NHibernate MappingByCode mapping a IDictionary

Question

Tried mapping that with FNH and got into a lot of problems, and eventually found out that FNH is lacking, and not maintained anymore, so i decided to try Nhibernate MappingByCode, which works so far but has no documentation...

I can't find how to map IDictionary

        Map(x => x.EntityDict,
            m =>
            {
                m.Key(k => k.Column("ParentID"));
            },
            km =>
            {
                km.//??ManyToMany
            vm =>
            {
                vm.//??ManyToMany
            }
            );

The options in the km(key mapping) are Element (Value type)/ Component (Inner Object in same table)/ ManyToMany (That i don't really understand in this context)

I Tried using ManyToMany in both because it seems the most logical thing, but it didn't work.

When saving the Dictionary SaveUpdate passed, but it didn't save right to the DB, and couldn't Get the Dictionary back.

Edit: here are sample Dictionary structure

public class Entity1Map : ClassMapping<Entity1>
{
    public Entity1Map()
    {
         Id(x=> x.ID,m=>m.Generator(Generators.Guid));
    }
}

public class Entity2Map : ClassMapping<Entity2>
{
    public Entity2Map()
    {
         Id(x=> x.ID,m=>m.Generator(Generators.Guid));
    }
}


public class Entity3 { public IDictionary<Entity1,Entity2> Dict { get;set; } }
public class Entity3Map : ClassMapping<Entity3>
{
    public Entity3Map()
    {
         Id(x=> x.ID,m=>m.Generator(Generators.Guid));

         //Map Dict??
    }
}

as for table structure -

Entity1 Table : ID Column
Entity2 Table : ID Column
Entity3 Table : ID Column
Dict Table : Entity3_ID,Entity1_ID,Entity2_ID

doesn't have to be this table structure if it is saved and recreated from DB in a different one

@Daniel - here is the hbm

<map name="Targets" table="Dict">
  <key column="Entity3ID" />
  <map-key-many-to-many class="Entity1" column="Entity1ID" />
  <many-to-many class="Entity2" column="Entity2ID" />
</map>

Edit 3 (i think) :

        var entity3 = new Entity3();
        var entity1 = new Entity1();
        var entity2= new Entity2();
        entity3.Dict[entity1] = entity2;

        using (var session = GetSession())
        {
            session.SaveOrUpdate(entity1);
            session.SaveOrUpdate(entity2);
            session.SaveOrUpdate(entity3 );
            session.Flush();
        }

Why do you need dictionary? Can you change the schema to common one-to-many or many-to-many relation? — lavrik, Oct 29 '13 at 08:38
I need a dictionary because that's how i need the data, i'm getting to the point where ill save a simpler graph and init the more complex one, but i want to avoid that. what do you mean by "change the schema to common one-to-many or many-to-many"? — Royi Mindel, Oct 29 '13 at 11:23
I know it can be saved that way, but that Data doesn't belong in the child, that's how the data needs to be, what is the correct mapping to save IDictionary ? - i already changed it to an Entity3 with Entity1,Entity2 as properties, and IList, and init the Dictionary on load, but i much rather save the Dictionary — Royi Mindel, Oct 29 '13 at 13:19
Can you please post the table structure and domain classes that you are trying to map? — Daniel Schilling, Oct 29 '13 at 15:06
I think @lavrik means using a bag instead of a map, but there's no need to shy away from using a map a.k.a. dictionary, especially if that is a better representation of your domain. — Daniel Schilling, Oct 29 '13 at 15:12
@DanielSchilling thank you, that's why i am asking, added some code — Royi Mindel, Oct 29 '13 at 15:13
What version of NHibernate? At least 3.2 if you're using Mapping by Code... — Daniel Schilling, Oct 29 '13 at 17:42
@DanielSchilling, yes i was talking about bag instead of map, but looking at the answer - i see the idea - useful and nice, thank you. — lavrik, Nov 01 '13 at 16:03

Daniel Schilling · Accepted Answer · 2013-10-29T18:07:44.363

NHibernate Collections

Every NHibernate collection (bag, set, map, list, etc.) has a key and something describing the contents of the collection. A couple collection types, list and map, also have something that describes the index of the collection.

key is the foreign key that points back to the entity that owns the collection.

The contents of the collection will be described by one of the following elements:

one-to-many: the contents of the collection are some kind of entity, and the table for that entity is used as the table for the collection. This implies that the other entity probably has a many-to-one relationship back to this one. Whether you actually end up including that relationship in your object model is a different matter.
many-to-many: the contents of the collection are an entity, but an intermediate table is used for the collection so that the collection elements can be reused by other collections.
element: the contents of the collection are some kind of simple value type, like int, string, etc. A table should be specified for the collection since these value types don't have any particular table they normally live in.
composite-element: Similar to element, but here multiple columns are mapped to properties in a component class.

Finally, for the index, your choices are either:

index: the index is a simple value type, like int or string. This is the only type of index available for lists. On a list, these values correspond directly to the list's index values, list[0], list[1], etc., so non-sequential values in this column will result in some null values in the .NET collection. index has been renamed to list-index and map-key for lists and maps respectively. Both the old and new names should work.
index-many-to-many: the index is an entity. index-many-to-many has been renamed to map-key-many-to-many. The old and new names both work.

There may be a few more options available, but these are the most commonly used ones.

Your Dictionary

In your case, Entity3 has a dictionary of Entity2s, indexed by Entity1, and separate tables are used to keep track of Entity2 and this collection. This means we need a map with a map-key-many-to-many (because the index is an entity) and a many-to-many (because the contents are an entity but we're using a separate table). In HBM XML this would look like:

<map name="Dict" table="Dict">
    <key column="Entity3_ID" />
    <map-key-many-to-many class="Entity1" column="Entity1_ID" />
    <many-to-many class="Entity2" column="Entity2_ID" />
</map>

You do this in FluentNHibernate with the AsEntityMap method:

HasManyToMany(x => x.Dict)
    .Table("Dict")
    .ParentKeyColumn("Entity3_ID")
    .AsEntityMap("Entity1_ID", "Entity2_ID");

With mapping by code, I would imagine that something like this...

Map(x => x.Dict,
    c =>
    {
        c.Table("Dict");
        c.Key(k => k.Column("Entity3_ID"));
    },
    i => i.ManyToMany(m => m.Column("Entity1_ID")),
    v => v.ManyToMany(m => m.Column("Entity2_ID")));

... would do the trick.

I haven't tested the above mappings, and this is my first attempt at mapping by code, so let me know whether it works or not.

Trying the MbC one right now as i have switched from FNH already (haven't decided if it was worth it or not) — Royi Mindel, Oct 29 '13 at 17:19
`map-key-many-to-many` is a recently introduced, more specific, synonym for `index-many-to-many`. When you say "It didn't work", what do you mean? — Daniel Schilling, Oct 29 '13 at 18:05
I SaveOrUpdate Entity1 and Entity2 and then Entity3 - in the DB Entity1, Entity2, Entity3 are saved with IDs , but the Dict table is empty (the connection table) — Royi Mindel, Oct 29 '13 at 18:11
Can you post that saving code? It sounds like you're doing it right, but the problem must be in that code if it's not saving anything to the Dict table. — Daniel Schilling, Oct 29 '13 at 18:22
Updated the question, thank you for the interest you are showing :) — Royi Mindel, Oct 29 '13 at 18:29
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/40267/discussion-between-royi-mindel-and-daniel-schilling) — Royi Mindel, Oct 30 '13 at 17:43

NHibernate MappingByCode mapping a IDictionary

1 Answers1

NHibernate Collections

Your Dictionary