why soft deletes are important:

Data Recovery: Restore accidentally deleted records.
Audit Compliance: Proof of actions for audits (legal or regulatory).
Referential Integrity: Avoid orphaning records in related tables.
Business Intelligence: Analyze deleted vs. active records.
Undo/Redo Mechanisms: Support features like “Trash” or “Recycle Bin.”

3. Challenges Without Soft Deletes

If soft deletes are not used:

Permanent deletion could result in loss of critical data.
Cascading deletes could unintentionally destroy dependent data.
Auditing actions become harder.
Recovery from deletion mistakes is impossible unless backups are used.

4. Core Concepts in Soft Deletes

Soft delete strategies revolve around a few key concepts:

Concept	Description
Deleted Flag	Boolean field like `is_deleted` to mark deletion.
Deletion Timestamp	Field like `deleted_at` capturing when the deletion happened.
Filtering Queries	Adjusting SELECT queries to exclude soft-deleted rows unless specifically requested.
Partial Restoration	Un-deleting a record by clearing the delete marker.

5. Key Design Decisions

When designing for soft deletes, consider:

Approach: Boolean flag vs. timestamp.
Default Queries: Always exclude deleted rows.
Security: Prevent unauthorized restoration.
Cascading Soft Deletes: Related records should also be marked as deleted.
Permanent Deletion (Hard Delete): For final removal if needed.
UI Considerations: Show deleted items in admin panels (Trash/Archive views).

6. Step-by-Step Implementation

Step 1: Define the Schema

You need to add soft delete fields to your tables.

Option A: Boolean Flag Approach

ALTER TABLE employees
ADD COLUMN is_deleted BOOLEAN DEFAULT FALSE;

Pros: Easy to query.
Cons: No information about when it was deleted.

Option B: Timestamp Approach

ALTER TABLE employees
ADD COLUMN deleted_at TIMESTAMP NULL;

Pros: Know exactly when it was deleted.
Cons: Slightly more complex queries.

Step 2: Update Application Logic

Instead of running a DELETE operation, modify your app to update the record.

UPDATE employees
SET is_deleted = TRUE
WHERE id = 123;

UPDATE employees
SET deleted_at = NOW()
WHERE id = 123;

Step 3: Modify SELECT Queries

To hide deleted records from normal user views:

SELECT * FROM employees WHERE is_deleted = FALSE;

SELECT * FROM employees WHERE deleted_at IS NULL;

Important: Update every retrieval endpoint or function to respect the soft delete condition.

Step 4: Create Scopes or Views

You can abstract the logic by creating:

Database Views
ORM Scopes

SQL View Example

CREATE VIEW active_employees AS
SELECT * FROM employees WHERE is_deleted = FALSE;

ORM Scope Example (e.g., Laravel)

public function scopeActive($query)
{
    return $query->whereNull('deleted_at');
}

Step 5: Handling Restore

To undelete a record:

UPDATE employees
SET is_deleted = FALSE
WHERE id = 123;

UPDATE employees
SET deleted_at = NULL
WHERE id = 123;

In the app, you could create a “Restore” button.

Step 6: Permanent Deletion Option (Hard Delete)

For records that must be fully removed after time:

DELETE FROM employees
WHERE is_deleted = TRUE
AND deleted_at < NOW() - INTERVAL '30 days';

Schedule this through background jobs or cron tasks.

7. Advanced Topics

7.1 Cascading Soft Deletes

When a parent record is soft-deleted, child records may also need soft-deletion.

Example: Deleting a User and their Posts

User Table: users
Posts Table: posts

When a user is soft-deleted, all their posts must be soft-deleted too.

Solutions:

Trigger-based cascading soft deletes.
Application-level cascading (handle it in service layer).

Example Trigger

CREATE OR REPLACE FUNCTION soft_delete_user_posts()
RETURNS TRIGGER AS $$
BEGIN
    UPDATE posts SET is_deleted = TRUE WHERE user_id = OLD.id;
    RETURN OLD;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER user_soft_delete
AFTER UPDATE OF is_deleted ON users
FOR EACH ROW
WHEN (OLD.is_deleted IS DISTINCT FROM TRUE AND NEW.is_deleted = TRUE)
EXECUTE FUNCTION soft_delete_user_posts();

7.2 Multi-Tenant Soft Deletes

In SaaS apps, ensure soft deletes are tenant-aware:

SELECT * FROM employees
WHERE tenant_id = 456 AND is_deleted = FALSE;

7.3 Soft Delete with Versioning

Maintain multiple versions of a record (useful in auditing systems).

Instead of updating the same row, you insert a new row with version_number.
Deleting means creating a new version with deleted status.

7.4 Soft Delete and Indexing

Ensure indexes include soft delete flags for query optimization:

CREATE INDEX idx_employees_active
ON employees (is_deleted)
WHERE is_deleted = FALSE;

7.5 Soft Deletes in Different Databases

MySQL/PostgreSQL: Very common with views or scopes.
MongoDB: Update documents with a deletedAt field.
Cassandra: Usually use TTLs, but can simulate soft deletes.

8. Common Mistakes to Avoid

Forgetting to filter deleted records: causes “ghost records” to appear.
Soft deleting without cascading: leads to “zombie” child records.
Using only a flag without timestamps: makes tracking harder.
Allowing deletes from non-admins: opens up abuse.
Never purging soft-deleted data: bloats the database.
Not creating proper indexes: slows down queries.

9. Real-World Examples

9.1 Gmail “Trash”

Emails are moved to “Trash” (soft delete).
After 30 days, they are permanently deleted.

9.2 E-commerce “Archived Orders”

Orders soft-deleted to prevent accidental data loss.
Admins can view or restore orders.

Soft deletes offer a powerful and flexible way to handle data deletion safely. By designing a thoughtful soft delete mechanism, businesses can ensure data recoverability, audit readiness, and stronger integrity while maintaining optimal database performance.

If properly managed, a soft delete strategy becomes an essential part of robust enterprise application design.

🚀 Summary Table

Aspect	Description
What	Marking records as deleted without removing
Fields	`is_deleted` boolean, `deleted_at` timestamp
Queries	Always filter active records
Restore	Clear deletion marker
Permanent Delete	Scheduled removal process
Advanced	Cascading deletes, tenant-aware, indexing
Caution	Ensure all queries, triggers, and indexes are correct

Would you also like me to provide example implementations in a few popular frameworks (like Django, Laravel, Spring Boot)?
It can make the content even more practical!