Hibernate trap: Do not directly access fields in another entity instance

Hibernate is great, but about once a year we get bitten by using it incorrectly. Latest lesson:

Don’t directly access fields on any instance other than ‘this’. Use the appropriate getter instead. So instead of:

public void aggregateQuantity(Trade other)
{
  quantity += other.quantity;
}

use:

public void aggregateQuantity(Trade other)
{
  quantity += other.getQuantity();
}

Why? Because the other entity instance may be an uninitialized proxy and you’ll get the default value for the type (null, zero or false), not the value you are expecting.

Hibernate gives you this particular reason to not access fields on another instance, but it’s generally bad form anyway. Just being the same class as another object should not give you the right to bypass its code. The Ruby programming language gets this right:

it is never possible to access another object’s private methods directly, even if the object is of the same class as the caller.

Published 6 February 2009, tags: hibernate, java

Comments

You can email me at geeks#stephen.viles.geek.nz (change # to @).

Articles

• Producing CSV files from Java for French and German
• New York City travel tips
• Introduction to Java web applications
• Removing line noise with a user style sheet
• A pattern for scripts that update data
• Moving from Blogger to nanoc
• What's the problem we're trying to solve?
• Hibernate trap: Do not directly access fields in another entity instance
• Comparing XML using line-oriented diff tools
• Correct, in error, appropriate, or inappropriate? How are you going to know?

Copyright © Stephen Viles. You can share or adapt this material under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 New Zealand license. This site is built with nanoc and hosted by NearlyFreeSpeech.NET.