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In a nutshell, how is data-binding performed on a webpage using EF to perform basic CRUD operations? Why is this important?
- Without a single line of code being written, a developer can attach to a database, build a data model based on the database structure (classes), and has all the necessary structures needed to support CRUD operations.
- While EF can do all this without a line of code be written by the developer, it surely generates massive amounts in the code behind, however, it is very organized and structured which creates a clean separation between the data and it's objects (data model classes). Binding ties the UI to the EF either directly or indirectly through business objects. Commonly a GridView is used for this and a few simple CRUD events can be fired through the GridView and then tied to the underlying database using EF, such as with (ie, SelectMethod and ItemType).
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What events are triggered for each of the 4 CRUD events?
- SelectMethod="GridView1_GetData()"
- UpdateMethod="GridView1_UpdateItem()"
- DeleteMethod="GridView1_DeleteItem()"
- InsertMethod="DetailsView1_InsertItem()"
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Write the function for SelectMethod.
- // The return type can be changed to IEnumerable, however to support paging and sorting, the following parameters
- // must be added: int maximumRows, int startRowIndex, out int totalRowCount, string sortByExpression
- public IQueryable<EFGridViewExample.Course> GridView1_GetData()
- {
- // use our EF table and filter, then massage results (order by) using linq
- return new EducationDBEntities().Courses.Where(i => i.Year >= 2010).OrderBy(i => i.Class);
- // several varitations exist on how we want to pull our data and how we want to display it
- // below is a longer way of doing the same thing, first creating our context course table and then
- // poulating it, and then filtering using linq before passing it back to user.
- // var db = new EducationDBEntities().Courses;
- // var result = (from c in db
- // orderby c.Id ascending
- // select c).Take(100);
- //return result;
- }
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Write the function for UpdateMethod.
- public void GridView1_UpdateItem(int id)
- {
- // populate our data model class (course) with the record we found
- var db = new EducationDBEntities();
- EFGridViewExample.Course item = db.Courses.Find(id);
- // make sure we found the error, otherwise display the error to the user
- if (item == null)
- {
- ModelState.AddModelError("", String.Format("Item with id {0} was not found", id));
- return;
- }
- TryUpdateModel(item);
- if (ModelState.IsValid)
- {
- db.SaveChanges();
- GridView1.DataBind();
- }
- }
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Write the function for DeleteMethod.
- public void GridView1_DeleteItem(int id)
- {
- // other slight variations of grabbing the first records exist including: .First(),
- // .FirstOrDefault(), .Single(), .SingleOrDefault(), and .Find(). Find is based on
- // primary key and can perform typically faster than others, ie: var rec = db.Courses.Find(id);
- var db = new EducationDBEntities();
- var course = db.Courses.Where(i => i.Id == id).FirstOrDefault();
- if (course == null)
- {
- ModelState.AddModelError("", String.Format("Item with id {0} was not found", id));
- return;
- }
- else
- {
- db.Courses.Remove(course);
- db.SaveChanges();
- GridView1.DataBind();
- }
- }
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Write the function for InsertMethod.
- // below we use the framework generated values to mesh our values directly to the
- // class EF generated for us. We could have also manually done this using the following:
- // var course = new Course() { Id = 99, Class = "Yoga for Beginners", Year = 2014, Semester = "Fall" };
- public void DetailsView1_InsertItem()
- {
- // initialize a blank course object (strings are null, numeric values 0, virtual table counts 0)
- var course = new EFGridViewExample.Course();
- // mesh the class and the user input together
- TryUpdateModel(course);
- if (ModelState.IsValid)
- {
- // Save changes here
- using (var db = new EducationDBEntities())
- {
- db.Courses.Add(course);
- db.SaveChanges();
- GridView1.DataBind();
- }
- }
- }
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