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Let's begin setting up validations and
constraints for

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the user model to prevent invalid data
from being entered into the database.

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As I demonstrated in the previous video,

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null by default is an allowed value for
any attribute or column of a model.

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Sending an empty post request or
even setting a property explicitly to

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null allows User.create() to be
called here in the post users route and

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successfully create a new user entry.

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We don't want that.

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First, we'll make sure that a null
value is not allowed for name,

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email, birthday, and password using
the Sequelize allow null check.

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If any of these attributes are null,

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the new user entry will not be stored and
a validation error will be thrown.

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Inside the name attributes object,

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I'll add the allowNull option and
set it to false.

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I'll do the same for email,
then birthday, and finally password.

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Over in Postman,
I'll try to send a post request to the API

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users routes with missing attributes or

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fields in the body,
an empty object for example.

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Notice how I receive a 400 bad request
HTTP status code back from the server.

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And the response body displays
the validation error messages thrown by

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sequelize, preventing unreliable data
from being stored in the database.

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So here in the post users route
handler function in routes.js,

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the error is thrown in the try block,
user.create does not get called.

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So the statements in the catch
block execute instead.

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I've also added a console.log
statement here in the catch block,

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where I'm logging error.name.

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So we're able to see
the error being thrown.

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Notice in the terminal that the error
log is a sequelize validation error.

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As you've noticed from working with
sequelize in previous lessons,

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the format of its errors contains more
information than what's typically

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necessary to return to the client.

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So for this workshop,

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I have also transformed errors to
a more straightforward format by first

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checking if the error caught by catch
is a sequelize validation error or

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a sequelize unique constraint error,
which I'll talk more about later.

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Then I'm iterating over the errors
array that's in the sequelize error

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passed to the catch block to
access only the error messages and

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sending the error messages
back to the client,

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as you can see here in the response body.

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Else any other error will be
thrown here and caught up here and

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the asyncHandler function
that wraps each route.

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More about this handler
in the teachers notes.