/*
* FYI,
*
* ref: https://blogs.msdn.microsoft.com/marcelolr/2010/07/16/optimistic-and-pessimistic-concurrency-a-simple-explanation/
*/
public static void OptimisticConcurrency()
{
Console.WriteLine("*** OptimisticConcurrency Starts ***");
Student student = null;
using (var context = new SchoolDBEntities())
{
student = context.Students.First();
}
//Edit student name
student.StudentName = "Robin";
using (var context = new SchoolDBEntities())
{
context.Database.Log = Console.Write;
try
{
context.Entry(student).State = EntityState.Modified;
context.SaveChanges();
Console.WriteLine("Student saved successfully.");
}
catch (DbUpdateConcurrencyException ex)
{
Console.WriteLine("Concurrency Exception Occurred.");
}
}
Console.WriteLine("*** OptimisticConcurrency Ends ***");
}
public static void ExplicitLoading()
{
Console.WriteLine("*** ExplicitLoading Starts ***");
using (var context = new SchoolDBEntities())
{
context.Database.Log = Console.Write;
Student std = context.Students
.Where(s => s.StudentID == 1)
.FirstOrDefault <Student>();
//Loading Standard for Student (seperate SQL query)
context.Entry(std).Reference(s => s.Standard).Load();
//Loading Courses for Student (seperate SQL query)
context.Entry(std).Collection(s => s.Courses).Load();
}
Console.WriteLine("*** ExplicitLoading Ends ***");
}
public static void SetEntityState()
{
Console.WriteLine("*** SetEntityState Starts ***");
var student = new Student()
{
StudentID = 1, // root entity with key
StudentName = "Bill",
StandardId = 1,
Standard = new Standard() //Child entity (with key value)
{
StandardId = 1,
StandardName = "Grade 1"
},
Courses = new List <Course>()
{
new Course()
{
CourseName = "Machine Language"
}, //Child entity (empty key)
new Course()
{
CourseId = 2
} //Child entity (with key value)
}
};
using (var context = new SchoolDBEntities())
{
context.Entry(student).State = EntityState.Modified;
foreach (var entity in context.ChangeTracker.Entries())
{
Console.WriteLine("{0}: {1}", entity.Entity.GetType().Name, entity.State);
}
}
Console.WriteLine("*** SetEntityState Ends ***");
}
public static void EntityEntry()
{
Console.WriteLine("*** EntityEntry Starts ***");
using (var context = new SchoolDBEntities())
{
//get student whose StudentId is 1
var student = context.Students.Find(5);
//edit student name
student.StudentName = "Monica";
//get DbEntityEntry object for student entity object
var entry = context.Entry(student);
//get entity information e.g. full name
Console.WriteLine("Entity Name: {0}", entry.Entity.GetType().FullName);
//get current EntityState
Console.WriteLine("Entity State: {0}", entry.State);
Console.WriteLine("********Property Values********");
foreach (var propertyName in entry.CurrentValues.PropertyNames)
{
Console.WriteLine("Property Name: {0}", propertyName);
//get original value
var orgVal = entry.OriginalValues[propertyName];
Console.WriteLine(" Original Value: {0}", orgVal);
//get current values
var curVal = entry.CurrentValues[propertyName];
Console.WriteLine(" Current Value: {0}", curVal);
}
}
Console.WriteLine("*** EntityEntryDemo Ends ***");
}
