Question

Please excuse my ignorance when asking this question as I am still learning NHibernate and Linq. I did some searching around but I do not understand how or if the solution to my question is possible

I have the following block of code:

// this function searches the database's table for a single object that matches the 'Name' property with 'objectName'
public static Object Read<T>(string objectName)
{
    using (ISession session = NHibernateHelper.OpenSession())
    {
        IQueryable<T> objectList = session.Query<T>(); // pull (query) all the objects from the table in the database
        int count = objectList.Count(); // return the number of objects in the table
        // alternative: int count = makeList.Count<T>();

        IQueryable<T> objectQuery = null; // create a reference for our queryable list of objects
        object foundObject = null; // create an object reference for our found object

        if (count > 0)
        {
            // give me all objects that have a name that matches 'objectName' and store them in 'objectQuery'
            objectQuery = (from obj in objectList where obj.Name == objectName select obj);

            // make sure that 'objectQuery' has only one object in it
            try
            {
                foundObject = objectQuery.Single();
            }
            catch
            {
                return null;
            }

            // output some information to the console (output screen)
            Console.WriteLine("Read Make: " + foundObject.ToString());
        }
        // pass the reference of the found object on to whoever asked for it
        return foundObject;
    }
}

This is all great with the exception of one line:
objectQuery = (from obj in objectList where obj.Name == objectName select obj);

The issue here is that I am asking for the “Name” property of an unknown object and that is not only impossible but also erroneous code.

What I’d really like to do here is specify that I am looking for items that have a property belonging to the T-type object.

Any takers?

Answer 1

The problem is that you are writing a generic method, which implies it will accept any type T. But in fact, when you write:

where obj.Name == objectName

you are expecting a particular type, or a type that implements a specific interface, or is derived from a particular base class.

Your method should look more like:

public static T Read<T>(string objectName)
where T : ISomeInterface

Note that I have also changed the return type from Object to T, which is more friendly to the caller of this method and avoids the need for them to cast Object to T.