WEBVTT

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Hello. I'll be introducing Voyage,
a wrapper for NoSQL databases,

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in this class.

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The goal is to let you build
a real application.

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You'll be able to store objects
like TinyBlog with Voyage,

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in a Mongo database,
and deploy on a real service.

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I also wanted to show you

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an easy way to store objects.

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Voyage is a simple solution.

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First, what is MongoDB?

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Mongo is a new document-oriented
NoSQL database.

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It features a powerful query language.

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Mongo is also one of the most popular
DBs, with CouchDB and Riak.

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We'll be using Mongo and Voyage.

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Actually, Voyage is a mapper.
It takes objects and maps them

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on MongoDB, almost automatically,
for the programmer.

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If you've done Java on Hibernate

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Voyage is the equivalent of Hibernate
for MongoDB.

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And it's made for Pharo.

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Here are Voyage's features.
It's very simple.

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It ensures object identity
when you reload them.

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It provides error-handling.

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And it also implements
a connection pool

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to speed things up.

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To start simple,
the first thing we'll do

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is create a MongoRepository.

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It uses these expressions:

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You want to access
your Mongo database,

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which is managed from outside Pharo.

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Often, when we are in prototype mode,

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we use a Mongo database
in the memory.

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It's referred to here
as Mongo Memory Repository.

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You don't need a Mongo database.
First, you prototype your application.

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When it is running right,
you switch the memory repository

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into a real repository,
and tackle your outside DB.

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That's the way to proceed.

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To illustrate Mongo,

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we have a simple model
of superheroes with superpowers,

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their armor and weapons.

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You'll be able to do the exercise
based on what I show you in the course.

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This is the support.

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I think you'll enjoy scripting Superman.

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First, let's look at how
Hero and Power operate.

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Basically, we have a Hero class,
with a name, level, and powers.

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I have an accessory for the name,
a setter for the name.

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Same for the level, here.

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And I manage the powers
as a set.

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If powers is empty,
I put in a set.

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When I can add a power,
I add one to the set.

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So it's really very basic.

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For the moment, the powers
only have a name.

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You can write the name or not.

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Now, the point is
to find a way to declare

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that my domain classes
are stored in a database.

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The root class idea gives us
an entry point for our database.

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It can be any class in the system,
and it is marked as the root

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with a class method (I emphasize class)
called isVoyageRoot.

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This is how we do it for Hero class:
isVoyageRoot returns true.

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At this point, Voyage knows
I will be able to store my heroes

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in the Mongo database.

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Let's do Spiderman.

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His name is Spiderman,
his level is epic.

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His powers are his super strength,
his ability to climb walls,

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and the spider instincts
he is purported to have.

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I save that information.

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"Save" tells Voyage
to take this superhero,

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and store it in the base.

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We do the same thing
with Wolverine and his powers,

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and save that data.

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Now, if I look at my Mongo base,

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using db.Hero.find,

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I see my hero Spiderman,

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and I should see his powers.

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This is where you have
to be careful.

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His superpowers are described
in full here.

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Same for Wolverine, etc.

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Once you've done that,
you can do lots with Pharo.

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I won't go into the details.
But I can select all the superheroes...

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That gives me Spiderman
and Wolverine.

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I can say find Spiderman...

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I can say I want to find all superheroes
who have an epic level.

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That gives me my two superheroes.

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I can also express it differently.

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Actually, the Mongo database

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understands Json,
so I can create Json on the fly,

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inject it, and do Json-based queries.

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Let's say I want to know

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which superhero is named Spiderman.

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But I've expressed it in Json form,
as dictionary, so it returns an entry.

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I can do the same thing
with "select Many."

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It depends on the easiest way
for expressing your query.

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But that's a detail for you, right now.

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You can do much more advanced queries.

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I can say "select all" the heroes

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or "many" of the superheroes
with an epic level.

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I can sort their names
in ascending order.

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I set a limit of 10,
and say I want to start at page 0.

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That will bring me sections
of the database.

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When you need that,
look in the documentation.

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We can do other operations,
like count our superheroes.

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I can count those whose possess
a certain property.

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I can remove some.
If I remove all, I empty the database.

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Be careful of that command.

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Here, I can select one,
and remove it.

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That hero will be removed from the base.

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These are all operations
that make sense.

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Now, the question that will arise
when using MongoDB

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is, what is the base root,
in Mongo lingo?

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When is a class defined as a root?

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The answer is,
if you want to query that class.

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That's the first rule.

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I define that class as a root,

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because I want to have access
to all the objects in the class.

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The other reason
is wanting to be able to share

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these objects between roots.

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Say I want to share powers,
to make it clearer.

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I want to be able to share powers
between heroes.

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In that case, I have to define
power as a root.

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Watch this.

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In our example, hero is a root.

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But power can also be a root.

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In Voyage, you can declare
any class as a root.

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Here is how to do it.

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I say Power class isVoyageRoot.

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Now, if I create the power "Fly,"

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and save it, it is in the base.

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Superstrength? The same.

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Now I'll be able to make a query

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that tells Voyage to get
the power to fly.

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I also want Voyage to get
the power of superhuman strength.

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And now I recreate Superman.

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I say, "Hey!

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I got these two powers, so there's
only one in the system, and I save it.

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But it's important for me
to reset the base

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so that it works right,

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whenever you change the basic schema.

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But now I want to show you
what I have now.

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Superman's powers
are described differently.

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The power isn't composed inside.
I have a reference to a power.

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That means if I have another superhero
who knows how to fly,

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I can share that superpower,
instead of having two instances.

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So, depending on your domain
and how you want to modelize it,

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you'll define roots differently.

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This silly example
is just to give you an idea.

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Actually, if I repeat myself,
you define a domain root

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if you want to query it
or share objects in the root.

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In Voyage, relationships are expressed

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the way "foreign keys" are
in relational databases.

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Voyage automatically handles
cyclic references of root objects.

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But be careful:
Voyage does not support cyclic references

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between embedded objects.

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You'll experiment, and see.
If you have roots, you're home safe.

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In this course, I wanted to show you
how easy it is to store objects

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in a Mongo database.

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If you want to know more, look at
Enterprise Pharo: a Web Perspective.

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It's in the MOOC resources.

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You can also refer to a little tutorial
on building the superhero base.

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You can learn it all.