How to save Entity without affecting a related Entity

[Izanami Caster]

I'm using  to Spring Data with Hibernate and have run into an issue. .

There are 2 entities : Activity, Category

Activity   ---- One to Many --- Category

Problem / Need:

Assuming that a Category record already exists in the database, I want to save a given activity pertaining to a pre-existing category.

Using the method provided in the ActivityRunner class below doesn't work.  Please note that in this class, an attempt has been made to save off Activity alone, but  not save Category, because I want to use the existing category through a foreign key reference. However the code doesn't allow me to use a "transient" instance of Category. I hope I've made my problem clear. Can anyone help ?


Activity

@Entity(name = "ACTIVITY")
public class Activity {

	@Id
	@GeneratedValue(strategy = GenerationType.TABLE)
	private int id;
	@Column(name = "NAME", nullable = false, unique = true)
	private String name;
	@Column(name = "QUARTER")
	private Integer quarter;
	@ManyToOne(cascade = CascadeType.ALL)
	private Category category;
	@Column(name = "UNIT_DURATION")
	private Integer unitDuration;
	@Column(name = "UNIT_MEASUREMENT")
	private String unitMeasurement;
	@Column(name = "UNIT_WEIGHT")
	private Integer unitWeight;
	@Column(name = "BINARY_SUFFICIENCY")
	private Boolean binarySufficiency;
	@Column(name = "NO_DO_WEIGHT")
	private int noDoWeight;

	public Activity() {
		super();
		// TODO Auto-generated constructor stub
	}

	public Activity(String name, Category category, Integer unitDuration, String unitMeasurement,
			Boolean binarySufficiency) {
		super();

		this.name = name;
		this.category = category;
		this.unitDuration = unitDuration;
		this.unitMeasurement = unitMeasurement;
		this.binarySufficiency = binarySufficiency;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getQuarter() {
		return quarter;
	}

	public void setQuarter(Integer quarter) {
		this.quarter = quarter;
	}

	public Category getCategory() {
		return category;
	}

	public void setCategory(Category category) {
		this.category = category;
	}

	public Integer getUnitDuration() {
		return unitDuration;
	}

	public void setUnitDuration(Integer unitDuration) {
		this.unitDuration = unitDuration;
	}

	public String getUnitMeasurement() {
		return unitMeasurement;
	}

	public void setUnitMeasurement(String unitMeasurement) {
		this.unitMeasurement = unitMeasurement;
	}

	public Integer getUnitWeight() {
		return unitWeight;
	}

	public void setUnitWeight(Integer unitWeight) {
		this.unitWeight = unitWeight;
	}

	public Boolean getBinarySufficiency() {
		return binarySufficiency;
	}

	public void setBinarySufficiency(Boolean binarySufficiency) {
		this.binarySufficiency = binarySufficiency;
	}

	public int getNoDoWeight() {
		return noDoWeight;
	}

	public void setNoDoWeight(int noDoWeight) {
		this.noDoWeight = noDoWeight;
	}

	@Override
	public String toString() {
		return "Activity [id=" + id + ", name=" + name + ", quarter=" + quarter + ", category=" + category
				+ ", unitDuration=" + unitDuration + ", unitMeasurement=" + unitMeasurement + ", unitWeight="
				+ unitWeight + ", binarySufficiency=" + binarySufficiency + ", noDoWeight=" + noDoWeight + "]";
	}

}

Category:

@Entity(name = "CATEGORY")
public class Category {

	@Id
	@GeneratedValue(strategy = GenerationType.TABLE)
	@Column(name = "CATEGORYID")
	private int categoryId;
	
	@Column(name="CATEGORYNAME",nullable = false, unique = true)
	private String categoryName;
	
	

	public Category() {
		super();
		// TODO Auto-generated constructor stub
	}

	public Category(String categoryName) {
		super();
		this.categoryName = categoryName;
	}

	public int getCategoryId() {
		return categoryId;
	}

	public void setCategoryId(int categoryId) {
		this.categoryId = categoryId;
	}

	public String getCategoryName() {
		return categoryName;
	}

	public void setCategoryName(String categoryName) {
		this.categoryName = categoryName;
	}

}

An attempt to save Activity using crud repository.

@Component
public class ActivityRunner implements CommandLineRunner {

	@Autowired
	private ActivityRepository activityRepository;
	
	@Autowired
	private CategoryRepository categoryRepository;

	@Override
	public void run(String... args) throws Exception {
		// TODO Auto-generated method stub
		
		


		activityRepository.save(new Activity("Study", new Category("Academic"), 15, UnitOfMeasurement.MINUTE, false));

	}
}

[Rob Spoor]

The Category you use is a fresh new object. It has no id set, so Spring Data / JPA treats it as a new entity. It will therefore try to insert it. Whether or not that succeeds depends on your unique constraints.

What you need to do is use a CategoryRepository to find the Category by its name, then use the result in the Activity.


Note that we've had something similar recently in https://coderanch.com/t/745425/databases/ERROR-OneTOMany-ManyToOne-mapping-FK. There's one big difference though - there the linked record (in this case Category) was identified by its id, not a different field. I also don't see any methods on CrudRepository that lets you get a reference based on the id, only a full entity.

[Izanami Caster]

Thank you Rob!!

Your suggestion has worked. I'll put this down to my lack of knowledge of what the API provides.

To arrive at my solution I firstly removed the wrongly placed CascadeType.ALL on the ManyToOne relationship. Later I used the categoryRepository.findById to reference the "detached" entity.

@Component
public class ActivityRunner implements CommandLineRunner {

	@Autowired
	private ActivityRepository activityRepository;

	@Autowired
	private CategoryRepository categoryRepository;

	@Override
	public void run(String... args) throws Exception {
		// TODO Auto-generated method stub
		Optional<Category> categoryOptional = categoryRepository.findById(2L);
		Category category = categoryOptional.get();
		activityRepository.save(new Activity("Repeat", category, 15, UnitOfMeasurement.MINUTE, false));

	}
}

Thanks again for the guidance!!!
-Izanami Caster

[Rob Spoor]

You're welcome.