How to enumerate column names with NHibernate?

Question

I've got a class with a bunch of [ColumnName("foo")] NHibernate attributes. Is there an easy way to ask NHibernate to list all of the ColumnNames for a given class?

It sounds like it should be really easy but I'm just not seeing any kind of inspection in the NHibernate docs (or maybe I'm just blind today).

Answer 1

I had this same problem, but found IClassMetadata doesn't have any column information, just property types, names, identifier, and table information.

What worked for me:

PersistentClass persistentClass = cfg.GetClassMapping(typeof(MyEntity));
Property property = persistentClass.GetProperty(propertyName);
property.ColumnIterator   // <-- the column(s) for the property

Answer 2

How to get the database column names for an entity mapped by NHibernate:

using System;
using System.Collections.Generic;
using NHibernate;
using NHibernate.Persister.Entity;

namespace Stackoverflow.Example
{
    /// <summary>
    /// NHibernate helper class
    /// </summary>
    /// <remarks>
    /// Assumes you are using NHibernate version 3.1.0.4000 or greater (Not tested on previous versions)
    /// </remarks>
    public class NHibernateHelper
    {
        /// <summary>
        /// Gets the list of database column names for an entity
        /// </summary>
        /// <param name="sessionFactory">NHibernate SessionFactory</param>
        /// <param name="entity">A mapped entity</param>
        /// <returns>List of column names</returns>
        public static IEnumerable<string> GetPropertyColumnNames(ISessionFactory sessionFactory, object entity)
        {
            Type entityType = entity == null ? null : entity.GetType();

            List<string> columnNameList = null;

            // This has some cool methods and properties so check it out
            var metaData = entityType == null ? null : sessionFactory.GetClassMetadata(entityType.ToString());

            //- metaData validity check ... will be null if provided type is not mapped
            if (metaData != null)
            {
                // This has some even cooler methods and properties so definitely check this out
                var entityPersister = (AbstractEntityPersister) metaData;

                //- how to get the entity's identifier
                //- string entityIdentifier = metaData.IdentifierPropertyName;

                //- Get the database identifier
                //- can have multiple in case of composite keys
                IEnumerable<string> dbIdentifierNameList = entityPersister.KeyColumnNames;

                var propertyNameList = entityPersister.PropertyNames;

                // Adding the database identifier first
                columnNameList = new List<string>(dbIdentifierNameList);
                //- then add properties column names
                foreach (var propertyName in propertyNameList)
                {
                    var columnNameArray = entityPersister.GetPropertyColumnNames(propertyName);
                    columnNameList.AddRange(columnNameArray.Where(columnName => dbIdentifierNameList.Contains(columnName) == false));
                }
            }

            return columnNameList;
        }
    }
}   

Usage:

// Get your NHiberate SessionFactory wherever that is in your application
var sessionFactory = NHibernateHelper.SessionFactory;

// Get an entity that you know is mapped by NHibernate
var customer = new Customer();

// Get a list of the database column names for the entity
var columnNames = 
        Stackoverflow.Example.NHibernateHelper.GetPropertyColumnNames( sessionFactory, customer );

Bask in the glory of this awesomeness :)