QueryFence is an open-source library for Java that helps detect SQL queries that may lead to data leaks between tenants during the integration testing process, before the code is deployed to production.

THE PROBLEM

In multi-tenant SaaS applications that share a database, each customer's data is often separated by a tenant_id column. A single query that forgets this condition can inadvertently allow a customer to access another customer's data.

This error is very difficult to detect during code reviews, especially when SQL is automatically generated by Hibernate, JPA, or Spring Data. Integration tests can still succeed even if the SQL does not ensure tenant isolation.

KEY FEATURES

1. Automatically records the actual SQL queries executed during integration tests and checks them against policies defined in YAML.
2. Detects queries that lack the tenant_id condition, OR conditions that disable tenant scope, unsafe JOINs, findById that only filters by primary key, and UPDATE or DELETE statements that lack a WHERE clause.
3. Provides detailed error reporting with table names, SQL queries, class, method, and line of code that generated the query, helping developers quickly identify the cause.
4. Applies a fail-closed principle: SQL queries that cannot be analyzed are reported as errors rather than quietly ignored.
5. Supports REPORT Mode to gradually integrate into existing projects without causing immediate CI build failures.

HOW TO USE

QueryFence supports Java 17+, JUnit 5, Maven, Gradle, Spring Boot, Hibernate/JPA, MyBatis, and JdbcTemplate on PostgreSQL and MySQL.

Simply add the dependency com.steelreed:queryfence-spring-test:0.1.0 with scope test, create the file src/test/resources/queryfence.yml to declare the tables that need protection, and then run the integration tests as usual.

No need to modify test code or add annotations.

DIFFERENCE

Unlike static analysis tools that only analyze source code, QueryFence checks the actual SQL queries executed by the application, including SQL generated automatically by ORM.

QueryFence does not replace Row-Level Security or Hibernate Filters but adds an additional layer of checks in CI, helping to early detect risks of lacking tenant isolation.

QUALITY AND TESTING

The project is developed with the support of AI, but I have directly reviewed and tested it thoroughly through 260 standard test cases, mutation testing, and experiments on real applications to assess the error detection capability and false positive rates.

The goal of QueryFence is to help Java Backend teams build safer multi-tenant SaaS applications, reduce the risk of data leaks between customers, and detect errors early in the development phase rather than waiting until production.