Fixing Duplicate Data from Hibernate Queries
How to Program with Java Podcast15 Sep 2014

Fixing Duplicate Data from Hibernate Queries

How to Fix Duplicate Data from Hibernate Queries

This problem was the bane of my existence when I first started using Hibernate because I had no idea where the problem was coming from.

If you're executing a query and finding that you have a bunch of duplicate records and haven't a clue why, then you're in the right place.

You see the problem is typically caused by having left joins (or optional joins) in your objects. When you have a base object, like say User and it joins to another table/object in an optional One-to-Many or optional Many-to-Many format, then you may get duplicates.

Consider this scenario… A User objects joins to the LoginHistory object, which keeps track of all the times a particularUser has logged into the system. And let's say our user has logged in many times. You'll have a situation where you have many records in the LoginHistory table.

So what happens when you run a query that joins to the LoginHistory table? Well it will return as many rows as there are entries for that User in the LoginHistory table.

So because of this, Hibernate doesn't massage the data for you, it just returns exactly what it got from the database. The ball is in your court to tell Hibernate what to do with records it has retrieved.

There are two solutions to this problem:

  1. Declare your joining object as a Set
  2. Make use of Distinct Root Entity Results Transformer

Click Here to Keep Reading

Episoder(112)

EP49 - Top 3 mistakes coders make when applying to their first job

EP49 - Top 3 mistakes coders make when applying to their first job

In this episode we'll talk about 3 big mistakes that aspiring coders make when trying to land their very first job. Getting your first job as a coder will be the most difficult challenge when trying t...

31 Jul 202135min

EP48 - Top 3 reasons why you'll fail to succeed as a coder and how to overcome them

EP48 - Top 3 reasons why you'll fail to succeed as a coder and how to overcome them

In this episode we'll talk about 3 common issues I see that beginner programmers struggling with most when starting the journey of learning to code. Impostor Syndrome  The overwhelming number of choi...

29 Jul 202144min

EP47 - Key #2 of 3 to Getting a Job as a Coder

EP47 - Key #2 of 3 to Getting a Job as a Coder

Interested in starting your coding career? I'm now accepting students into an immersive programming Bootcamp where I guarantee you a job offer upon graduation. It is a 6 month, part-time, online Bootc...

22 Jul 202137min

EP46 - Are Coding Bootcamps Worth It?

EP46 - Are Coding Bootcamps Worth It?

Interested in starting your coding career? I'm now accepting students into an immersive programming Bootcamp where I guarantee you a job offer upon graduation. It is a 6 month, part-time, online Bootc...

15 Jul 202138min

EP45 - Key #1 of 3 to Getting a Job as a Coder

EP45 - Key #1 of 3 to Getting a Job as a Coder

Interested in starting your coding career? I'm now accepting students into an immersive programming Bootcamp where I guarantee you a job offer upon graduation. It is a 6 month, part-time, online Bootc...

8 Jul 202148min

EP44 - How to get a Job as a Java Programmer

EP44 - How to get a Job as a Java Programmer

Interested in starting your coding career? I'm now accepting students into an immersive programming Bootcamp where I guarantee you a job offer upon graduation. It is a 6 month, part-time, online Bootc...

7 Okt 201920min

EP43 - Resume Writing Tips

EP43 - Resume Writing Tips

Interested in starting your coding career? I'm now accepting students into an immersive programming Bootcamp where I guarantee you a job offer upon graduation. It is a 6 month, part-time, online Bootc...

1 Okt 201920min

EP42 - Java Careers and What they Pay

EP42 - Java Careers and What they Pay

Interested in starting your coding career? I'm now accepting students into an immersive programming Bootcamp where I guarantee you a job offer upon graduation. It is a 6 month, part-time, online Bootc...

23 Sep 201918min

Populært innen Business og økonomi

stopp-verden
lydartikler-fra-aftenposten
dine-penger-pengeradet
e24-podden
rss-penger-polser-og-politikk
rss-borsmorgen-okonominyhetene
pengesnakk
utbytte
livet-pa-veien-med-jan-erik-larssen
tid-er-penger-en-podcast-med-peter-warren
finansredaksjonen
pengepodden-2
morgenkaffen-med-finansavisen
rss-sunn-okonomi
stormkast-med-valebrokk-stordalen
rss-markedspuls-2
okonomiamatorene
lederpodden
liberal-halvtime
rss-politisk-preik