[OPENJPA-2299] N+1 select when eager fetching two collection fields of the same entity type

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.2.1, 2.3.0
• Component/s: jdbc, jpa, performance
• Assignee: Unassigned
• Reporter: Vermeulen
• Created: 21/Nov/12 12:56
• Updated: 21/Jul/14 08:07

Description

I have a ProductOrder entity that has two @OneToMany lists of ProductOrderLines. When selecting from ProductOrder, eager fetching does not seem to recurse into the second list so that each field of each ProductOrderLine in the second list is fetched using a separate "load field" operation.

The problem does not occur when there is only one List.

@Entity
public class ProductOrder {
@JoinColumn(name = "PLANNED_ORDER_ID")
@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<ProductOrderLine> plannedOrderLines = new ArrayList<ProductOrderLine>();

@JoinColumn(name = "ACTUAL_ORDER_ID")
@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<ProductOrderLine> actualOrderLines = new ArrayList<ProductOrderLine>();

Expected nr of queries: 1 (for Order) + 1 (for Order.plannedOrderLines) + 1 (for Order.actualOrderLines).
Actual nr of queries: same as expected + 1 query for each field of each ProductOrderLine in Order.actualOrderLines.

Same problem exists when using @JoinTable instead of @JoinColumn (JPA 2.0 only).