NHibernate Criteria - How to filter on combination of properties

Question

I needed to filter a list of results using the combination of two properties. A plain SQL statement would look like this:

SELECT TOP 10 *
FROM Person
WHERE FirstName + ' ' + LastName LIKE '%' + @Term + '%'

The ICriteria in NHibernate that I ended up using was:

ICriteria criteria = Session.CreateCriteria(typeof(Person));
criteria.Add(Expression.Sql(
    "FirstName + ' ' + LastName LIKE ?",
    "%" + term + "%",
    NHibernateUtil.String));
criteria.SetMaxResults(10);

It works perfectly, but I'm not sure if it is the ideal solution since I'm still learning about NHibernate's Criteria API. What are the recommended alternatives?

• Is there something besides Expression.Sql that would perform the same operation? I tried Expression.Like but couldn't figure out how to combine the first and last names.
• Should I map a FullName property to the formula "FirstName + ' ' + LastName" in the mapping class?
• Should I create a read only FullName property on the domain object then map it to a column?

Exploiter

Answer 1

You can do one of the following:

• If you always work with the full name, it's probably best to have a single property
• Create a query-only property for that purpose (see http://ayende.com/Blog/archive/2009/06/10/nhibernate-ndash-query-only-properties.aspx)
• Do the query in HQL, which is better suited for free-form queries (it will probably be almost the same as your SQL)
• Use a proper entity-based Criteria:

---

Session.CreateCriteria<Person>()
       .Add(Restrictions.Like(
            Projections.SqlFunction("concat",
                                    NHibernateUtil.String,
                                    Projections.Property("FirstName"),
                                    Projections.Constant(" "),
                                    Projections.Property("LastName")),
            term,
            MatchMode.Anywhere))

Linesman

Query-only - how very useful, didn't know about that option. Seems like I learn something new every day in NHibernate. Thanks for the Projections code sample too. – Exploiter

Answer 2

On the pure technical side i don't have an answer, but consider this: since you are only have a single input field for the user to enter the term, you don't know if he is going to enter 'foo bar' or 'bar foo'... so i would recommend this:

ICriteria criteria = Session.CreateCriteria(typeof(Person));
criteria.Add(Expression.Like("FirstName",term, MatchMode.Anywhere) || Expression.Like("LastName",term, MatchMode.Anywhere));
criteria.SetMaxResults(10);

Zenobia

Thanks for the suggestions. Originally I tried that but people were typing in "john smi" and expecting to see John Smith pop up. – Exploiter

I handle this case by looking if there is no space I match against first or last if there is a space I then split the search string and search against the first and last again. – Candor