GraphQL + Hibernate Reactive + Spring

Re-produce the java.lang.IllegalStateException: Session/EntityManager is closed exception

Problem Statement

Given a Parent entity which has a one-many relationship with a Child entity, when multiple Parents exist, each with a child, then when a GraphQL query is made to fetch all Parents with their Children using the withSession method then a java.lang.IllegalStateException: Session/EntityManager is closed is thrown.

If the withSession is replaced by a withTransaction then the exception isn't thrown but this doesn't solve the underlying issue.

Env Setup

Database

Running the commands in src/main/resources/dbCreation.sh will pull a Docker Image of MySQL 5.7 and start a container. The username/password for this container are the same as in the application.yml

Creating the DB Schema

Use the SQL statements found in src/main/resources/schemaCreation.sql to create the schema and the tables.

This script also contains DML queries to create two Parent entities, each having a Child.

Alternatively, the API can be used to call the createData mutation to generate data in the database. For more information on how to run the server checkout the Server and API section.

Note: I can only reproduce the exception when there are at least two Parents and each Parent has at least one Child.

Tests

Tests which reproduce the issue can be found at src/test/kotlin/com/example/graphqlhibernatereactive/spec/ParentChildSpec. In order to run successfully the tests need to connect to a database with a valid schema.

Server and API

If the instructions above were used then the server should be able to boot without any errors. Execute ./gradlew :bootRun boot the server.

To call the API import src/main/resources/API.postman_collection.json into Postman.

Execute the withSession request. This request fetches all Parents and each their Children using GraphQL but fails to fetch the second Parent's Child.

Execute the withTransaction request. This query fetches the Children entities in a transaction. This query doesn't throw an exception.

This a simple example to reproduce the exception but using withTransaction is not a solution because I have a more complex data model in a private repo which throws other exceptions down the line if I try to fetch more deeply nested entities.

Expected Behaviour

All Parents and their Children are fetched successfully.

Actual Behavior

The first Parent and its Child is fetched successfully. The second Parent is also fetched successfully but an exception is throw while the API tries to fetch the second Parent's Child.