Executing Simple Joins Across Owned Relationships for gae: http://gae-java-persistence.blogspot.com/2010/03/executing-simple-joins-across-owned.html
honzeland 2010-08-20 13:01 å‘表评论
]]>@Entity
@Table(name = "table_a")
public class A {
private Set<BlankField> blankFields = new HashSet<BlankField>();
@CollectionOfElements
@Fetch(FetchMode.SUBSELECT)
@Enumerated(EnumType.ORDINAL)
@JoinTable(name = "blank_fields", joinColumns = { @JoinColumn(name = "ref_id") })
@Cascade(value = org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
@Column(name = "blank_field", nullable = false)
@SQLInsert(sql = "INSERT INTO blank_fields(ref_id, blank_field, type) VALUES(?,?,0)")
@Where(clause = "type=0")
public Set<BlankField> getBlankFields() { // BlankField is an enum
return blankFields;
}
@SuppressWarnings("unused")
private void setBlankFields(Set<BlankField> blankFields) {
this.blankFields = blankFields;
}
} // End B
@Entity
@Table(name = "table_b")
public class B {
private Set<BlankField> blankFields = new HashSet<BlankField>();
@CollectionOfElements
@Fetch(FetchMode.SUBSELECT)
@Enumerated(EnumType.ORDINAL)
@JoinTable(name = "blank_fields", joinColumns = { @JoinColumn(name = "ref_id") })
@Cascade(value = org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
@Column(name = "blank_field", nullable = false)
@SQLInsert(sql = "INSERT INTO blank_fields(ref_id, blank_field, type) VALUES(?,?,1)") // used for insert
@Where(clause = "type=1") // used for query, if not @CollectionOfElements, such as @OneToMany, use @WhereJoinTable instead
public Set<BlankField> getBlankFields() {
return blankFields;
}
@SuppressWarnings("unused")
private void setBlankFields(Set<BlankField> blankFields) {
this.blankFields = blankFields;
}
}
当然˜q˜æœ‰å…¶ä»–çš„æ–¹å¼æ¥å®žçŽ°ä¸Šé¢çš„需求，上é¢é‡‡ç”¨çš„å•è¡¨æ¥è®°å½•ä¸åŒå®žä½“çš„associationsåQˆè¿™å„¿æ˜¯CollectionOfElementsåQŒåƈ且返回的是Set<Enum>åQŒä¸æ˜¯Set<Embeddable>)åQŒç„¶åŽç”¨'type'æ¥åŒºåˆ†ä¸åŒçš„实体åQŒè¿™æ ·åšçš„好处是åQšæ•°æ®åº“冗余ž®‘，易于扩展åQŒå¯¹äºŽæ–°çš„实体，åªéœ€åŠ 一个typeå€û|¼Œè€Œä¸éœ€æ›´æ”¹æ•°æ®åº“表¾l“构。å¦å¤–一¿U采用å•è¡¨çš„æ–¹å¼æ˜¯äØ“(f¨´)æ¯ä¸ªå®žä½“å¢žåŠ æ–°çš„å—段åQŒå¦‚"blank_fields": 'a_id', 'b_id', 'blank_field', a_id reference table_a (id), b_id reference table_b (id). ˜q™æ ·åœ¨æ˜ ž®„的时候更½Ž€å•ï¼Œ
对于AåQŒæ˜ ž®„äØ“(f¨´)
@JoinTable(name = "blank_fields", joinColumns = { @JoinColumn(name = "a_id") })
对于BåQŒæ˜ ž®„äØ“(f¨´)
@JoinTable(name = "blank_fields", joinColumns = { @JoinColumn(name = "b_id") })
˜q™æ ·ä½œçš„¾~ºç‚¹æ˜¯ï¼š(x¨¬)带æ¥äº†æ•°æ®åº“冗余åQŒå¯¹äº?span style="color: #000000;">blank_fieldsæ¥è®²åQŒä“Q一æ¡è®°å½•ï¼Œa_idå’Œb_idä¸åªæœ‰ä¸€ä¸ªä¸ä¸ºnull。当多个实体å…Þq”¨˜q™ä¸ªè¡¨æ—¶åQŒç”¨ä¸Šé¢çš„方法更åˆç†åQŒå¦‚果共用实体ä¸å¤šæ—¶åQŒè¿™¿U方法更方便ã€?/span>
honzeland 2010-04-20 17:20 å‘表评论
]]>i.e., open multiple transactions on the same session, even though one transaction rolls back, other transactions can be committed. If one action fails, others should fail too, then we should use one transaction for all actions.
Note:
A rollback with a single Session will lead to that Session being cleared (through "Session.clear()").
So do lazy collections still work if the session is cleared? =>Not of any objects that you loaded up until the rollback. Only for new objects loaded afterwards.
We should load necessary objects to session for each transactional action to avoid LazyInitializationException, even if those objects are loaded before other forward transactional actions, since forward action may be rolled back and clear the session.
BTW, Hibernate Session.merge() is different with Session.update() by:
Item item2 = session.merge(item);
item2 == item; // false, item - DETACHED, item2 - PERSIST
session.update(item); // no return value, make item PERSIST
item2 == item; // false, item - DETACHED, item2 - PERSIST
session.update(item); // no return value, make item PERSIST
honzeland 2010-03-01 11:47 å‘表评论
]]> @Transactional
public void foo() {
try{
bar();
} catch (RuntimeException re) {
// caught but not throw further
}
}
@Transactional
public void bar() {
}
如果foo在调用bar的时候，bar抛出RuntimeExceptionåQŒSpring在bar return时将Transactionalæ ‡è®°ä¸ºRollback onlyåQ?而fooæ•èŽ·äº†barçš„RuntimeExceptionåQŒæ‰€ä»¥Springž®†ä¼š(x¨¬)commit foo的事务，但是fooå’Œbar使用的是åŒä¸€äº‹åŠ¡åQŒå› æ¤åœ¨commit foo事务æ—Óž¼Œž®†ä¼š(x¨¬)抛出UnexpectedRollbackException。注æ„：(x¨¬)如果fooå’Œbar在åŒä¸€classä¸ï¼Œä¸ä¼š(x¨¬)出现˜q™ç§æƒ…况åQŒå› 为：(x¨¬)public void foo() {
try{
bar();
} catch (RuntimeException re) {
// caught but not throw further
}
}
@Transactional
public void bar() {
}
Since this mechanism is based on proxies, only 'external' method calls coming in through the proxy will be intercepted. This means that 'self-invocation', i.e. a method within the target object calling some other method of the target object, won't lead to an actual transaction at runtime even if the invoked method is marked with @Transactional!
å¯ä»¥é€šè¿‡é…ç½®log4jæ¥debug Spring事务获å–情况åQ?br /> To delve more into it I would turn up your log4j logging to debug and also look at what ExerciseModuleController is doing at line 91, e.g.: add a logger for org.springframework.transaction
honzeland 2010-02-24 18:02 å‘表评论
]]>honzeland 2010-01-29 17:20 å‘表评论
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