StackOverflow Error - JPA Entity with HashMap

I want to make a little production calculator. I have a Part A which need 7s and its made out of x Part B which need 3s and y Part C which need 2s. Part C is made out of n Part D. So I have a recursion in Class Part and and its number of usage as "recipe". My Enitity Class

@Entity  @Data  public class ProductEntity {      @Id      @GeneratedValue(strategy = GenerationType.IDENTITY)      private Long id;      @Column(unique=true)      private String name;      private double productionCycleTimeInSeconds;      private int batchPerProductionCycle;        @Enumerated(EnumType.ORDINAL)      private FacilityEnum facility;        @ElementCollection      @JoinTable(name = "end_product_recipe", joinColumns = @JoinColumn(name = "end_product_id"))      @MapKeyColumn(name = "resourceId")      @Column(name = "usage_count")      private Map<ProductEntity, Integer> recipe;  }  

For Testing I wanted to init the table with 3 basics

        ProductEntity ironOre = new ProductEntity();          ironOre.setFacility(FacilityEnum.MINING_MACHINE);          ironOre.setName("Iron Ore");          ironOre.setProductionCycleTimeInSeconds(1.0);          ironOre.setBatchPerProductionCycle(1);          productRepository.save(ironOre);            ProductEntity ironIngot = new ProductEntity();          ironIngot.setFacility(FacilityEnum.SMELTER);          ironIngot.setName("Iron Ingot");          ironIngot.setProductionCycleTimeInSeconds(1.0);          ironIngot.setBatchPerProductionCycle(1);          Map<ProductEntity, Integer> recipe = new HashMap<>();          recipe.put(ironOre, 1);          ironIngot.setRecipe(recipe);          productRepository.save(ironIngot);            ProductEntity gear = new ProductEntity();          gear.setFacility(FacilityEnum.ASSEMBLING_MACHINE);          gear.setName("Gear");          gear.setProductionCycleTimeInSeconds(1.0);          gear.setBatchPerProductionCycle(1);          recipe.clear();          recipe.put(ironIngot, 1);          gear.setRecipe(recipe);          productRepository.save(gear);  

When Code get to last line (productRepository.save(gear);) i get Error:

java.lang.StackOverflowError      at java.util.HashMap$HashIterator.<init>(HashMap.java:1427)      at java.util.HashMap$EntryIterator.<init>(HashMap.java:1477)      at java.util.HashMap$EntrySet.iterator(HashMap.java:1014)      at java.util.AbstractMap.hashCode(AbstractMap.java:528)      at org.hibernate.collection.internal.PersistentMap.hashCode(PersistentMap.java:574)      at com.hoernerice.dspcalculator.entity.ProductEntity.hashCode(ProductEntity.java:12)      at java.util.Objects.hashCode(Objects.java:98)      at java.util.HashMap$Node.hashCode(HashMap.java:297)      at java.util.AbstractMap.hashCode(AbstractMap.java:530)      at org.hibernate.collection.internal.PersistentMap.hashCode(PersistentMap.java:574)      at com.hoernerice.dspcalculator.entity.ProductEntity.hashCode(ProductEntity.java:12)      at java.util.Objects.hashCode(Objects.java:98)      at java.util.HashMap$Node.hashCode(HashMap.java:297)      at java.util.AbstractMap.hashCode(AbstractMap.java:530)      at org.hibernate.collection.internal.PersistentMap.hashCode(PersistentMap.java:574)      at com.hoernerice.dspcalculator.entity.ProductEntity.hashCode(ProductEntity.java:12)      at java.util.Objects.hashCode(Objects.java:98)      at java.util.HashMap$Node.hashCode(HashMap.java:297)      at java.util.AbstractMap.hashCode(AbstractMap.java:530)      at org.hibernate.collection.internal.PersistentMap.hashCode(PersistentMap.java:574)      at com.hoernerice.dspcalculator.entity.ProductEntity.hashCode(ProductEntity.java:12)  ....  

it repeats so i guess i have an endless loop. but how? where is my mistake? For the first 2 items i have the rows as accepted in database. in the join table are "just" ids as wanted. So that work as accepted

sloved by replacing recipe.clear; with recipe = new HashMap<>();

https://stackoverflow.com/questions/66020805/stackoverflow-error-jpa-entity-with-hashmap-entity-integer February 03, 2021 at 11:25AM