Inventory Management System
A data-focused build: stock levels, movements, concurrency and reporting that must stay correct under simultaneous use.
Technologies
The brief
What the finished thing needs to do.
- Products with stock levels across multiple locations
- Record stock movements: receipts, issues and transfers
- Current stock derived from movement history, not stored as a mutable number
- Prevent stock going negative
- Handle two users moving the same stock simultaneously
- Reports: stock on hand, movement history, items below reorder level
How to structure it
The key design decision is that stock level is derived from an immutable movement history rather than held as a number that gets updated. That gives you a full audit trail and removes a whole class of concurrency bug.
It also introduces a real problem: calculating current stock by summing all history becomes slow as the history grows. Solving that properly — with a periodic snapshot, or a maintained running balance — is the most valuable part of this project.
Concurrency is unavoidable here. Two simultaneous issues of the last item in stock must not both succeed, which means a transaction and a deliberate isolation choice.
Why these technologies
- Immutable movement records
- Gives an audit trail and makes stock a calculated value rather than contested mutable state.
- Database transactions
- Checking availability and recording an issue must be atomic.
- Indexes on product and location
- Movement history grows quickly and every report filters on these.
Build it in this order
Each stage produces something that works. That matters — a project that only runs at the very end is a project people abandon.
Products and locations
Schema and basic CRUD.
Movement records
Receipts and issues as immutable rows with a type, quantity and timestamp.
Calculate stock on hand
Aggregate movements per product and location.
Prevent negative stock
Check availability inside the same transaction as the write.
Transfers
Two movements that must both succeed or both fail.
Concurrency
Simulate two simultaneous issues and confirm only one succeeds.
Reports
Stock on hand, history, and items below reorder level.
Performance
Add indexes, examine the execution plans, and address the growing-history problem.
Done means
How to know it is finished
Check each of these before moving on. If one fails, the project is not done yet — and that is useful information rather than a setback.
- Stock on hand always equals the sum of movements
- Stock cannot be driven negative, including under simultaneous requests
- A transfer never leaves stock in only one location
- Reports return correct figures and remain acceptably fast as history grows
- Every report query uses an index, confirmed from the execution plan
If you want to go further
Extensions worth attempting
Only once the core build meets every criterion above.
- Add batch or serial number tracking
- Add stock valuation using a costing method
- Add periodic snapshots to bound the aggregation cost
- Add a reservation concept for stock allocated but not yet issued
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