IsContactAssociatedWithWebRole

/// <summary>
/// Checks whether a contact is already associated with a specific web role.
/// </summary>
public bool IsContactAssociatedWithWebRole(IOrganizationService service, Guid contactId, Guid webRoleId)
{
    QueryExpression associationCheck = new QueryExpression("adx_webrole_contact")
    {
        ColumnSet = new ColumnSet(false), // No need to retrieve columns
        Criteria = new FilterExpression
        {
            Conditions =
    {
        new ConditionExpression("contactid", ConditionOperator.Equal, contactId),
        new ConditionExpression("adx_webroleid", ConditionOperator.Equal, webRoleId)
    }
        }
    };

    return service.RetrieveMultiple(associationCheck).Entities.Count > 0;
}