Domain Driven Design for Angular

Domain Driven Design for Angular

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  1 Domain Driven Design forAngular
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  Discussion Agenda • Whatis DDD? • Business Application Practices • Onion Architecture • Dependency Inversion Principle • Building Blocks –Entities –Value Objects –Aggregates –Factories –Services –Repositores –Domain Events 2
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  What is DomainDriven Design? 3 A domain is a “sphere of knowledge or activity around which application logic revolves”. In DDD, we seek to isolate our business realm of operation [our domain] and design an application tailored to it. To do this, we must define the domain layer or domain logic, AKA ‘business logic’. DDD lets us build a custom app suited to our domain layer.
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  Business Practices forFocusing on the Core Domain 4 •Context: The setting in which a word or statement appears that determines its meaning. Statements about a model can only be understood in a context. •Model: A system of abstractions that describes selected aspects of a domain and can be used to solve problems related to that domain. •Ubiquitous Language: A language structured around the domain model and used by all team members to connect all the activities of the team with the software. •Bounded Context: A description of a boundary (typically a subsystem, or the work of a specific team) within which a particular model is defined and applicable.
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  Onion Model forDDD 5
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  Onion Model forDDD 6 • The Core contains the building blocks not specific to any domain or technology. The core contains domain objects such as entities, value objects, custom types and aggregates. • The Domain contains all business logic. Classes and methods should be named using the ubiquitous language for the domain. • The API contains methods which can be used to access the core and domain objects (repositories, etc) • The Infrastructure is a bridge between domain objects and any infrastructure (typically databases). This layer contains adapters which connect the domain to any databases or services.
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  Dependency Inversion Principle 7 DependencyInversion forms the I in SOLID design: “Interface Segregation Principle” Sockets isolate what is behind the wall, on the other end of the plug, etc. Angular Dependency Injection lets us “plug in” modules to our code, like the USB plugs in the picture.
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  Building Blocks ofDDD 8 Domain Driven Design defines high level concepts which can be used to create and work with Domain Models
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  Building Blocks ofDDD - Entity 9 Entity An object that is identified by its consistent thread of continuity, as opposed to traditional objects, which are defined by their attributes. Entities are defined in interfaces. Entities are data models. Reducers are Entity Adapters.
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  Building Blocks ofDDD – Value Object 10 Value Object An immutable (unchangeable) object that has attributes, but no distinct identity. Value Objects are defined as constants or in config tags. Value Objects can be data models. Value Objects are part of the core business logic.
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  Building Blocks ofDDD – Domain Event 11 Domain Event An object that is used to record a discrete event related to model activity within the system. While all events within the system could be tracked, a domain event is only created for event types which the domain experts care about. Observables in Angular [event system, HTTP service] are examples of Domain Events.
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  Building Blocks ofDDD – Aggregate 12 Aggregate A cluster of entities and value objects with defined boundaries around the group. Rather than allowing every single entity or value object to perform all actions on its own, the collective aggregate of items is assigned a singular aggregate root item. Now, external objects no longer have direct access to every individual entity or value object within the aggregate, but instead only have access to the single aggregate root item, and use that to pass along instructions to the group as a whole. Grouped UI data objects are Aggregates
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  Building Blocks ofDDD – Service 13 Service Essentially, a service is an operation or form of business logic that doesn’t naturally fit within the realm of objects. In other words, if some functionality must exist, but it cannot be related to an entity or value object, it’s probably a service. Angular Services implement this building block!
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  Building Blocks ofDDD – Repository 14 Repository Not be confused with common version control repositories, the DDD meaning of a repository is a service that uses a global interface to provide access to all entities and value objects that are within a particular aggregate collection. Methods should be defined to allow for creation, modification, and deletion of objects within the aggregate. However, by using this repository service to make data queries, the goal is to remove such data query capabilities from within the business logic of object models. Angular Services are used to create Repositories
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  Building Blocks ofDDD – Factory 15 Factory As we’ve discussed through a number of design patterns articles already, DDD suggests the use of a factory, which encapsulates the logic of creating complex objects and aggregates, ensuring that the client has no knowledge of the inner-workings of object manipulation. Angular Factories are similar to Services, but create and enhance (map, convert properties, lookup, etc) objects before returning them.