Simple hospital API made with NestJS and DynamoDB

Simple hospital API made to demonstrate DynamoDB capabilities.

Things demonstrated

• DynamoDB data modeling
  • Single Table Design
  • One-to-many relationships
  • Many-to-many relationships
  • Cross-partition querying
  • Pagination and Sorting strategies
  • Singleton strategy
  • Incomplete migration helper and some more interesting stuff :)
• NestJS
• Vertical slice architecture
• CQS

Running locally

Prerequisites: This example requires only node and docker installed.

ERD

A very simple ERD was used for this project. However, it was more than enough to demonstrate a lot of different DynamoDB concepts based on the access patterns.

Entities

Initial entities included:

• Doctor
• Patient
• Test

which was obvious from the ERD. As different access patterns were modeled two more entities were added:

• DoctorPatient - to address many-to-many relationship between Doctors and Patients
• Specialization - singleton that has a set of all medical departments in a hospital

Entity chart

Entity chart is used to keep track of all the different item types that we are going to store in our table.

ENTITY	PK	SK
Patient	PATIENT#<PatientId>	PATIENT#<PatientId>
Doctor	DOCTOR#<DoctorId>	DOCTOR#<DoctorId>
Test	PATIENT#<PatientId>	#TEST#<KSUID>
Specialization	DOCTOR	SPECIALIZATION
DoctorPatient	DOCTOR#<DoctorId>	PATIENT#<PatientId>

Access patterns

ENTITY	ACCESS PATTERN	INDEX	PARAMS	NOTES
Patient	Get	/	pk: PATIENT#<PatientId> sk: PATIENT#<PatientId>	/
	List - sort by created time	GSI2	pk: PATIENT#<TRUNC_TO_WEEK(CreatedAt)> sk: PATIENT#<CreatedAt>	We get 100 new patients weekly
	List - sort by lastname	GSI1	pk: PATIENT#<TRUNC(LastName)> sk: PATIENT#<LastName-CreatedAt>	/
	Create	/	pk: PATIENT#<PatientId> sk: PATIENT#<PatientId>	/
	Update	/	pk: PATIENT#<PatientId> sk: PATIENT#<PatientId>	/
	Delete	/	pk: PATIENT#<PatientId> sk: PATIENT#<PatientId>	/
	List of Patients for a specific Doctor	GSI3	pk: PATIENT#<PatientId> sk: DOCTOR#<DoctorId>	/
Doctor	Get	/	pk: DOCTOR#<DoctorId> sk: DOCTOR#<Specialization>	/
	List - sort and filter by specialization	GSI2	pk: SPECIALIZATION#<Specialization> sk: <Specialization>#<DoctorId>	Cross-partition query of doctors. Sort in order of alphabetically sorted specializations.
	Create	/	pk: DOCTOR#<DoctorId> sk: DOCTOR#<DoctorId>	/
	Update	/	pk: DOCTOR#<DoctorId> sk: DOCTOR#<DoctorId>	/
	Delete	/	pk: DOCTOR#<DoctorId> sk: DOCTOR#<DoctorId>	/
	List Doctors for specific Patient	GSI3	pk: PATIENT#<PatientId> sk: DOCTOR#<DoctorId>	/
Test	Get test for patient	/	pk: PATIENT#<PatientId> sk: #TEST#<KSUID>	/
	Create test for patient	/	pk: PATIENT#<PatientId> sk: #TEST#<KSUID>	/
	List tests for patient	/	pk: PATIENT#<PatientId> sk: #TEST#<KSUID>	/
	List tests performed by specific doctor	GSI1	pk: DOCTOR#<DoctorId> sk: #TEST#<KSUID>	GSI1 is added to both doctors and tests
Specialization	Get	/	pk: DOCTOR sk: SPECIALIZATION	Specialization is a singleton item that has a set of all possible specializations in a hospital
	Add new	/	pk: DOCTOR sk: SPECIALIZATION	Adding simply adds to the singleton's set
DoctorPatient	Assign Doctor to Patient	/	pk: DOCTOR#<DoctorId> sk: PATIENT#<PatientId>	Many-to-many rel for doctors and patients, uses GSI3
	Remove patient from doctor	/	pk: DOCTOR#<DoctorId> sk: PATIENT#<PatientId>	/

GSI1 TABLE

ENTITY	GSI1PK	GSI1SK
Doctor	DOCTOR#<DoctorId>	DOCTOR#<DoctorId>
Test	DOCTOR#<DoctorId>	#TEST#<KSUID>
Patient	PATIENT#<TRUNC(LastName)>	PATIENT#LAST_NAME)>

GSI2 TABLE

ENTITY	GSI2PK	GSI2SK
Patient	PATIENT#<TRUNC(WEEK)>	PATIENT#CREATED_AT
Doctor	SPECIALIZATION#<Specialization>	<Specialization>#<DoctorId>

GSI3 TABLE

ENTITY	GSI3PK	GSI3SK
Patient	DOCTOR#<DoctorId>	PATIENT#<PatientId>
Doctor	PATIENT#<PatientId>	DOCTOR#<DoctorId>

Things left to be done

• Move DynamoDB creds to .env
• [] Implement result pattern
• [] Export postman collection
• [] Add tests
• [] Add seed script
• [] Add API documentation
• [] Dockerize app w/ db