Event receiver to block duplicates of same item on Sharepoint List

Question

I have a sharepoint custom list 'Contacts' where items get created.I want to write a event receiver for blocking of duplicate item entry here say name(column of list).

I know this can be achieved by enabling the unique constraint on list.but I need to make a tool/code block.

Can anyone please explain how can I achieve this?

thanks.

Answer 1

There are 10's of examples online stating how to check for duplicates items in a list, which you can change for contact list,

here's an example,

public override void ItemAdding(SPItemEventProperties properties)
   {
       base.ItemAdding(properties);
       if (properties.ListTitle.Equals("Book Massage"))
       {
           try
           {
               using (SPSite thisSite = new SPSite(properties.WebUrl))
               {
                   thisSite.AllowUnsafeUpdates = true;

                   SPWeb thisweb = thisSite.OpenWeb();
                   SPList spList = thisweb.Lists[properties.ListTitle];
                   SPQuery query = new SPQuery();
                   query.Query = @"<Where><Eq><FieldRef Name='Time' /><Value Type='Choise'>" +
                                 properties.AfterProperties["Time"] + "</Value></Eq></Where>";

                   SPQuery query2 = new SPQuery();
                   query2.Query = @"<Where><Eq><FieldRef Name='Date' /><Value Type='Choise'>" +
                                  properties.AfterProperties["Date"] + "</Value></Eq></Where>";

                   SPListItemCollection listItem = spList.GetItems(query);
                   SPListItemCollection listItem2 = spList.GetItems(query2);

                   if (listItem.Count > 0 && listItem2.Count > 0)
                   {
                       properties.Cancel = true;
                       properties.ErrorMessage = "The item exsists braa!";
                   }

               }
           }

For More Information click here