Nhibernate query for items that have a Dictionary Property containing value

Question

I need a way to query in Nhibernate for items that have a Dictionary Property containing value.

Assume:

public class Item
{
     public virtual IDictionary<int, string> DictionaryProperty {get; set;}
}

and mapping:

    public ItemMap()
    {
        HasMany(x => x.DictionaryProperty)
            .Access.ReadOnlyPropertyThroughCamelCaseField(Prefix.Underscore)
            .AsMap<string>(
                index => index.Column("IDNumber").Type<int>(),
                element => element.Column("TextField").Type<string>().Length(666)
                )
            .Cascade.AllDeleteOrphan()
            .Fetch.Join();
    }

I want to query all Items that have a dictionary value of "SomeText". The following example in Linq fails:

session.Query<Item>().Where(r => r.DictionaryProperty.Any(g => g.Value == "SomeText"))

with error

cannot dereference scalar collection element: Value

So is there any way to achieve that in NHibernate? Linq is not an exclusive requirement but its preffered. Not that I'm not interested to query over dictionary keys that can be achieved using .ContainsKey . Φορ this is similar but not the same

score 4 · Accepted Answer · answered Dec 30 '13 at 09:28

Handling IDictionary<TValueType, TValueType> would usually bring more issues than advantages. One way, workaround, is to introduce a new object (I will call it MyWrapper) with properties Key and Value (just an example naming).

This way we have to 1) create new object (MyWrapper), 2) adjust the mapping and that's it. No other changes... so the original stuff (mapping, properties) will work, because we would use different (readonly) property for querying

public class MyWrapper
{
    public virtual int Key { get; set; }
    public virtual string Value { get; set; }
}

The Item now has

public class Item
{
    // keep the existing for Insert/Updae
    public virtual IDictionary<int, string> DictionaryProperty {get; set;}

    // map it
    private IList<MyWrapper> _properties = new List<MyWrapper>();

    // publish it as readonly
    public virtual IEnumerable<MyWrapper> Properties
    {
        get { return new ReadOnlyCollection<MyWrapper>(_properties); }
    }
}

Now we will extend the mapping:

HasMany(x => x.Properties)
    .Access.ReadOnlyPropertyThroughCamelCaseField(Prefix.Underscore)
    .Component(c =>
    {
        c.Map(x => x.Key).Column("IDNumber")
        c.Map(x => x.Value).Column("TextField")
    })
    ...
    ;

And the Query, which will work as expected:

session
    .Query<Item>()
    .Where(r => 
        r.Properties.Any(g => g.Value == "SomeText")
    )

NOTE: From my experience, this workaround should not be workaround. It is preferred way. NHibernate supports lot of features, but working with Objects brings more profit

Thank you so much for this answer, I didnt even think about it. Once I actually use it and confirm it I will confirm answer and try to also award some bounty for it — Mihalis Bagos, Jan 02 '14 at 20:26
If this would work for you, great. Do not give up to use NHibernate, it is amazing tool. Not as easy to learn, but... so powerful once it is "fully under control" ;) — Radim Köhler, Jan 03 '14 at 04:35
After a glorious fight with the beast that is "composite key and also foreign key" I managed to get rid of the dictionary completely and just use the concrete value wrapper, thanks again — Mihalis Bagos, Jan 03 '14 at 19:13

Nhibernate query for items that have a Dictionary Property containing value

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