#508

Multi-tenant

One database, many companies. Hibernate adds the tenant filter to every query for you.

Technique: Hibernate @TenantId + CurrentTenantIdentifierResolver + sub-domain / session resolution

Read the code: src/main/java/com/study/advlab/core/TenantFilter.javasrc/main/java/com/study/advlab/core/TenantIdentifierResolver.javasrc/main/java/com/study/advlab/tenancy/TenantService.java

This request

Northwind Electronics

tenant_id = 1 · code northwind

Found by: Signed-in user "nina.admin" (session)

Open a company by its sub-domain (no DNS needed - browsers send *.localhost to this PC):

http://northwind.localhost:80/http://siamsport.localhost:80/http://blueharbor.localhost:80/

Proof that the data is isolated

`productRepository.count()` JPA, @TenantId	41
`SELECT COUNT(*) FROM product WHERE tenant_id = ?`	41
`SELECT COUNT(*) FROM product` native, no filter	110
`productRepository.findById(42)` - a product of Siam Sport & Outdoor	empty

The repository methods have no tenant parameter. Hibernate adds where tenant_id = ? to every query of an entity with @TenantId, and fills tenant_id on insert.

Native SQL (JdbcTemplate) is not filtered - every hand-written query in this project passes tenant_id = ? itself. Forgetting it is the classic multi-tenant bug.

Companies rows per table - native SQL, like a database admin sees it

Company	Users	product	customer	purchase	review	txn	kb_article	lead	face_person	experiment	geo_zone	chat_message	Plan	Status
Northwind Electronics id 1 · northwind		0	0	0	0	0	0	0	0	0	0	0
Siam Sport & Outdoor id 2 · siamsport		0	0	0	0	0	0	0	0	0	0	0
Blue Harbor Home id 3 · blueharbor		0	0	0	0	0	0	0	0	0	0	0

Three ways to do multi-tenancy

Approach	Isolation	Cost
Shared tables + tenant_id (this lab)	by code - filter every query	cheapest, easiest to run
Schema per tenant	by database schema	medium, migrations × N
Database per tenant	strongest, own backups	most expensive

SQL Server can add a safety net with Row-Level Security (a security policy on tenant_id), so even a forgotten WHERE cannot leak.