// Validation function to return a course's name given a numeric Id
public static string GetCourseNameById(int Id)
{
var Db = new StreamAggregatorContext();
var result = Db.Courses.FirstOrDefault(p => p.CourseId == Id);
return(result == null ? "" : result.Name);
}
// Clean table Person of all its records
static void CleanTablePerson()
{
var Db = new StreamAggregatorContext();
Db.Persons.RemoveRange(Db.Persons);
Db.SaveChanges();
}
// Clean table Course of all its records
static void CleanTableCourse()
{
var Db = new StreamAggregatorContext();
Db.Courses.RemoveRange(Db.Courses);
Db.SaveChanges();
}
// - Import the event stream from external JSON file into local data structure
// - Process the event stream in chronological order and - after successful validation
// of each event - write data to local data structures
// - Finally, output the contents of all data structures
static void Main(string[] args)
{
// Specify options for built-in JSON serializer
var options = new JsonSerializerOptions
{
PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
IgnoreNullValues = true,
WriteIndented = true
};
// Specify options for json.net (Newtonsoft) serializer
var settings = new JsonSerializerSettings
{
NullValueHandling = NullValueHandling.Ignore,
MissingMemberHandling = MissingMemberHandling.Ignore
};
// Import the event stream from external JSON file into local string
var jsonString = File.ReadAllText("events.json");
// This statement failed with given JSON file structure, so json.net (in next statement) was utilized instead
// var jsonModel = JsonSerializer.Deserialize<EventStream>(jsonString, options);
// Port imported JSON string data into List object
var jsonModel = JsonConvert.DeserializeObject <List <EventStream> >(jsonString, settings);
// Display the events to be processed (only used initially for testing)
// DisplayEventStream(jsonModel);
// Clear all tables of their contents
CleanAllTables();
// Process all events in chronological order by storing their data in data structures
ConsumeEvents(jsonModel);
Console.WriteLine();
// Output the data stored
Console.WriteLine("Course:");
Console.WriteLine("-------");
var DbC = new StreamAggregatorContext();
Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(DbC.Courses, options));
Console.WriteLine();
Console.WriteLine("Person:");
Console.WriteLine("-------");
var DbP = new StreamAggregatorContext();
Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(DbP.Persons, options));
Console.WriteLine();
Console.WriteLine("Course Enrollment:");
Console.WriteLine("------------------");
var DbC2 = new StreamAggregatorContext();
Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(DbC2.Courses.Include(c => c.CoursesEnrolled).ThenInclude(ce => ce.Person).ToList(), options));
// Console.WriteLine(modelJson);
}
// Validation function to return a boolean based on whether an enrollment by the given CourseId and PersonId exists
public static bool EnrollmentExistsByIds(int CourseId, int PersonId)
{
var Db = new StreamAggregatorContext();
return(Db.CoursesEnrolled.Any(ce => ce.CourseId == CourseId && ce.PersonId == PersonId));
}
// Process/consume an event given in EvIt according to its event name, stream id and other arguments
static void ConsumeEvent(EventStream EvIt)
{
var Db = new StreamAggregatorContext();
switch (EvIt.Event.ToLower())
{
case "person_new":
// Add new person to (local) data structure
// Check first whether a person with same Id already exists
var existingPerson = Db.Persons.FirstOrDefault(p => p.PersonId == EvIt.StreamId);
if (existingPerson == null)
{
// Person does not exist, so make sure name has been provided,
// and, if so, add new person to (local) data structure
if (EvIt.data.Name != "")
{
// Instantiate a new Person object, populate its properties..
var newPerson = new Person();
newPerson.PersonId = EvIt.StreamId;
newPerson.Name = EvIt.data.Name;
// ..and add it to the data structure Persons
Db.Persons.Add(newPerson);
Db.SaveChanges();
// Log that "person_new" event was successfully processed
AddToLog(EvIt.EventId, EvIt.StreamId, $"Successfully processed event '{EvIt.Event}' to add person '{newPerson.Name}' with Id={newPerson.PersonId}.");
}
else
{
// Issue error that new person name has not been provided
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to missing person name.");
}
}
else
{
// Issue error that person already exists and cannot be replaced/overwritten
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to person {EvIt.data.Name} already existing.");
}
break;
case "course_new":
// Add new course to (local) data structure
// Check first, if course already exists
var existingCourse = Db.Courses.FirstOrDefault(c => c.CourseId == EvIt.StreamId);
if (existingCourse == null)
{
// Course does not exist, so make sure course name has been provided, and if so,
// add it to (local) data structure
if (EvIt.data.Name != "")
{
// Instantiate a new Course object, populate its properties..
