Object identity and equality return username.hashCode(); } } (Web hosting uk)
Object identity and equality return username.hashCode(); } } For some other classes, the business key may be more complex, consisting of a combination of properties. Here are some hints that should help you identify a business key in your classes: Consider what attributes users of your application will refer to when they have to identify an object (in the real world). How do users tell the difference between one object and another if they re displayed on the screen? This is probably the business key you re looking for. Every attribute that is immutable is probably a good candidate for the business key. Mutable attributes may be good candidates, if they re updated rarely or if you can control the situation when they re updated. Every attribute that has a UNIQUE database constraint is a good candidate for the business key. Remember that the precision of the business key has to be good enough to avoid overlaps. Any date or time-based attribute, such as the creation time of the record, is usually a good component of a business key. However, the accuracy of System.currentTimeMillis() depends on the virtual machine and operating system. Our recommended safety buffer is 50 milliseconds, which may not be accurate enough if the time-based property is the single attribute of a business key. You can use database identifiers as part of the business key. This seems to contradict our previous statements, but we aren t talking about the database identifier of the given class. You may be able to use the database identifier of an associated object. For example, a candidate business key for the Bid class is the identifier of the Item it was made for together with the bid amount. You may even have a unique constraint that represents this composite business key in the database schema. You can use the identifier value of the associated Item because it never changes during the lifecycle of a Bid setting an already persistent Item is required by the Bid constructor. If you follow our advice, you shouldn t have much difficulty finding a good business key for all your business classes. If you have a difficult case, try to solve it without considering Hibernate after all, it s purely an object-oriented problem. Notice that it s almost never correct to override equals() on a subclass and include another property in the comparison. It s a little tricky to satisfy the
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