R – How to Map Two Tables To One Class in Fluent NHibernate

fluent-nhibernatenhibernatenhibernate-mapping

I am having a problem with fluent nhiberbate mapping two tables to one class.

I have the following database schema:

TABLE dbo.LocationName
(
  LocationId INT PRIMARY KEY,
  LanguageId INT PRIMARY KEY,
  Name VARCHAR(200)
)

TABLE dbo.Language
(
  LanguageId INT PRIMARY KEY,
  Locale CHAR(5)
)

And want to build the following class definition:

public class LocationName 
{
      public virtual int LocationId { get; private set; }
      public virtual int LanguageId { get; private set; }
      public virtual string Name { get; set; }
      public virtual string Locale { get; set; } 
}

Here is my mapping class:

  public LocalisedNameMap()
  {
     WithTable("LocationName");
     UseCompositeId()
        .WithKeyProperty(x => x.LanguageId)
        .WithKeyProperty(x => x.LocationId);
     Map(x => x.Name);

     WithTable("Language", lang =>
                             {
                                lang.WithKeyColumn("LanguageId");
                                lang.Map(x => x.Locale);
                             });
  }

The problem is with the mapping of the Locale field being from another table, and in particular that the keys between those tables don't match. Whenever I run the application with this mapping I get the following error on startup:

Foreign key
(FK7FC009CCEEA10EEE:Language
[LanguageId])) must have same number
of columns as the referenced primary
key (LocationName [LanguageId,
LocationId])

How do I tell nHibernate to map from LocationName to Language using only the LanguageId field?

Best Answer

You can use , don't know the name in FNH, to denormalize a class, that is, bring in a column from another table. See http://ayende.com/blog/3961/nhibernate-mapping-join

Related Solutions

Fluent NHibernate: How to create one-to-many bidirectional mapping

To get a bidirectional association with a not-null foreign key column in the Details table you can add the suggested Owner property, a References(...).CanNotBeNull() mapping in the DetailsMap class, and make the Summary end inverse.

To avoid having two different foreign key columns for the two association directions, you can either specify the column names manually or name the properties in a way that gives the same column name for both directions. In this case you I suggest renaming the Details.Owner property to Details.Summary.

I made the Summary id generated by increment to avoid problems when inserting into the table since Summary currenty has no columns besides id.

Domain:

public class Detail
{
    public int id { get; protected set; }
    public string ItemName { get; set; }

    // Renamed to use same column name as specified in the mapping of Summary.Details
    public Summary Summary {get; set;} 
}

public class Summary
{
    public Summary()
    {
        Details = new List<Detail>();
    }

    public int id { get; protected set; }
    public IList<Detail> Details { get; protected set; }
}

Mapping:

public class DetailMap : ClassMap<Detail>
{
    public DetailMap()
    {
        Id(x => x.id)
            .GeneratedBy.Native();

        Map(x => x.ItemName)
            .CanNotBeNull();

        References<Summary>(x => x.Summary)
            // If you don't want to rename the property in Summary,
            // you can do this instead:
            // .TheColumnNameIs("Summary_id")
            .CanNotBeNull();
    }
}

public class SummaryMap : ClassMap<Summary>
{
    public SummaryMap()
    {
        Id(x => x.id)
            .GeneratedBy.Increment();

        HasMany<Detail>(x => x.Details)
            .IsInverse()
            .AsBag(); // Use bag instead of list to avoid index updating issues
    }
}

R – Fluent NHibernate question

What you're looking for is a of a set of elements, which in standard hbm mapping is:

<set name="Roles" table="UserRoles">
  <key column="UserID" />
  <element column="Role" />
</set>

For Fluent NHibernate you can map this like so:

HasMany<string>(x => x.Roles)
  .AsElement("Role");

You may need to also specify the key name using WithKeyColumn(string).

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