Duplicate Detection Plugin code for Microsoft dynamics CRM

 using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using Microsoft.Xrm.Sdk;

using System.ServiceModel;

using Microsoft.Xrm.Sdk.Query;

namespace MyPlugins

{

    public class DuplicateCheck : IPlugin

    {

        public void Execute(IServiceProvider serviceProvider)

        {

            // Extract the tracing service for use in debugging sandboxed plug-ins.  

            // If you are not registering the plug-in in the sandbox, then you do  

            // not have to add any tracing service related code.  

            ITracingService tracingService =

                (ITracingService)serviceProvider.GetService(typeof(ITracingService));

            // Obtain the execution context from the service provider.  

            IPluginExecutionContext context = (IPluginExecutionContext)

                serviceProvider.GetService(typeof(IPluginExecutionContext));

            // Obtain the organization service reference which you will need for  

            // web service calls.  

            IOrganizationServiceFactory serviceFactory =

                (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));

            IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);

            // The InputParameters collection contains all the data passed in the message request.  

            if (context.InputParameters.Contains("Target") &&

                context.InputParameters["Target"] is Entity)

            {

                // Obtain the target entity from the input parameters.  

                Entity contact = (Entity)context.InputParameters["Target"];

                try

                {

                    // Plug-in business logic goes here.  

                    string email = string.Empty;

                    if (contact.Attributes.Contains("emailaddress1"))

                    {

                        email = contact.Attributes["emailaddress1"].ToString();

                        // select * from contact where emailaddress1 == 'email'

                        QueryExpression query = new QueryExpression("contact");

                        query.ColumnSet = new ColumnSet(new string[] { "emailaddress1" });

                        query.Criteria.AddCondition("emailaddress1", ConditionOperator.Equal, email);

                        EntityCollection collection = service.RetrieveMultiple(query);

                        if(collection.Entities.Count > 0)

                        {

                            throw new InvalidPluginExecutionException("Contact with email already exists!!!");

                        }

                    }

                }

                catch (FaultException<OrganizationServiceFault> ex)

                {

                    throw new InvalidPluginExecutionException("An error occurred in MyPlug-in.", ex);

                }

                catch (Exception ex)

                {

                    tracingService.Trace("MyPlugin: {0}", ex.ToString());

                    throw;

                }

            }

        }

    }

}