How to update record using Entity Framework

In previous post How to insert new record using Entity Framework, I discussed one aspect of CRUD operation in an application or process. In this post I will talk about another aspect of the process, how to update a record using Entity Framework. If you are building some kind of business intelligence aplication where only action you have to take is read the data, then you may not be interested in UPDATE part of the process. But most of the applications require you to undertake whole spectrum of operations. And UPDATE is big part of the process.

The process of updating database records using Entity Framework is pretty straight forward. In previous post you saw that you use the collection property of Data Context to add new object in it and then call SaveChanges method. You will still be using SaveChanges method. Only difference is that you are not operating on the collection object. First you will use LINQ query on Data Context to get instance of the record object. Then make the changes to that object and then call SaveChanges. Entity Framework keeps track of what records are being changed when you change any property value of an object. When you call SaveChanges, it prepares a list of objects that need to be updated. And then take appropriate action. All the tracking is transparent to you. The following code snippet shows how you can update record using Entity Framework.

protected void OnUpdate(object sender, EventArgs e)
 {
     if (!ValidateInput())
     {
         ErrorMessage_Label.Visible = true;
         return;
     }

     decimal billRate = 0.0M;
     if (!string.IsNullOrEmpty(BillRate_TextBox.Text.Trim()))
     {
         decimal.TryParse(BillRate_TextBox.Text.Trim(), out billRate);
     }
     var displayName = AntiXss.HtmlEncode(DisplayName_TextBox.Text.Trim());
     if (string.IsNullOrEmpty(displayName))
     {
         displayName = AntiXss.HtmlEncode(FirstName_TextBox.Text.Trim());
         if (!string.IsNullOrEmpty(AntiXss.HtmlEncode(LastName_TextBox.Text.Trim())))
         {
             displayName += string.Format(" {0}", AntiXss.HtmlEncode(LastName_TextBox.Text.Trim()));
         }
     }
     var dataContext = new PMDataContext(Global.ConnectionString);
     var member = (from memberData in dataContext.Members
                   where (memberData.CompanyId == _thisCompany.CompanyId 
                             && memberData.MemberId == _thisMember.MemberId)
                   select memberData).First();

     member.MemberFirstName = AntiXss.HtmlEncode(FirstName_TextBox.Text.Trim());
     member.MemberLastName = AntiXss.HtmlEncode(LastName_TextBox.Text.Trim());
     member.MemberDisplayName = displayName;
     member.Active = _thisMember.Active;
     member.Deleted = _thisMember.Deleted;
     member.BillingRate = billRate;
     member.Availability = Convert.ToInt32(Availability_Dropdown.SelectedValue);

     try
     {
         dataContext.SaveChanges();
     }
     catch (Exception ex)
     {
         // TODO: Log the exception.
         System.Diagnostics.Debug.WriteLine(ex.Message);
     }
}

The implementation gets record for a specified Member using LINQ query. Then updates various values. And at the end calls SaveChanges. Very simple and straightforward process.