Fri, 10 October 2014
In our last Hibernate lesson, you learned how to fix duplicate data from hibernate queries.
In this lesson we’re going to focus on some of theaggregate functions that can be used with Hibernate, and of course that means diving into the
What’s important to note is that Hibernate doesn’t ever refer to it as
So, armed with this knowledge, let’s jump into the lesson!
Grouping Data with Hibernate
In our examples, I’m going to show you how to create a query with hibernate that will group your data in some manner.
When we build our query, we will be focusing on using Hibernate’s
First, let’s start off with an example that we will build on.
Mon, 15 September 2014
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
Consider this scenario… A
So what happens when you run a query that joins to the
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:
Fri, 5 September 2014
Now it’s time to dive into the nitty gritty of Hibernate’s mysterious inner workings.
I’m by no means an expert in Hibernate, but I do use it almost every day for my own projects, so I do know a thing or two about how it works.
One topic that had me scratching my head for ages was the Hibernate life cycle. What I mean by the life cycle is the way Hibernate interacts with Java objects at certain points in the existence of said Java objects.
Let’s start from the beginning…
What the heck is a Hibernate Life Cycle?
You see, Hibernate is picky about your Java objects. Hibernate prefers your objects to be in a certain “state”, known as the persistent state… this persistent state is one of four different states that exist inside of the hibernate persistence life cycle.
Once you have a firm grasp of the different states that an object can be in (as it pertains to Hibernate) you’ll be well on your way to mastering the Hibernate framework.
So let’s get this Hibernate persistence life cycle lesson started shall we?
Continue reading via: http://howtoprogramwithjava.com/session58
Wed, 27 August 2014
What the heck is a Fetch Type?
Great question! Hibernate is a very handy framework for removing your need to fully understand SQL, but it will force you to understand things such as joins.
Joining two tables in SQL is the foundation of a relational database, as joins allow you to actually define relationships between tables (objects).
Having said that, relationships are important to understand when talking about fetch types in Hibernate. This is the case because whenever you define a relationship in Hibernate, you’ll also need to define the fetch type. The fetch type essentially decides whether or not to load all of the relationships of a particular object/table as soon as the object/table is initially fetched.
For more information please see the show notes via http://howtoprogramwithjava.com/session57
Thu, 21 August 2014
Hibernate @ManyToMany Unidirectional
The Many-to-Many relationship can be best described by example.
The example we’re going to use is that of the relationship between an
Other examples of the many to many relationship are Students to Courses and Employees to Projects.
Let’s take a look at how the unidirectional many-to-many relationship is created using Hibernate... for more info please visit http://howtoprogramwithjava.com/session56
Thu, 7 August 2014
One-to-One Unidirectional Relationship
We will start things off with the unidirectional One-to-One relationship and how it’s set up in Hibernate.
First thing is first, you need to understand how a One-to-One relationship is actually set up in a database. Once you understand that the child table declares the parent’s primary key as the child’s primary key, then we can get moving with the Hibernate stuff!
For this example, we are going to use the One-to-One relationship between an
For more information, please read the show notes via http://howtoprogramwithjava.com/session55
Mon, 28 July 2014
Since we’ve already learned about the unidirectional @ManyToOne relationship, we can now move on to talking about what a bidirectional relationship is like, when using Hibernate. The term “bidirectional” literally means “functioning in two directions”, which is the concept that we will apply in our relationships between two Java objects. When we have a bidirectional relationship between objects, it means that we are able to access Object A from Object B, and Object B from Object A. We can apply this logic to our real world coding example that we saw in the last post. The example we will use is the relationship between an Employer and an Employee. Previously, we only defined a unidirectional relationship, so we could only access the Employer from the Employee object and not vice-versa. Now let’s take a look at how to transform our existing unidirectional relationship into a bidirectional one.
Wed, 23 July 2014
But now I want to talk about how to create those same relationships inside of Hibernate.
Specifically, I want to focus on the One-to-Many relationship in Hibernate and how we go about mapping it out in our Java objects.
But before we do, a word on unidirectional and bidirectional relationships.
Unidirectional vs Bidirectional
In Hibernate, it’s possible to map all three relationships that are available in a standard database, these include:
But what Hibernate also includes is the ability to make EACH of those relationships either unidirectional or bidirectional.
This means that we can have a unidirectional One-to-One and a bidirectional One-to-One mapping, as well as a unidirectional One-to-Many and a bidirectional One-to-Many, as well as a unidirectional Many-to-Many and a bidirectional Many-to-Many relationship.
That’s a lot of relationships!
So what exactly are unidirectional and bidirectional relationships?
Learn more on the show notes page via http://howtoprogramwithjava.com/session53
Tue, 15 July 2014
Data Access Objects – What are they?
Data Access Objects (or DAOs for short) are used as a direct line of connection and communication with our database. DAOs are used when the actual CRUD (CRUD = Create, Read, Update, Delete) operations are needed and invoked in our Java code. These data access objects also represent the “data layer” of our application.
These objects are still just plain old Java objects that incorporate the use of some Hibernate annotations to give them the functionality we need from them. Again, that functionality being the communication with the database.
Also, believe it or not, the concept of creating a file specifically for accessing the database is a design pattern. It’s called the Data Access Object Pattern and you can read more about it from this nice short Wiki article.
What Hibernate Annotations Should We Use?
Okay, so now that you’re somewhat familiar with DAOs, it’s time to learn how to integrate these plain old Java objects with our Hibernate framework (so they actually do the work we need them to do).
There are two main annotations that you need to be familiar with:
To learn more, visit our show notes page via http://howtoprogramwithjava.com/session52
Tue, 8 July 2014
What You’ll Learn
The focus of this podcast / blog post is to teach you how to create the connection between your Java objects and the SQL Database tables. Remember, the whole point of the Hibernate framework is for you to be able to write Java code that allows you to communicate with your database.
When I say that the goal is to communicate with your database, what I mean is:
What we’re going to be tackling in this post will the step #1, how to get Hibernate to create our tables for us.