How to make hierarhical mapping Hibernate?
For example: Category
id parent_id name
1 0 Root
2 1 Sub-root 1
3 1 Sub-root 2
4 2 Sub-(sub-root 1)
Is it possible to make lazy mapping for such Category object?
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2 Answers
It is not exactly clear what you are asking.
However it would appear you are talking about a self-referencing relationship rather than Inheritance so you can then map as below. The default fetch strategy should be same as for any other @OneToMany i.e. LAZY.
@Entity
public class Category{
@Id
private Long id;
@ManyToOne
@JoinColumn(name = "parent_id")
private Category parent;
@OneToMany(mappedBy = "parent")
private Set<Category> subCategories;
}
Comments
I believe you want to ask about inheritance of entities. I recommend using JPA inheritance strategies. There are 3 available.
- Single Table: Uses only one database table. columns need to be nullable and hence wastes database space
- Joined Strategy: Uses multiple table which can be joined for insertion and retrieval of entity data. Saves database space but performance becomes an issue when inheritance hierarchy becomes wide and deep
- Table per concrete class: Uses separate database tables which are not joined.
Different strategies have different advantages and disadvantages. You can choose according to your need.
