NHibernate component mapping – Null Component

fluent-nhibernatenhibernate

I have a mapped entity, Matter, that has a mapped component, Injury.

The only property on the Injury is DateOfInjury which is a nullable datetime.

When I retrieve the Matter, if the DateOfInjury is null, the component is null.

Thus something like this matter.Injury.DateOfInjury will throw.

Could someone explain if I am doing something obvious to cause this behaviour?

I would have expected that the Injury component gets initialized by nHibernate as an object and that the DateOfinjury property is null.

This would be more flexible i would think?

Best Solution

I think that's the default behavior for a component mapping. The NHibernate docs for component say that if all elements of the component are null, the component itself will just be null.

If you only have a single property in the component, it might make sense to just map it as a nullable DateTime property on the Matter class.

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NHibernate dynamic mapping

Take a look at the new Mapping By Code functionality of NH 3.2. It should make it easy to create new table definitions at runtime. In contrast to Fluent, you don't need to write a mapping class, you just can add new classes in for loops:

// lookup all dynamic tables in the database using SQL or SMO or whatever
var dynamicTables = GetDynamicTables();

// map all dynamic tables
foreach(var table in dynamicTables)
{
  mapper.Class<MyGenericEntity>(ca =>
  {
      // use an entity name to distinguish the mappings.
      ca.EntityName(table.Name);
      ca.Id(x => x.Id, map =>
      {
          map.Column("Id");
          map.Generator(Generators.HighLow, gmap => gmap.Params(new { max_low = 100 }));
      });
      // map properties, using what ever is required: if's, for's ...
      ca.Property(x => x.Something, map => map.Length(150));
  });
}

Using the entity name you can store and load the entities to and from different tables, even if they are mapped as the same entity class. It is like Duck Typing With NHibernate..

Believe me, it won't be easy. If you are interested in a big challenge which impresses every NH expert, just go for it. If you just want to get it working you should choose a more classic way: create a static database model which is able to store dynamic data in a generic way (say: name value pairs).

Best Solution

Related Solutions

NHibernate dynamic mapping

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