Hibernate urgent left outer connection and urgent inner connection

• Urgent LEFT outer connection: left JOIN FETCH keyword indicates an urgent left OUTER join retrieval policy. The –list () method returns a reference to the collection that holds the entity object, and the employee collection associated with each Department object is initialized to hold all the entity objects of the associated employee. – The query results may contain duplicate elements that can be filtered by a HashSet. • LEFT OUTER join: The –left JOIN keyword represents a left outer join query. The collection returned by the –list () method is an object array type – A retrieval policy that determines the Employee collection based on the configuration file.

If you want the list () method to return a collection that contains only Department objects, you can use the SELECT keyword in a hql query statement

• Urgent internal connection: –inner Join the FETCH keyword indicates an urgent inner join, or you can omit a reference to the Department object in the collection returned by the INNER keyword –list () method, and the Employee collection for each Department object is Initialize, hold all associated Employee objects • Internal connection: –inner Join keyword indicates an inner join, or you can omit the INNER keyword –list () method that contains a record of each element in the collection that corresponds to the query result, each element is an object array type-if you want to The returned collection of the list () method contains only the Department object, and you can use the SELECT keyword in a HQL query statement