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[MUSIC]

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So we've chosen Hibernate as your ORM,

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and now it's time to get a grasp of the
main components we'll be interacting with.

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Check it out.

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We've already seen this basic
graphic of a Hibernate application.

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If we zoom into the Hibernate component,
we see some important pieces revealed.

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First is the session factory.

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In Hibernate, a session factory
is a fairly heavy weight object

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that contains the relationships between
the application and a database.

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There is usually just one
of these per application.

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It encapsulates all the objects related
to mapping pojos to database tables and

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columns.

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Which is contained in
the metadata sources object.

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A session represents
an interaction with the database

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in which a live connection is established.

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We'll see that before performing any
data operations we'll open a session.

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And when we're done interacting with the
data we'll immediately close the session.

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These objects are lightweight and
therefore, are created as needed.

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A transaction represents a unit of work
that must be performed on the database,

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which might in compass several queries.

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For example, a database transaction
performing a bank account transfer

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might involve deducting a hundred dollars
from one account and adding it to another.

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If adding the hundred dollars
to the second account fails,

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we want to undo the initial deduction.

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Otherwise the hundred dollars vanishes.

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In a transaction we begin the work,
perform all the queries, and

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if they succeed, we commit the
transaction, which finalizes all queries.

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If any part fails, we roll back the
transaction which will reverse each query.

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Pretty powerful stuff.

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And of course, Hibernate supports this.

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Finally, a criteria allows us to query
the database using its mapped pojo class.

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And add restrictions to
further filter those results,

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using methods that translate to
the SQL Like or > or = operators.

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At their most basic level these
restrictions translate to simple or

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compound where clauses.

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All right, now that you've seen some
of the main components of Hibernate.

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Let's dive in.

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Meet me in the next video to start coding.