hibernate-mapping.md

Types of Mapping

@OneToOne - One Product is owned by one member

• It's always a best practice to put mapping in PK class who owns and has FK mapping of owned entity.

@OneToOne
private Members members;

@OneToMany(One Member can own multiple Products)

• This mapping loads lazily by default hence leading to optimizing the performance. How? Say we have 50 members, with 100000 products. Each time, we need 1 member, entire product will be loaded for this operation. So, better load products only when required. Thats's lazy loading.
• Optional relationship type

@ManyToOne(Not used here but eg. Many Products owned by One Member)

• Eager by default. So, don't go for this unless required.
• @ManyToOne(fetch = FetchType.LAZY) - This again makes it lazy. But with same example as above, would you want to load entire 100000 products and work in the reverse way? No? Right, choice is yours.
• This relationship type is also optional by default but can be made mandatory - @ManyToOne(optional = false)
• If relationship type is mandatory, we can't save Member without a Product.

@ManyToMany(One member can read multiple books. And one book can be read by multiple members)

• Configurations for optionality, fetch type, cascading effect can be done as in others

Common Tips

• referencedColumnName isn't required for PK mapping. For non-PK mapping, it is required