A property management app for UK landlords: properties, tenants with UK checks, leases and a live dashboard. I built it alone over 7 months.
EstateLink keeps a landlord's properties, tenants and leases in one place, and checks tenants against UK lettings rules such as right to rent.
The interesting part is underneath. Moving a tenant into a property changes more than one record, so it runs as a single database transaction that lands completely or not at all.
There's no live link and no app screenshot on this page, and I won't draw a fake one. The diagram at the top is what one assignment does on the server. Further down I say what isn't finished.
Landlords, and the people who manage property for them. One might have a single house; another a block of flats with a different tenant and rent in every unit.
Letting in the UK comes with its own paperwork: right to rent, National Insurance numbers, referencing, guarantors. EstateLink models those as real fields instead of leaving them to a notes box. The tenant model alone runs to 1,585 lines.Source: server/models/Tenant.js (line count from wc -l)
Moving a tenant in isn't one write. The tenant record has to point at the property, and the property (or the flat inside it) has to point back at the tenant. If the server falls over between those two writes, you get a tenant who thinks they live somewhere that has never heard of them.
So each assignment runs inside a MongoDB transaction. The server opens a session, runs its checks, makes the writes, and only then commits. If anything throws on the way, it aborts, and the database looks exactly as it did before. Assigning, unassigning and the lease operations all work like this: four transactions in all.Source: server/services/tenantAssignmentService.js, lines 23 to 111, 128 to 193, 208 to 272 and 287 to 356
A middleware also runs a consistency check before the request reaches the service at all.Source: server/middleware/tenantConsistencyMiddleware.js, lines 14 to 60
Each landlord's dashboard keeps a Socket.IO connection open. The server checks their login token (a JWT) during the handshake before it will talk. When a tenant is assigned, it recomputes that landlord's numbers and pushes them only to that landlord's sockets, so nobody sees anyone else's portfolio.Source: server/server.js, lines 160 to 260; server/services/realTimeAnalytics.js, lines 20 to 45
That push happens after the commit, outside the transaction. Why that matters is the decision further down.
Reads go through Redis first, cached for 5 minutes, 15 minutes, 1 hour or 24 hours depending on the data, with keys split per user. Changing a property clears its entries. If Redis errors, the request goes straight to MongoDB instead of failing.Source: server/utils/cache.js, lines 7 to 60; server/controllers/propertyController.js
The server checks the file first, gives up reading its metadata after 10 seconds, and rejects anything over 10,000 pixels. Then sharp makes four WebP versions at quality 80: 300 by 200, 800 by 600, 1200 by 900, and 1920 wide. Abandoned uploads in a temp folder are cleared every 24 hours.Source: server/utils/imageProcessor.js, lines 5 to 60; server/utils/scheduledTasks.js, lines 20 to 40
Helmet with a content security policy, a limit of 100 requests per 15 minutes and 20 for writes, a separate upload limit, an origin check against cross-site request forgery on anything that changes data, NoSQL-injection sanitising and a 10 MB cap on request bodies.Source: server/server.js, lines 54 to 122; server/middleware/rateLimitMiddleware.js; server/middleware/csrfMiddleware.js
One of the server test files is for the assignment service itself, where the transactions live. Others cover auth, properties, tenants, the validators and the live analytics.Source: server/tests/ (tenantAssignmentService, realTimeAnalytics and seven more)
On every push and pull request to main, GitHub Actions lints the server and the client, runs the server tests and builds the client.Source: .github/workflows/ci.yml
I don't have a coverage figure I'd trust, so there isn't one here.
Pushing fresh numbers to the dashboard could have gone inside the transaction. I put it after the commit instead. A websocket can drop at any moment, and if the push sat inside the transaction, a dropped connection could roll back a perfectly good tenant assignment.
The cost: if a push fails, the dashboard is a step behind until it refreshes or reconnects, which the client does on its own. A stale chart is annoying. A half-assigned tenant is a mess to untangle.Source: server/services/tenantAssignmentService.js, lines 93 to 101; client/src/hooks/useRealTimeAnalytics.ts, lines 74 to 115
The cache follows the same rule. Redis makes reads faster, but if it goes down the app reads from MongoDB, and the health check reports "Redis not connected" instead of falling over.Source: server/utils/cache.js; server/routes/healthRoutes.js, lines 19 to 25
If I picked it back up, the first jobs would be: run the client tests in CI, take the placeholder stats down, and either build rent collection or stop promising it.
EstateLink's chunks are ringed and numbered. The dimmed points around them are the rest of that corner of my index.