Question

i’m working on a small project that is supposed to allow basic searches of the database.
Currently i’m using nhibernate for the database interaction.
In the database i have 2 tables: Person and Address. The Person table has a many-to-one relationship with Address.

The code i’ve come up with for doing searches is:

public IList<T> GetByParameterList(List<QueryParameter> parameterList)
    {
        if (parameterList == null)
        {
            return GetAll();
        }
        using (ISession session = NHibernateHelper.OpenSession())
        {
            ICriteria criteria = session.CreateCriteria<T>();
            foreach (QueryParameter param in parameterList)
            {
                switch (param.Constraint)
                {
                    case ConstraintType.Less:
                        criteria.Add(Expression.Lt(param.ParameterName, param.ParameterValue));
                        break;
                    case ConstraintType.More:
                        criteria.Add(Expression.Gt(param.ParameterName, param.ParameterValue));
                        break;
                    case ConstraintType.LessOrEqual:
                        criteria.Add(Expression.Le(param.ParameterName, param.ParameterValue));
                        break;
                    case ConstraintType.EqualOrMore:
                        criteria.Add(Expression.Ge(param.ParameterName, param.ParameterValue));
                        break;
                    case ConstraintType.Equals:
                        criteria.Add(Expression.Eq(param.ParameterName, param.ParameterValue));
                        break;
                    case ConstraintType.Like:
                        criteria.Add(Expression.Like(param.ParameterName, param.ParameterValue));
                        break;
                }
            }

            try
            {
                IList<T> result = criteria.List<T>();
                return result;
            }
            catch
            {
                //TODO: Implement some exception handling
                throw;
            }
        }
    }

The query parameter is a helper object that i use to create criterias and send it to the dal, it looks like this:

public class QueryParameter
{
    public QueryParameter(string ParameterName, Object ParameterValue, ConstraintType constraintType)
    {
        this.ParameterName = ParameterName;
        this.ParameterValue = ParameterValue;
        this.Constraint = constraintType;
    }

    public string ParameterName
    {
        get;
        set;
    }

    public Object ParameterValue
    {
        get;
        set;
    }

    public ConstraintType Constraint
    {
        get;
        set;
    }
}

Now this works well if i’m doing a search like FirstName = “John” , but not when i try to give a parameter like Street = “Some Street”. It seems that nhibernate is looking for a street column in the Person table but not in the Address table.

Any idea on how should i change my code for so i could do a proper search? Tips? Maybe some alternatives?

Disclaimer: i’m kind of a noob so please be gentle 😉
Thanks, Denis.

Answer 1

It is looking for the Street property in the Person entity (notice ORM language… there are no tables and columns ;-)) because of this line:

ICriteria criteria = session.CreateCriteria<T>();

I assume that your type T is Person, and so your criteria assumes that the constraints that you are adding refer to properties in Person.

If you pass in a parameter that you know is a filter on the Address entity, you need to call CreateAlias(...) to “join” to the Address.