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Let's say we wanted to create the default
animal to be saved if we don't supply

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any data to the model.

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Mongooses schema lets us as defined
default values very easily.

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00:00:13,350 --> 00:00:17,688
Let's change the schema to give
us a goldfish animal as default.

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00:00:24,004 --> 00:00:26,801
Instead of just specifying a type,

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we can give each property a type and
a default value.

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Goldfish are small,

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golden and really light in

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comparison to elephants,

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and named Angela?

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Anyway, now we can create
a generic animal with our model by

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passing an empty object into it.

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00:01:33,124 --> 00:01:36,807
And when I say a generic animal,
I mean a goldfish.

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If we were just to call
save on the animal,

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under elephant.save,
we could run into problems.

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The save method runs asynchronously.

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It's impossible to know which
save will finish first.

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If the elephant saves finish first,
it will close the database connection.

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The generic animal won't be saved.

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Instead, we'll place the goldfish.save
inside the other's callback and

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put the db.close inside
the goldfish's callback

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to ensure the correct sequence of events.

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Remember we already have
an elephant in the database.

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Running this file again
will create another one.

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00:03:06,930 --> 00:03:09,870
Let's empty the animals
collection before we save it.

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00:03:11,020 --> 00:03:13,770
The model can do this for us.

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Let's ask the model to empty our animals
collection before we save anything.

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00:03:25,646 --> 00:03:29,928
We can do this by calling the remove
method on the animal model and

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passing in an empty object.

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We could specify which documents we
want to remove by passing in a query

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object here.

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But if we leave all of the properties
blank, it will remove all documents.

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A query object would match
properties from itself

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against properties of
documents in the database.

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Any matching documents would be removed.

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We want all the save actions to
take place after the removal, so

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we'll route this code in removes callback.

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Now when we run this script We'll start
with an empty collection every time.

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Let's run this file in the terminal and
then check the database.

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There's the default animal,
a goldfish, and an elephant.

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Let's save one more animal, a whale,

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to show that these defaults
can be overwritten.

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Let's create a variable called whale and
call the animal constructor.

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The type is whale.

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00:06:06,858 --> 00:06:14,039
The size is big.

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The mass is 195,500 kilograms.

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Wow.

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And its name is Fig.

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00:06:36,200 --> 00:06:40,121
Notice we're not supplying the color here.

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The whale should pick up
the color from the defaults.

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Let's save it after we save
our other two animals.

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Before we run this, let's also see how
we can read animals out of the database.

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Let's ask the model for
all big animals, and

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then write out their names to the console.

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The models find method takes in
an object as its first parameter.

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This object should contain keys and
values you want to match to your results.

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The second parameter is a callback
function that passes in an error object

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and the results from your query.

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Let's print out each one of
the results in the console now.

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console.log(animal.name +) "

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the " animal.color,

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+" " + animal type.

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Just a note here.

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You see this pattern we're building
up with all these callbacks?

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This is a common pattern in Node, which
you may have seen or experienced before.

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Manage an asynchronous calls by
nesting them inside a callback

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after another callback.

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This is known as the pyramid of doom.

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But we're just playing around
with Mongoose to just get a feel

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of how it works.

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Our code in the rest API we're going to
build won't suffer from this as much.

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Special objects called promises can
help us manage asynchronous code and

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make it easier for
us to read and work with.

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00:09:47,880 --> 00:09:51,620
Treehouse content that covers
promises is in the teachers notes.

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00:09:51,620 --> 00:09:54,533
However, we're not using
promises in this course.

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Also, we'll clean up a lot of
this code in the next video.

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In the terminal, run this file again.

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The data was successfully submitted and

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that the models were found that
are big animals that we asked for.

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There we have the golden whale, Fig.

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Fig is golden because the default
values were specified in the schema.

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So far, we've performed three of the four
basic database operations with Mongoose,

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namely reading, writing, and deleting.

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00:10:31,480 --> 00:10:33,660
Updating is a similar process.

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00:10:33,660 --> 00:10:35,740
We'll cover that later.

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Now let's look at some more advanced
things you can do with Mongoose.