private static void UpdateExample2()
{
// For example, we got a student change request from UI
// User changed the student with ID = 1 and sent us the object
var studentFromGui = new Student()
{
FirstName = "User changed first name",
LastName = "User changed last name",
Id = 1
};
// We need to update student with ID = 1 with the new data
using (var db = new UniversityDb(ConnectionString))
{
// One way... not so practical (check update example 3 for better approach):
// We are using .First this time... maybe we want the exception
// if user was changing non existing student
var studentFromDb = db.Students.First(s => s.Id == studentFromGui.Id);
studentFromDb.FirstName = studentFromGui.FirstName;
studentFromDb.LastName = studentFromGui.LastName;
// ...
db.SaveChanges();
// What if we add a new property to student? we have to remember to update
// this method as well. And you will forget :)
}
}
static void Main(string[] args)
{
var dbContext = new UniversityDb();
Database.SetInitializer(new MigrateDatabaseToLatestVersion <UniversityDb, Configuration>());
dbContext.Database.CreateIfNotExists();
//Seed
var databases = new Course
{
Id = 1,
Name = "Databases",
Description = "malko e tegavo"
};
var iliyan = new Student
{
Name = "Iliyan",
Number = 111,
Courses = new HashSet <Course>()
{
databases
}
};
dbContext.Courses.Add(databases);
dbContext.Students.Add(iliyan);
dbContext.SaveChanges();
}
private static void DeleteExample1()
{
using (var db = new UniversityDb(ConnectionString))
{
var studentToRemove = db.Students.LastOrDefault();
if (studentToRemove != null)
{
db.Students.Remove(studentToRemove);
db.SaveChanges();
}
}
}
private static void UpdateExample1()
{
using (var db = new UniversityDb(ConnectionString))
{
// or shorter: .FirstOrDefault(s => s.Mentor != null)
var student = db.Students.Where(s => s.Mentor != null).FirstOrDefault();
if (student != null)
{
student.FirstName = "Hehe";
db.SaveChanges();
}
}
}
private static void ReadExample1()
{
using (var db = new UniversityDb(ConnectionString))
{
// But why is the students mentoring list null?!
List <Professor> professors = db.Professors.Where(p => p.StudentsMentoring.Count == 1).ToList();
// Database operations can be expensive,
// if we want to fetch additional items from the database, we have to be explicit.
List <Professor> professors2 = db.Professors.Where(p => p.StudentsMentoring.Count == 1)
.Include(p => p.StudentsMentoring)
.Include(p => p.CoursesLecturing)
.ToList();
}
}
private static void UpdateExample3()
{
var studentFromGui = new Student()
{
FirstName = "User changed first name again",
LastName = "User changed last name again",
Id = 1
};
using (var db = new UniversityDb(ConnectionString))
{
// Mark entry as modified. Context will start tracking it.
db.Entry(studentFromGui).State = EntityState.Modified;
// Let EF update everything...
db.SaveChanges();
}
}
private static void SaveExample2()
{
using (var db = new UniversityDb(ConnectionString))
{
try
{
var pero = new Student();
db.Students.Add(pero);
db.SaveChanges();
}
catch (DbEntityValidationException)
{
// Calling at this point will cause DbEntityValidationException
// We tried to save a student without first name and last name set
// (marked as required)
}
}
}
private static void SaveExample3()
{
using (var db = new UniversityDb(ConnectionString))
{
var ivica = new Professor()
{
LastName = "Boticki",
FirstName = "Ivica"
};
var lovro = new Student()
{
FirstName = "Lovro",
LastName = "Lovric",
Mentor = ivica
};
db.Students.Add(lovro);
db.SaveChanges();
}
}
private static void SaveExample1()
{
using (var db = new UniversityDb(ConnectionString))
{
var ivan = new Student()
{
FirstName = "Ivan",
LastName = "Horvat"
};
db.Students.Add(ivan);
// Save changes is a required step which actually
// pushes changes to the database.
//
// Usually you want to use SaveChangesAsync() variant
db.SaveChanges();
// Ivan.Id before SaveChanges() => 0
// Ivan.Id after SaveChanges() => 1...N
}
}
public StudentController()
{
_universityDb = new UniversityDb();
}
