Not supported for DML operations with JPA update query

As far as I understand, you should not use @Transactional annotation in the repository class. Find the below answer.

Service Impl class

import org.springframework.transaction.annotation.Transactional;
...
@Test
@Transactional
public void updateMaterialInventory() throws Exception{

    // Initialize the database
    materialRepository.saveAndFlush(material);

    long id =  material.getId();
    materialRepository.updateMaterialInventory(id,UPDATED_INVENTORY_COUNT);

    assertEquals(material.getInventory_count(), UPDATED_INVENTORY_COUNT, 0);
}

Repository class

import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
...

  @Modifying
  @Query("UPDATE Material m SET m.inventory_count = ?2 WHERE m.id = ?1")
  void updateMaterialInventory(Long id,int newInventoryAmount);

make sure to use the correct imports. hope this is helpful.

The @Modifying annotation must be placed on the updateMaterialInventory method, along to the @Query annotation, to let Spring-data know that the query is not a query used to select values, but to update values.