Domain-Driven Development with Context::Singleton

• name: Branislav Zahradník
• pause id: BARNEY
• github: happy-barney
• email: happy.barney@gmail.com
• pm group: Brno.pm
• working at GoodData

Why domain-driven development ?

• focus on business side of software development
• emphasize business / development cooperation
• emphasize domain expert's contribution
• emphasize minimalistic design (bounded context)

How to measure software quality

• number of bugs ?
• maintainance effort ?
• evolution effor ?

Explain DDD - Bounded context

• semantically related component
• example (taken from Domain-Driven Design Destilled)
  • product
  • backlog item
  • sprint
  • release
• bounded context looks like µservice
• reuseable (context mapping)

Explain DDD - domain language

• describes applicable scenarios using domain terms
• common for both domain experts (business) and developers
• same term can have different meaning in different BC

Explain DDD - domain event

• record of something business important
• product of domain command
• eventual consistency
• can be observed

Explain DDD - tests

• test case are described using domain language
• assert domain events
• domain expert can write or verify test case
• tests are entry point into system

DDD with Context::Singleton

• frame - flat model
• proclaim / deduce - value objects
• deduce - domain command / domain event
• trigger - observing domain events

Example - event listener

        trigger 'project::id' => sub {
            logger->mdc->set (PROJECT_ID => $_[0])
        }

Example - project backup using remote storage

        contrive 'backup::project' => (
            dep => [ qw[ project::id backup::driver ] ],
        );

        contrive 'backup::driver' => (
            class => 'Backup::Storage',
            dep => [ 'backup::storage::username', 'backup::storage::password' ],
        );

        proclaim 'Backup::Storage' => 'Backup::Storage::S3::AWS';

Example - ... timtowdi

        contrive 'net-amazon-s3-access-key' => (
            dep => [ 'backup::storage::username' ],
        );
        contrive 'net-amazon-s3-sercet-key' => (
            dep => [ 'backup::storage::password' ],
        );
        contrive 'net-amazon-s3' => (
            class => 'Net::Amazon::S3',
            dep => {
                aws_access_key => 'net-amazon-s3-access-key',
                aws_secret_key => 'net-amazon-s3-sercet-key',
            },
        )

Example - tests

• proclaim - inject state (mocks)
• deduce 'domain::command'
• assert 'domain-event' ...

        proclaim 'net-amazon-s3-access-key'    => 'Dummy';
        proclaim 'net-amazon-s3-secret-key'    => 'Dummy';
        proclaim 'net-amazon-s3-bucket'        => 'dummy-bucket';
        proclaim 'net-amazon-s3-bucket-region' => 'ca-central-1';
        proclaim 'net-amazon-s3-object'        => 'some/object';
        proclaim 'net-amazon-s3-expire-in'     => 7_200;
        proclaim 'now'                         => '2010-01-01 12:36:54';

        ok deduce ('net-amazon-s3-object-signed-uri'), ...;

Example - API versioninig

        contrive "parser/v1.0" => ( dep => [ "vnd.v1.0+json" ],  ... )
        contrive "parser/v2.0" => ( dep => [ "vnd.v2.0+json" ],  ... )

        contrive "user::login" => (
            dep => [ "parser/v1.0" ],
            as => sub { $_[0]->{login} },
        );

        contrive "user::login" => (
            dep => [ "parser/v2.0" ],
            as => sub { $_[0]->{user}{login_name} },
        );

        proclaim $request->{content_type} => 1;
        deduce "authorize::user";

Example - API versioning

        contrive "builder/v1.0" ...;
        contrive "builder/v2.0" ...;

        contrive "outout/user/v1.0" => (
            dep => [ "builder/v1.0", "user::login", "user::password" ],
            as => sub {
                $_[0]->build ({
                    login => $_[1],
                    password => $_[1],
                });
            },
        );
        contrive "outout/user/v2.0" => (
            dep => [ "builder/v2.0", "user::login", "user::password" ],
            as => sub {
                $_[0]->build ({ user => {
                    login_name => $_[1],
                    password => $_[1],
                }});
            },
        );

Books

• Domain-Driven Design Destilled by Vaughn Vernon
• Implementing Domain-Driven Design by Vaughn Vernon
• Domain-Driven Design - Tackling Complexity in the Heart of Software by Eric Evans