Question

I have an object called Market in my C# 4 application:

public class Market : BusinessBase
{
    public Market()
    {
    }

    public virtual int Id { get; set; }
    public virtual string Symbol { get; set; }
    public virtual string Description { get; set; }
}

I have a table called markets in SQL Server:

CREATE TABLE [dbo].[markets](
    [marketId] [int] IDENTITY(1,1) NOT NULL,
    [symbol] [varchar](10) NOT NULL,
    [description] [varchar](30) NOT NULL,
    [version] [int] NOT NULL,
 CONSTRAINT [PK_markets] PRIMARY KEY CLUSTERED 
    ([marketId] ASC)
GO
CREATE UNIQUE NONCLUSTERED INDEX [NIDX_markets_symbol] ON [dbo].[markets] ([symbol] ASC)
GO

My mapping file looks like this:

<class name="MooDB.BusinessLayer.Market" table="markets">
    <id name="Id" column="marketId" type="Int32">
        <generator class="native" />
    </id>           
    <version name="Version" column="version" type="integer" unsaved-value="0" />
    <property name="Symbol" column="symbol" type="string" length="10" />
    <property name="Description" column="description" type="string" length="30" not-null="true" />        
</class>

I can retrieve a market from the database by Id by simply using this method:

public Market GetMarketById(int marketId)
{
    ISession session = GetSession();
    return session.Get<Market>(marketId);
}

I want to do the same thing but pass in the Symbol instead. Symbol is enforced unique in the database and I want to return a Market object. I am trying this code:

public Market GetMarketBySymbol(string symbol)
{
    ISession session = GetSession();
    return session.Get<Market>(symbol);
}

I know this is wrong but is there a way to return one object which maps to one unique row in the database but not retrieve it by PK? I could simply get an <IList>of Market objects and then just return the one using a ‘foreach’ but that feels inelegant to me.

Answer 1

If you are using NH 3+ you can use LINQ:

return session.Query<Market>().SingleOrDefault(w => w.Symbol == symbol);

Or QueryOver:

return session.QueryOver<Market>()
  .Where(w => w.Symbol == symbol).SingleOrDefault();