var newCourse = new Course();
newCourse.CourseId = EvIt.StreamId;
newCourse.Name = EvIt.data.Name;
// ..and add it to the data structure Courses
Db.Courses.Add(newCourse);
Db.SaveChanges();
// Log that "course_new" event was successfully processed
AddToLog(EvIt.EventId, EvIt.StreamId, $"Successfully processed event '{EvIt.Event}' to create course '{EvIt.data.Name}'.");
}
else
{
// Issue error that course name has not been provided
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to missing course name.");
}
}
else
{
// Issue error that course already exists and cannot be replaced/overwritten
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to course {EvIt.data.Name} already existing.");
}
break;
case "course_enrolled":
// Enroll existing person into existing course
// Check whether course and person exist
existingCourse = Db.Courses.FirstOrDefault(c => c.CourseId == EvIt.StreamId);
if (existingCourse != null)
{
existingPerson = Db.Persons.FirstOrDefault(p => p.PersonId == EvIt.data.PersonId);
if (existingPerson != null)
{
// Make sure that enrollment does not already exist
var existingCourseEnrolled = Db.CoursesEnrolled.FirstOrDefault(ce => ce.CourseId == EvIt.StreamId && ce.PersonId == EvIt.data.PersonId);
if (existingCourseEnrolled == null)
{
// Create a new CourseEnrollment object, populate all properties and save to data structure
var newCourseEnrolled = new CourseEnrolled();
newCourseEnrolled.CourseId = EvIt.StreamId;
newCourseEnrolled.PersonId = (int)EvIt.data.PersonId;
Db.CoursesEnrolled.Add(newCourseEnrolled);
Db.SaveChanges();
// Log that "course_enrolled" event was successfully processed
AddToLog(EvIt.EventId, EvIt.StreamId, $"Successfully processed event '{EvIt.Event}' to enroll person '{existingPerson.Name}' in course '{existingCourse.Name}'.");
}
else
{
// Issue error that course enrollment does already exist
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to course enrollment for person '{existingPerson.Name}' in course '{existingCourse.Name}' already existing.");
}
}
else
{
// Issue error that person does not exist
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to person {EvIt.data.PersonId} not existing.");
}
}
else
{
// Issue error that course does not exist
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to course {EvIt.StreamId} not existing.");
}
break;
case "course_renamed":
// Rename existing course
// First, ensure course to rename exists
existingCourse = Db.Courses.FirstOrDefault(c => c.CourseId == EvIt.StreamId);
if (existingCourse != null)
{
if (EvIt.data.Name != null)
{
// Course exists and can be renamed. Save new name to data structure.
string existingCourseName = existingCourse.Name;
existingCourse.Name = EvIt.data.Name;
Db.SaveChanges();
// Log that "course_renamed" event was successfully processed
AddToLog(EvIt.EventId, EvIt.StreamId, $"Successfully processed event '{EvIt.Event}' to rename course '{existingCourseName}' to '{EvIt.data.Name}'.");
}
else
{
// Issue error that new course name was not provided
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to missing course name.");
}
}
else
{
// Issue error that course to rename does not exist
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to course {EvIt.StreamId} not existing.");
}
break;
case "course_disenrolled":
// Unenroll person from course
// First, ensure enrollment record exists
var existingCourseEnrolled2 = Db.CoursesEnrolled.FirstOrDefault(ce => ce.CourseId == EvIt.StreamId && ce.PersonId == EvIt.data.PersonId);
if (existingCourseEnrolled2 != null)
{
// Remove enrollment record from database
Db.CoursesEnrolled.Remove(existingCourseEnrolled2);
Db.SaveChanges();
// Log that "course_disenrolled" event was successfully processed
AddToLog(EvIt.EventId, EvIt.StreamId, $"Successfully processed event '{EvIt.Event}' to unenroll person {EvIt.data.PersonId} from course {EvIt.StreamId}.");
}
else
{
// Issue error that course enrollment does not exist
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to course enrollment for course {EvIt.StreamId} and person {EvIt.data.PersonId} not existing.");
}
break;
case "person_renamed":
// Rename existing person
// First, ensure person exists, and new name has been provided; if so, overwrite name
existingPerson = Db.Persons.FirstOrDefault(p => p.PersonId == EvIt.StreamId);
if (existingPerson != null && EvIt.data.Name != null && EvIt.data.Name != "")
{
// Save new name and save data to data structure
string existingPersonName = existingPerson.Name;
existingPerson.Name = EvIt.data.Name;
Db.SaveChanges();
// Log that "person_renamed" event was successfully processed
AddToLog(EvIt.EventId, EvIt.StreamId, $"Successfully processed event '{EvIt.Event}' to rename person '{existingPersonName}' to '{EvIt.data.Name}'.");
}
else
{
// Person does not exist or name not provided: cannot rename, issue appropriate error
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' due to person {EvIt.StreamId} not existing or person name not provided.");
}
break;
default:
// Log that event could not be processed, because it has no code handler
AddToLog(EvIt.EventId, EvIt.StreamId, $"Could not process event '{EvIt.Event}' because no handler exists for it.");
break;
}
}
