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Moving on through the CRUD operations, you have yet to cover updating and deleting. In this lesson, you again use the Hibernate `Session` to perform these operations.
Note:
The .update() and .delete() methods in Hibernate are deprecated. They still work as expected, though you may see warnings in your IDE. It is now recommended to use .merge() for updating detached entities and .remove() for deleting entities.
If you previously utilized .persist() in place of the deprecated .save(), note that .persist() does not return the entity's ID. To retrieve the ID after persisting, simply access it using the getter (e.g., entity.getId()) after the transaction is committed, as the entity becomes managed and its ID is automatically generated.
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In the context of the basic CRUD
operations in our application,
0:00
we're only half-way there.
0:04
We've discussed creating with
a hibernate session save and
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reading with a hibernate criteria.
0:10
Let's now turn to updating and deleting so
that you have a more solid foundation for
0:12
further research and
experimentation with Hibernate.
0:17
In both the update and delete scenarios
we'll need a persistent object.
0:21
What this means is that we'll have to
have already fetched the object from
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the data base so in each of these cases
we'll first find a contact by ID.
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Let me show you how
that's done in hibernate.
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To keep our application class
tidy I'll make another method for
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getting a contact with a certain ID and
I'll include comments for
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what we're gonna do in this method.
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We'll do this right below the main method.
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We'll call it private static,
it's gonna return a contact object and
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I'll say find contact by
ID using a given int ID.
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So the first thing we'll do is open
a session, this should look familiar.
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We'll retrieve the persistent object.
1:01
Or null if it's not found.
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We'll close the session.
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And finally will return
the contact object.
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Most of this we've already done before so
I'll fill in those pieces now.
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To open the session, as you recall,
we'll declare a session and
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we'll use the sessionFactory
to open a session.
1:25
This is the line that we'll
come back to in just a moment.
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To close the session that's
a simple call to session.close.
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And finally returning that
object return contact.
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Speaking of that contact object, hibernate
provides a simple way to retrieve
1:41
a persistent object using its identifier
and that is the session's get method.
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Here's how it looks.
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So into this contact variable
we will assign session.get.
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We'll specify the name of the entity
class and we will give it
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the integer identifier associated with
the contact object that we're looking for.
2:01
And that's all we need for
the findContactById method.
2:06
Now let's write a method that
will take this contact object and
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persist any changes to the database.
2:13
Let's create the method stub and
comments for what we need to accomplish.
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I'll do that below the current method,
private static void,
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we'll call it update and we wanna
update the specified contact object.
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So again, we will open a session
here we'll begin a transaction,
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since there are changes to
be written to the database,
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we'll use the session
to update the contact.
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We'll commit the transaction and
finally we'll close the session.
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Now, all of this will likely
look fairly intuitive and
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in line with the code that
we've used to save an entity.
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In fact, the only difference is gonna be
that instead of calling the save method,
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we'll be calling sessions
update method which you
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probably could've guessed with
your IDE code suggestions.
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So let's get this thing done.
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First we will open a session.
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Session = sessionFactory.opensession.
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We'll begin the transaction by
using session.beginTransaction.
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Here's the one line that's
different from saving a new entity,
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we'll say session.update the contact.
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Then we will commit the transaction.
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Session.getTransaction, that gets
the open transaction that commit and
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finally we will close the session.
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Session.close.
3:40
Now with that done let's pull it
all together in the main method.
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So let me scroll back up
here to the main method.
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What I'd like to do is update
the contact that we saved
3:49
at the beginning of this method,
that is this contact object here.
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To do this we'll need to have its ID.
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But because this was generated by
the database we don't currently have
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access to this integer
ID in our source code.
4:04
But hibernate has a solution for that.
4:08
Whenever an entity is saved
with a sessions save method,
4:11
that save method returns
the assigned identifier,
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whether its generated by application code
or by the database, as is the case for us.
4:17
Let's scroll down to the save method and
update it to return the int id.
4:22
To do that right here we will say,
int id = session.save.
