NullReferenceException mapping collection of enum with Fluent NHibernate automapping

Question

I have a class that contains a collection of enumeration as follows.

public enum TransactionType
{
  ...
}

public class PaymentMethod
{
  ...
  public virtual IList<TransactionType> SupportedTransactionTypes { get; set; }
}

Other references to the TransactionType enumeration are working correctly but with this collection I get an exception: "NHibernate.MappingException : Association references unmapped class: mynamespace.TransactionType".

Looking around it seems like I needed to specify the type of element mapping, i.e. one-to-many, element, or composite-element.

I have setup the following override mappings for the PaymentMethod class:

mapping.HasMany(x => x.TransactionTypes)
  .Element("TransactionTypeId"), x => x.Type<TransactionType>());

But this causes the following exception...

Validation failed: System.NullReferenceException: Object reference not set to an instance of an object. at FluentNHibernate.Conventions.Inspections.OneToManyInspector.get_Class() in e:\horn.horn\orm\fluentnhibernate\Working\src\FluentNHibernate\Conventions\Inspections\OneToManyInspector.cs:line 40 at FluentNHibernate.Conventions.ProxyConvention.Apply(ICollectionInstance instance) in e:\horn.horn\orm\fluentnhibernate\Working\src\FluentNHibernate\Conventions\ProxyConvention.cs:line 79 at FluentNHibernate.Visitors.ConventionVisitor.Apply[TInspector,TInstance](IEnumerable conventions, TInstance instance) in e:\horn.horn\orm\fluentnhibernate\Working\src\FluentNHibernate\Visitors\ConventionVisitor.cs:line 269 at ...

I have tried a lot of different variations on the mapping, including TableName, KeyColumn and anything else I can think of but I can't get this mapping to work.

Any help appreciated...

Answer 1

Perhaps this is a recent fix in FluentNHibernate, but this works with FluentNH v1.2.0.712. I'm fairly confident that NHibernate with plain *.hbm.xml mappings has supported this type of mapping for years.

This is the automapping override that worked for me:

mapping.HasMany(x => x.SupportedTransactionTypes)
    .Element("TransactionTypeId");

...which results in this XML...

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class xmlns="urn:nhibernate-mapping-2.2" name="so.Q2676867.PaymentMethod, so, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="`PaymentMethod`">
    <id access="backfield" name="Id" type="System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <column name="Id" />
      <generator class="identity" />
    </id>
    <bag name="SupportedTransactionTypes">
      <key>
        <column name="PaymentMethod_id" />
      </key>
      <element type="so.Q2676867.TransactionType, so, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
        <column name="TransactionTypeId" />
      </element>
    </bag>
  </class>
</hibernate-mapping>

... and these tables:

create table [PaymentMethod] (
    Id INT IDENTITY NOT NULL,
   primary key (Id)
)

create table SupportedTransactionTypes (
    PaymentMethod_id INT not null,
   TransactionTypeId INT null
)

alter table SupportedTransactionTypes 
    add constraint FK738E3751B597A1C 
    foreign key (PaymentMethod_id) 
    references [PaymentMethod]

... which is exactly what I would expect. Yay NHibernate!

Answer 2

You could persist the collection in the database as a pipe-delimited string...

    protected string _enumCollection = "";    
    public virtual ISet<MyEnum> EnumCollection
    {
        get
        {
            var set = new HashedSet<MyEnum>();

            if (string.IsNullOrEmpty(_enumString))
                return set;

            _enumCollection.Split(new[] {"|"}, StringSplitOptions.None).ToList()
                .ForEach(
                    x => set.Add((MyEnum)(Int32.Parse(x)))
                );
            return new HashedSet<MyEnum>(set);
        }
        set { _enumCollection = string.Join("|", value.Select(x => ((int)x).ToString()).ToArray()); }
    }

and then map to the string backing field:

Map(x => x.EnumCollection).CustomType(typeof(string)).Access.CamelCaseField(Prefix.Underscore);

You'll need to use helper methods to add/remove enums rather than using the methods on the collection itself in order to update the backing field.

public virtual void AddEnum(MyEnum enum)
        {
            if (!EnumCollection.Contains(enum))
            {
                var set = EnumCollection; //you need to get the collection
                set.Add(enum); //add enum to it
                EnumCollection= set; //then set the set again
            }
        }

        public virtual void RemoveEnum(MyEnum enum)
        {
            if (EnumCollection.Contains(enum))
            {
                var set = EnumCollection; //get collection
                set.Remove(enum); //add enum 
                EnumCollection= set; //re-set collection
            }
        }

Hope this helps.

Answer 3

I dont think you can map a collection of enums. You certainly couldnt a year or so ago