Assembler/Spring GraphQL Example

This repository showcases the standalone usage of Assembler + the integration of Assembler with Spring GraphQL to aggregate data from multiple sources in a single query. This combination serves as a powerful tool for implementing API composition, facilitating efficient data retrieval while reducing the complexity of client-side data aggregation.

Scenario

This example demonstrates a basic healthcare application for simulating monitoring patient data. Three services are implemented: the Patient Service for retrieving patient demographics from PostgreSQL, the Body Measurement Service for retrieving patient's height and weight from MongoDB, and the SpO2 Streaming Service for real-time oxygen saturation monitoring from a pulse oximeter device via Kafka. A GraphQL Controller is implemented in PatientObservationGraphQLController to aggregate data from these services.

This sample app was deliberately kept simple to showcase the Assembler/Spring GraphQL integration in a very accessible way. However, it does not incorporate more advanced concepts such as Change Data Capture (CDC) or complex stream processing. Additionally, it does not emphasize any distributed/scalability architecture patterns.

Assembler + Spring GraphQL for API Composition and solving the N+1 Query Problem

Batch Mapping (Data Querying)

The new BatchRule API from Assembler seamlessly integrates with the Spring GraphQL @BatchMapping mechanism, as shown in the usage example found in PatientObservationGraphQLController. Additionally, this example showcases additional features of Assembler, including:

• caching of service invocations using the cached() function
• caching of real-time data streams with the autoCache() function.

Subscription Mapping (Data Streaming)

Assembler excels in complex data aggregation within a data streaming scenario. This example demonstrates its usage in standalone mode in conjunction with Spring GraphQL using @SubscriptionMapping. By combining streaming and batching, Assembler enables seamless data stream augmentation for clients connected via WebSockets, offering an effective complement to GraphQL's native streaming support.

How to Run the Application

• Make sure Docker is installed
• Run the main method in src\test\java\io\github\pellse\example\PatientMonitoringApplicationTest.java
  • Or execute the bootTestRun Gradle Task

This repository takes advantage of the new Spring Boot 3.1.0 Testcontainers support for local development.

How to Use the Application

Open a browser at http://localhost:8080/graphiql?path=/graphql

For Batch Mapping (Data Querying)

• Run the following GraphQL Query:

{
  patientObservations: patients {
    name
    health_card_number: healthCardNumber
    body_measurement: bodyMeasurement {
      height_cm: height
      weight_kg: weight
      time
    }
    oxygen_saturation: spO2 {
      spO2Value
      time
    }
  }
}

Periodically rerun the query, the number of SpO2 values for each patient should increase:

For Subscription Mapping (Data Streaming)

• Run the following GraphQL Query:

subscription {
  spO2_reading: spO2Reading {
    oxygen_saturation: spO2 {
      id
      value_in_percentage: spO2Value
      time
    }
    patient {
      id
      name
      health_card_number: healthCardNumber
    }
    body_measurement: bodyMeasurement {
      height_cm: height
      weight_kg: weight
    }
  }
}

You should see the following:

SpO2.Readings.mp4

Tech Stack

• Assembler
• Spring GraphQL
• Spring Data
  • Reactive PostgreSQL (R2DBC)
  • Reactive MongoDB
• Spring Cloud Function
  • Spring Cloud Stream
    • Reactive Kafka
• Testcontainers