4:29
Now the save method returns
a serializable object so
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we'll need to cast that
return value to an int.
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Wonderful, next we'll return
the integer ID and add the return type.
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So at the bottom here let's return the I,
and
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instead of making this a void
method let's switch that to an int.
4:52
So we now have access to the generated
ID up in our main method.
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So I will scroll back up and
alter my code there.
4:59
So before the save I'll add
an int ID = save contact.
5:03
Let's create a log of outputs so
that we can observe the progress of
5:09
all of our steps and
verify that our update indeed works.
5:12
So this first display of our contacts is
gonna be displaying a list of contacts
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before the update.
5:20
And the next thing that we're going
to do is get the persistent contact.
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We'll update the contact.
5:30
We'll persist the changes and
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then we'll display a list of
contacts after the update.
5:39
Now let's back fill
a couple lines of code for
5:45
retrieving the contact, altering it,
then persisting those changes.
5:48
So for getting the persisted
contact we will say contact,
5:52
I'll call it C in this case, equals
findContactById, and here's the integer
5:57
Id that will have been generated when
we persisted this initial contact.
6:03
So we'll hit the database again and
grab the result as a contact object.
6:08
Then we can alter the contact
just as we would any
6:14
other Java object by using a setter.
6:17
I'll alter the first name.
6:19
So under Update the contact,
I'll say c.setFirstname and
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I'll set the first name to Beatrix.
6:25
And to persist those changes we'll
call the update method that we wrote
6:30
just a bit ago, update(c).
6:33
Now let's give ourselves
a couple lines of output so
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that we can monitor our
progress along the way.
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So right here I'll do a System.out.print
f and I will say that this,
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give myself a couple new lines,
this is before the update.
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Want those to stand out so I'll surround
that update by a couple new line
6:57
characters, now let's give ourselves
a couple lines of out put before and
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after the update so
we can monitor those changes as well.
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I'll copy that before and after this
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persist so this will be updating.
7:14
And then we'll display a message
that says update complete.
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And finally, let's display our
list of contacts after the update.
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I'm going to copy these two lines of code,
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since we'll be doing
essentially the same thing.
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We'll paste it down here and
I will change this to after
7:38
and we want to do the same thing for this
second line of code which will again fetch
7:43
all contacts, create a stream out of
it and on each one of those contact
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objects we will pass that contact object
to the system.out.println method.
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And that's all there is to it.
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Let's run our application to
verify that everything is working.
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Right click and choose run.
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And if you look closely you will see that
our first run through the output here
8:07
has our last contact, that is the one with
the ID of four as a first name of Chris.
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And then we have our update in
which this hibernate query is run,
8:20
that is sent to the database.
8:25
Upon completion,
we have our update complete,
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and here's our list after the update.
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Let's see if it worked.
8:31
Down at the bottom we have our
contact with the ID of four,
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whose last name has now been
successfully persisted to the database.
8:35
As Beatrix, first name rather.
8:40
So as a recap of what we just did,
we retrieved a persisted object that we
8:44
wanted by knowing it's ID and
using the session's get method.
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Then we altered the POJO
using a basic setter.
8:52
Finally we called the session's update
method to persist those changes.
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And just like that our changes
were persisted to the database.
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Pretty cool stuff!
9:03
You might be wondering at this point why
I haven't finished what I promised at
9:05
the beginning of this video.
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How do you delete a persisted object?
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I haven't forgotten though.
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What I'd rather do is have you take a look
at what you've learned from this course
9:16
and extend it to this one
additional operation.
9:20
The delete operation.
9:23
You can try some things using your
IDE's code suggestion tool or
9:25
you can hit up the online hibernate docs
that I've linked to in the teachers notes.
9:29
Either way, be sure to give yourself
plenty of output to verify successful
9:34
functionality.
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Though you'll get the most out
of accomplishing this yourself,
9:40
I've made my solution available on GitHub.
9:43
If you want to see it,
Go to the online repo or
9:46
check out the revision named final.
9:49
Now have at it.
9:51
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