Every time we read a value from the database, a copy is stored in memory which is later used for dirty checking the entity. If we read too many values from the database without needing all of them, then we may run into OutOfMemoryException. This is why a good practice is to mark our session as read only if we plan on reading entities not for modifying them. This will tell Hibernate that once we are done, there is no reason for dirty checking as a result no copy of the entity needs to be done in the persistence context cache. We need to be very careful with collections and dirty checking. Always use property annotation on collection mappings. Otherwise, the dirty checking may consider the collection as modified and the result will be that all associated entities will be deleted and re-inserted.
Hibernate is offering a configuration called LazyCollectionOption.EXTRA. Extra lazy collections means we can apply trivial operations to them without having to retrieve them from the database and without having to write these trivial queries to avoid doing so. Trivial operations are considered the size(), isEmpty() and contains(). If for example we have an entity User and an extra lazy collection called Address we can call user.getAddress.size() and this will generate a COUNT query on the ADDRESS table. So, no need to write a special query or load in memory the collection. Lazy loading is set by default to @OneToMany relations but you need to set it on @ManyToOne which are by default Eagerly loaded. @OneToOne can be lazy loaded only if the relation is not optional. If the relation is optional the the proxy will have to query the database to find out if it should be null or if it should be initiated. A spring boot property that needs to be overriden in all our applica...
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