1. Create a new public class called EmailDataAccessLayerQueryExpression in the DataAccessLayer folder that inherits from BaseDataAccessLayer and implements IEmailDataAccessLayer:

public class EmailDataAccessLayerQueryExpression : BaseDataAccessLayer, IEmailDataAccessLayer 

2. Add the following using statements to the default ones:

using Microsoft.Xrm.Sdk; 
using Packt.Xrm.Entities; 
using Microsoft.Xrm.Sdk.Query; 
using Microsoft.Crm.Sdk.Messages; 

3. Create a constructor that takes IOrganizationService and calls the base constructor:

public EmailDataAccessLayerQueryExpression(IOrganizationService organizationService) : base(organizationService) 

4. Override the UpdateEntity method to use OrganizationService:

public override void UpdateEntity(Entity entity) 
{ 
    OrganizationService.Update(entity); 
} 

5. Override the Commit method to have no implementation:

public override void Commit() 
{ 
} 

6. Implement the CloseEmailAsCancelled method to use OrganizationService:

public void CloseEmailAsCancelled(Email email) 
{ 
    email.StateCode = EmailState.Canceled; 

    var setStateRequest = new SetStateRequest() 
    { 
       Status = new OptionSetValue((int)email_statuscode.Canceled), 
       State = new OptionSetValue((int)EmailState.Canceled), 
       EntityMoniker = new EntityReference(Email.EntityLogicalName, 
          email.Id) 
    }; 
    OrganizationService.Execute(setStateRequest); 
} 

7. Implement the GetEmails method to use QueryExpression:

public IEnumerable<Email> GetEmails(Guid parentEntityId) 
{ 
    var queryExpression = new QueryExpression() 
    { 
        EntityName = Email.EntityLogicalName, 
        ColumnSet = new ColumnSet( "subject"), 
        Criteria = 
        { 
            Filters = 
                { 
                    new FilterExpression 
                    { 
                        FilterOperator = LogicalOperator.And, 
                        Conditions = 
                        { 
                            new ConditionExpression("regardingobjectid", ConditionOperator.Equal, parentEntityId), 
                            new ConditionExpression("statecode", ConditionOperator.Equal, (int)EmailState.Open) 
                        }, 
                    } 
                } 
        } 
    }; 

    var entityCollection = OrganizationService.RetrieveMultiple(queryExpression); 
    return entityCollection.Entities.Select(e => e.ToEntity<Email>()).ToList(); 
} 

8. Update the GetEmailDataAccessLayer method in DataAccessLayerFactory to return an instance of the newly created EmailDataAccessLayerQueryExpression object:

public IEmailDataAccessLayer GetEmailDataAccessLayer() 
{ 
    if (_emailDataAccessLayer == null) 
        _emailDataAccessLayer = new EmailDataAccessLayerQueryExpression(_organisationService); 

    return _emailDataAccessLayer; 
}