Building JavaScript applicationsbased on DDD, CQRS and EventSourcing

MunichJS, 04. Sept 2014

DomainDomain Model Model

ORMORM

CRUDCRUD

Updates Manipulates

Sees Uses

Our Domain

We are a SchoolSchoolWe have StudentsStudents and CoursesCourses

Students should be able to- join a Course- leave a Course

var studentSchema = new MongooseSchema({ name: String});

var courseSchema = new MongooseSchema({ name: String});

Relationships with ORM

Students should be able to join Courses

var courseSchema = new MongooseSchema({ name: String, students: [ studentSchema ]});

app = express()

// C(reate)app.post('/course/create', course.create);

// R(ead)app.get('/course', course.read);app.get('/course/:id', course.read);

// U(pdate)app.post('/course/update/:id', course.update);

// D(elete)app.get('/course/delete/:id', course.delete);

Where did theWhere did theBusiness-Logic go?Business-Logic go?

Business -

Reporting

Which Students first joined a Course but left it again?

var courseSchema = new MongooseSchema({ name: String, students: [ studentSchema ], studentsLeftIds: Array});

// U(pdate) Routecourse.update = function(courseId, updatedCourse) { currentCourse = course.findById(courseId);

// U(pdate) Routecourse.update = function(courseId, updatedCourse) { currentCourse = course.findById(courseId);

// add students to "studentsLeft" that left the course currentCourse.studentsLeftIds = calculateStudentsLeftTheCourse(currentCourse,updatedCourse);

// save currentCourse.save()};

// U(pdate) Routecourse.update = function(courseId, updatedCourse) { currentCourse = course.findById(courseId);

// remove students from "studentsLeft" that enrolled again currentCourse.studentsLeftIds = calculateStudentsJoinedTheCourseAgain(currentCourse, upatedCourse);

// add students to "studentsLeft" that left the course currentCourse.studentsLeftIds = calculateStudentsLeftTheCourse(currentCourse, updatedCourse);

// save currentCourse.save()};

Another approachAnother approach

BoundedContext

Encapsulates your DomainModel(s)

var school = eventric.context('school');

Ubiquitous Language

Behaviors in your Domain

EventStormingEventStorming

DomainEventsDomainEvents

school.defineDomainEvents({ StudentJoinedCourse: function(params) { this.courseId = params.courseId; }, StudentLeftCourse: function(params) { this.courseId = params.courseId; }});

Aggregate

school.addAggregate('Student', function() { this.joinInCourse = function(courseId) { this.$emitDomainEvent('StudentJoinedCourse', { courseId: params.courseId }); }

school.addAggregate('Student', function() { this.joinInCourse = function(courseId) { this.$emitDomainEvent('StudentJoinedCourse', { courseId: params.courseId }); } this.leaveCourse = function(courseId) { this.$emitDomainEvent('StudentLeftCourse', { courseId: params.courseId }); }});

CommandHandler

school.addCommandHandlers({

StudentJoinCourse: function(params, done) { studentRepository = this.$repository('Student'); studentRepository.findById(params.studentId) .then(function(student) {

student.joinCourse(params.courseId);student.joinCourse(params.courseId);

studentRepository.save(params.studentId); }) .then(function() { done(); }) }

StudentLeaveCourse: function(params, done) { studentRepository = this.$repository('Student'); studentRepository.findById(params.studentId) .then(function(student) {

student.leaveCourse(params.courseId);student.leaveCourse(params.courseId);

studentRepository.save(params.studentId); }) .then(function() { done(); }) }

});

Reporting using Projections

school.addProjection(function() { this.studentsLeft = {}

this.handleStudentLeftCourse = function(domainEvent) { // make sure the object has the correct format this.studentsLeft[domainEvent.aggregate.id] .course[domainEvent.payload.courseId] = true; } });

school.addProjection(function() { this.studentsLeft = {}

this.handleStudentJoinedCourse = function(domainEvent) { // make sure the object has the correct format delete this.studentsLeft[domainEvent.aggregate.id] .course[domainEvent.payload.courseId] }

this.handleStudentLeftCourse = function(domainEvent) { // make sure the object has the correct format this.studentsLeft[domainEvent.aggregate.id] .course[domainEvent.payload.courseId] = true; } });

CQRS + EventSourcingCQRS + EventSourcing

to the Livecoding..to the Livecoding..

Johannes Becker@dieserjohannes

eventricjs.orgeventricjs.org

github.com/efacilitation/eventricgithub.com/efacilitation/eventricgithub.com/efacilitation/eventric-todoMVCgithub.com/efacilitation/eventric-todoMVC