Fluent Nhibernate List<string> mapping

Question

I have a simple class with a IList<string> property. How to map this property in Fluent Nhibernate ?

[Serializable]
public class ExportTask
{
    private IList<string> _csvExportList = new List<string>();

    public ExportTask()
    {}

    public virtual IList<string> CsvExportList
    {
        get { return _csvExportList; }
        set { _csvExportList = value; }
    }
}

public class ExportTaskMap : SubclassMap<ExportTask>
{
    public ExportTaskMap()
    {           
        HasMany(x => x.CsvExportList)
               .Element("CsvExportList")
               .Cascade
               .AllDeleteOrphan();
    }
}

Following error occurs:

Initializing -failed to lazily initialize a collection of role: MyApp.Tasks.ExportTask.CsvExportList, no session or session was closed

When calling addrange on the collection:

var exportList = new List<string>()
                     {
                        {"item1"},
                        {"item2"}
                      };

CsvExportList.AddRange(exportList);

jero2rome · Accepted Answer · 2014-10-01 08:40:32Z

6

It truns out we can use AsList mapping with a column for the list index and allworks great. I wonder why there are no answers out there for this simple usecase. Hope it helps out someone.

public class ExportTaskMap : SubclassMap<ExportTask>
{
  public ExportTaskMap()
  {           
     HasMany(x => x.CsvExportList)
           .Element(@"CsvProperty")
           .KeyColumn(@"ExportTask_id")
           .Table(@"CsvExportProperties")
           .AsList(x => x.Column(@"CsvPropertyListIndex"))
           .Not.LazyLoad();
  }
}

And the mapped table will look like the following in the database.

enter image description here

answered Oct 1, 2014 at 8:40

jero2rome

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2 Comments

Rafi Over a year ago

This doesn't work with an IList<SomeObject> but only with IList<string>, any idea why? The index column is always null.

jero2rome Over a year ago

You cannot use this style of mapping to map a list of objects. There are other ways to do it.

Community · Accepted Answer · 2017-05-23 12:07:31Z

0

Would be helpful to see the error you get, but one thing seems to be obvious: you are missing setter of the IList<string> CsvExportList. So, mapping should target the field

HasMany<string>(Reveal.Property<string>("_csvExportList"))

Check these how to handle field mapping:

Or change your IList<string> to have at least protected setter (I personally would go this way) and remove the readonly setting.

private IList<string> _csvExportList;
public virtual IList<string> CsvExportList
{
    get { return _csvExportList ?? (_csvExportList = new List<string>(); }
    protected set { _csvExportList = value; }
}

These are hints, the exception or error you get could tell us more

edited May 23, 2017 at 12:07

CommunityBot

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answered Sep 24, 2014 at 13:23

Radim Köhler

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2 Comments

jero2rome Over a year ago

Added additional error message. HasMany<string>(Reveal.Property<string>("_csvExportList")) couldn't be used since the syntax results in error. Also, couldn't have a setter since, readonly fields cannot have setter. I use Add() and AddRange() methods to fill the collection.

Radim Köhler Over a year ago

Honestly... I did not see the readonly. Why is it there? This does not make sense to me, it only brings you issues. If you want to hide the CsvExportList to any upper layer, hide its setter (make it protected). That's enough. And the error you get is related to fact, that you are working with the entity ExportTask once the session is closed. You have to extend the lifetime of that session or eagerly load that collection... BUT I would go with protected setter for sure...

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