Hello,

I am still somewhat new to Hibernate and trying to undrestand the fetch attribute of associations. I don't quite understand the implications of comibining fetch = "join|select" with lazy = "false|ture" and was hoping to get some guidance. I have four scenarios below with a sample mapping file -- would someone please help me understand what is going to happen in each case when using either of the following two queries:
(a) select compdeps from Compdep as compdeps
(b) select compdeps from Compdep as compdeps left join fetch compdeps.empdeps as empdeps



Case 1 (lazy = false, fetch = join): the "empdeps" set has lazy="false" and fetch="join".





Case 2 (lazy = true, fetch = join): the "empdeps" set has lazy="true" and fetch="join".





Case 3 (lazy = false, fetch = select): the "empdeps" set has lazy="false" and fetch="select".






Case 4 (lazy = true, fetch = select): the "empdeps" set has lazy="true" and fetch="select".

Hey mcburton3,

Let me put it this way:

Irrespective of the combination of usage of 'lazy' and 'fetch' attributes,
1 -> We use lazy to define a contract on how association is to be fetched on load of parent object.
2 -> We use fetch to tune performance.

To be more clear on point 2:
When fetch= join --> Hibernate retrieves the associated instance or collection in the same SELECT, using an OUTER JOIN.
When fetch=select --> a second SELECT is used to retrieve the associated entity or collection. Unless you explicitly disable lazy fetching by specifying lazy="false", this second select will only be executed when you access the association.