NHibernate: Add criteria if param not null

Question

I'm trying to retrieve a list of orders based on parameters specified by a user (basic search functionality). The user will enter either an orderId or a bunch of other params, those will get wrapped up into a message, and eventually make their way to the method below. My question is, how do I only look at the parameters that actually have values? So if a user were to enter a received date range and a store number and all other fields were null, I want to return orders for stores received in the date range and ignore all the null parameters. At first I was thinking I could use a conjunction, but I can't see a way to ignore the null parameters. Then I started splitting things out into the if statements below the main expression, but I don't want to look at those criteria if the user provides an externalId. Is there a simple way to do this?

        public IList<Core.Order> GetOrderByCriteria
        (
        string ExternalId,
        int? Store,
        int? Status,
        DateTime? beforeTransmissionDate, DateTime? afterTransmissionDate,
        DateTime? beforeAllocationProcessDate, DateTime? afterAllocationProcessDate,
        DateTime? beforeReceivedDate, DateTime? afterReceivedDate
        )
    {
        try
        {
            NHibernate.ICriteria criteria = NHibernateSession.CreateCriteria(typeof(Core.Order))
                .Add(Expression.Or
                        (
                        Expression.Like("ExternalId", ExternalId),
                        Expression.Conjunction()
                            .Add(Expression.Between("ReceivedDate", beforeReceivedDate, afterReceivedDate))
                            .Add(Expression.Between("TransmissionDate", beforeTransmissionDate, afterTransmissionDate))
                            .Add(Expression.Between("AllocationProcessDate", beforeAllocationProcessDate, afterAllocationProcessDate))
                        )
                     );

            if(Store.HasValue)
                criteria.Add(Expression.Eq("Status", Status));

            if(Status.HasValue)
                criteria.Add(Expression.Eq("Store", Store));


            return criteria.List<Core.Order>();
        }
        catch (NHibernate.HibernateException he)
        {
            DataAccessException dae = new DataAccessException("NHibernate Exception", he);
            throw dae;
        }
    }

Answer 1

I had to do something similar not long ago. I'm pretty sure you can modify this to fit your needs.

    private ICriteria AddSearchCriteria(ICriteria criteria, string fieldName, string value)
    {

        if (string.IsNullOrEmpty(fieldName))
            return criteria;

        if(string.IsNullOrEmpty(value))
            return criteria;

        criteria.Add(Expression.Like(fieldName, "%" + value + "%"));

        return criteria;
    }

The code calling the method ended up looking like this:

var query = session.CreateCriteria(typeof (User));

AddSearchCriteria(query, "FirstName", form["FirstName"]);
AddSearchCriteria(query, "LastName", form["LastName"]);

var resultList = new List<User>();
query.List(resultList);
return resultList;

Leave it up to the function to determine if the input is valid and whether to return the unmodified ICriteria or to add another Expression before returning it.

Answer 2

I wound up dropping the whole conjunction thing and replacing the code in the try block with the code below. I also used joins which reduced the number of db accesses and reduced the amount of code needed.

NHibernate.ICriteria criteria = NHibernateSession.CreateCriteria(typeof(Core.Order));

            if (!String.IsNullOrEmpty(ExternalId))
            {
                criteria.Add(Expression.Like("ExternalId", ExternalId));
            }

            if (beforeReceivedDate != null && afterReceivedDate != null)
                criteria.Add(Expression.Between("ReceivedDate", beforeReceivedDate, afterReceivedDate));

            if (beforeTransmissionDate != null && afterTransmissionDate != null)
                criteria.Add(Expression.Between("TransmissionDate", beforeTransmissionDate, afterTransmissionDate));

            if (beforeAllocationProcessDate != null && afterAllocationProcessDate != null)
                criteria.Add(Expression.Between("AllocationProcessDate", beforeAllocationProcessDate, afterAllocationProcessDate));

            if (Store.HasValue)
                criteria.CreateCriteria("Store", "Store").Add(Expression.Eq("Store.LocationNumber", Store.Value));

            return criteria.List<Core.Order>();