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Phase 5 — Backend Logic

This phase documents how the backend connects the frontend to the MySQL schema implemented in Phase 4.

Basic SQL Queries Frontend Interface

1. Backend Role

The backend is the application layer between UI and database:

  • Receives HTTP requests
  • Validates inputs
  • Executes parameterized SQL
  • Returns structured responses
  • Enforces business and integrity rules

2. Module Structure

2.1 Routes / Controllers

  • Expose endpoints (users, family members, medical data, alerts, appointments, content)
  • Map request/response handling

2.2 Service / Business Logic

  • Input rule checks
  • Ownership checks (user-scoped data)
  • Workflow decisions (for example alert status transitions)

2.3 Data Access Layer

  • Connection pooling
  • Parameterized query execution
  • Transaction handling for multi-step operations

2.4 Validation and Error Handling

  • Required field validation
  • ENUM/domain validation before query execution
  • Consistent error responses for FK/UNIQUE/CHECK violations

3. CRUD Coverage by Domain

  • User: create profile, read account, update contact data
  • FamilyMember: full CRUD (scoped to owner)
  • MedicalHistory: full CRUD with required member/condition links
  • HealthEvent: event logging with optional member/condition references
  • RiskAlert: list/update status (New, Viewed, Resolved)
  • Clinic: read catalog data
  • Appointment: create/list/update status/cancel
  • AwarenessContent: read for users, write/update/delete for admin roles

4. Constraint-Aware Backend Behavior

Backend logic is aligned with database constraints:

  • Handles UNIQUE errors (for example duplicate User.email)
  • Prevents invalid ENUM values before SQL execution
  • Surfaces FK dependency issues clearly (RESTRICT relationships)
  • Supports cascade-aware deletion flows (CASCADE relationships)
  • Validates date/range fields that map to CHECK constraints

5. Security and Reliability

  • Parameterized queries to prevent SQL injection
  • Input sanitization and schema-level validation
  • Role-based authorization for privileged operations
  • Structured logging for requests, query failures, and constraint violations

Backend Outcome

The backend design provides clean separation of concerns and reliable execution of schema-aware operations for all major application features.