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Before completing our configuration there
is some other coding that we have to do

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and some other concepts
that we need to understand.

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So we'll be returning to
that XML file in just a bit.

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As you've seen, the power of Hibernate and
really any ORM lies in its ability to let

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you, the developer, focus on Java code,
while Hibernate takes care of the details

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of fetching, adding, editing and
deleting POJOs from the database.

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These POJOs though in our
case the contact class

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need to be configured in a certain way for
Hibernate to understand

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how to map its fields to database
columns in a contact table.

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This is where it's
helpful to know about yet

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another acronym JPA J P A stands for
Java Persistence.

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A.P.I. and

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is a set of interfaces that our ORM's can
implement to provide data persistence.

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Remember, that's just long lasting data
storage being a set of interfaces or

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ORM's including hibernate can choose to

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implement these in
whatever ways they desire.

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As a developer though using J P A in
our code means that we can swap out

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the implementation, that's the RM,
while minimizing the impact on our code.

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Some application servers provide
an implementation of JPA at runtime.

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Such as J.

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Boss.

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But there is no such thing
as a JPA only solution.

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Why?

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Because JPA is not an implementation but
rather a contract.

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It's like an expectation you can have
when you use an implementation such

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as Hibernate.

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Like the expectation that the plug
of a new pair of headphones will fit

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into your iPhone or Android phone or
Windows phone or even your computer.

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You expect that they'll fit
regardless of the device programming

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that controls the audio signal itself.

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But the presence of a headphone jack
isn't enough to make Mumford and

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Sons pump through to your ears.

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For that there must be actual device
programming that reads an audio file and

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creates a sound signal that is
sent to the headphone interface.

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Okay, you get it.

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J P eight isn't an implementation, but it
includes the annotations that we'll use on

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our contact pojo to indicate how we want
to map its fields to database columns.

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Let's see what that looks like.

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Since we don't yet have a package for our
application code let's create that now.

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I'll right click on JAVA and choose
new package and for the name I'll use

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com.teamtreehouse.contactmgr and
hit enter.

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And no we won't play as much code in there
just yet, let's create our main class and

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call it application.

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So on that package that I just created,
I'll right click and

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choose new Java class and
name an application and

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in here is where our public
static void main method will go.

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So, I'll get that in there now for
later use.

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Let's create a sub package of the one
we just created where we could stick

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any model or entity class we might need.

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So I'll right click on this package and
choose new package and name it model and

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into it we'll put the only model class
we'll be creating in this course,

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the contact class.

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So I'll create that now,
New Java class and call it contact.

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I'll quickly code this class but

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feel free to copy paste from
the one we used in work spaces.

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So we'll get our id in there as
well as our firstName lastName.

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Email and

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phone.

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Now I'll use intelligent code generation
to get some getters and setters.

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And this time, we will need the setters.

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So I'll choose getters and setters,
highlight all of them and hit enter.

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And boom there are our getters and
setters.

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And because J.P.A. will call our default
constructor when instantiating contact

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objects we need to make
sure one is present.

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With no other constructors in this class
and no constructors explicitly defined in

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a superclass the compiler will
provide a default constructor for us.

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But for purposes of clarity,

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will explicitly define a default
constructor in case we need to go back and

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add a non default constructor and as
a heads up we will end up doing just that.

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So let's create that now and
leave it empty.

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This will be our default constructor for
J.P. A public.

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Contact.

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And I'll even do it in one line.

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Beautiful.

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Let's also generate a two string
method using all of our fields.

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So again I'll use
IntelliJ's code generation.

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And arrow down to toString0 method and

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include all fields in
the toString0 it's generating.

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Now it's time to add those J.P.A.
annotations.

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The one will start with
is the entity annotation.

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This is the one that will mark this class
as want to persist to the database.

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By default, entities are given
their own table in the database.

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So we will decorate our class.

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With the Javax.persistence.entity
annoation.

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When hibernate detects this annotation,

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it will map a contact object to a single
row in the contact table of the database.

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There is an optional name element for
the entity annotation and you can specify

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a value here if a value is provided that's
what will be used as the map's TableName.

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By default though,
the class name is used and

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will stick with that
default in this course.

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As for the fields,
we'll skip over the id field and

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mark all the others with
a @Column annotation.

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And again this comes from
the javax.persistence library.

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That is the JPA library.

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These annotations are self describing
in that each of these fields will

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be mapped to a column
of the contact table.

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Again, the name element can be used to
specify the column name, but by default,

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the field name will be used and again will
stick with the default in this course.

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Now back up to the ID field.

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We'll use a special annotation here to
indicate that this field is to serve

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as this entities primary key.

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Now quite intuitively,
it's the ID annotation.

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And if you want this value to be
automatically generated by Hibernate,

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you can use the generated
value annotation,

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specifying the strategy to be used for
generating new IDs.

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In our case,
we'll use GenerationType.IDENTITY.

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Now it turns out that
since we included an ID

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annotation on a field that every other
field unless marked as transients.

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Either with a JAVA modifier or
with the transience annotation.

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Will be automatically
mapped to a database column

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even without these column annotations.

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I'll leave them there though.

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Just for purposes of demonstration.

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One final task before we take a break.

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I mentioned earlier that we'd be
returning to that XML configuration file.

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Let's do that now.

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There are two more elements
that we need to add.

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The first calls upon a Hibernate
tool to generate our database schema

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based on our annotated entities.

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Let me stick a comment in there.

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That references what this
property is going to be doing.

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So we want to create the database schema.

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On application start up.

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And to accomplish this we
are going to use another property.

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The name of this property is
going to be hbm2ddl.auto.

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And the value we're going
to use here is create.

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Now hbm2ddl stands for hibernate
mapping to data definition language.

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This particular setting tells hibernate to

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create the schema upon
starting the application.

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It will do this by reading the hibernate
configuration file, looking for

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mapped entity classes, and then examining
those classes, JPA annotations,

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to create database tables and columns.

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You might wonder then,
how does this configuration file

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inform hibernate that we
have a mapped entity class?

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The answer is that we add a mapping
element indicating the fully qualified

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name of the entity class.

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I say fully qualified because that name
must include the package name as well.

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Let me get a comment in here for
this mapping element.

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This is going to name
the annotated entity classes.

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In our application we'll
have only one class.

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This XML element is called mapping and
it has a single attribute named class and

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it has no inner text so I'm going to
create it as a self closing element.

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As I said before, the name of this class
has to be fully qualified which means it

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includes the package name,
in our case com.teamtreehouse.contactmgrif

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the.model.Contact, and there is the fully

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qualified name of our entity class
that includes our JPA annotations.

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Hey great work on getting things
ready to go for hibernate.

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Why don't we stop for a quick check for
understanding before moving on to create

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the hibernate objects that will connect
our application to a maps database.