NHibernate 3.0: Using named queries in the data access layer

Getting ready

Download the latest release of the Common Service Locator from http://commonservicelocator.codeplex.com, and extract Microsoft.Practices.ServiceLocation.dll to your solution's libs folder.

Complete the previous recipe, Setting up an NHibernate repository.

Following the Fast testing with SQLite in-memory database recipe in the previous article, create a new NHibernate test project named Eg.Core.Data.Impl.Test.

Include the Eg.Core.Data.Impl assembly as an additional mapping assembly in your test project's App.Config with the following xml:

<mapping assembly="Eg.Core.Data.Impl"/>

How to do it...

1. In the Eg.Core.Data project, add a folder for the Queries namespace.
2. Add the following IQuery interfaces:

   public interface IQuery
   {
   }
   public interface IQuery<TResult> : IQuery
   {
   TResult Execute();
   }

   
   

3. Add the following IQueryFactory interface:

   {
   TQuery CreateQuery<TQuery>() where TQuery :IQuery;
   }

   
   

4. Change the IRepository interface to implement the IQueryFactory interface, as shown in the following code:

   public interface IRepository<T>
   : IEnumerable<T>, IQueryFactory
   where T : Entity
   {
   void Add(T item);
   bool Contains(T item);
   int Count { get; }
   bool Remove(T item);
   }

   
   

5. In the Eg.Core.Data.Impl project, change the NHibernateRepository constructor and add the _queryFactory field, as shown in the following code:

   private readonly IQueryFactory _queryFactory;

   
   public NHibernateRepository(ISessionFactory sessionFactory,
   IQueryFactory queryFactory)
   : base(sessionFactory)
   {
   _queryFactory = queryFactory;
   }

6. Add the following method to NHibernateRepository:

   public TQuery CreateQuery<TQuery>() where TQuery : IQuery
   {
   return _queryFactory.CreateQuery<TQuery>();
   }

   
   

7. In the Eg.Core.Data.Impl project, add a folder for the Queries namespace.
8. To the Eg.Core.Data.Impl project, add a reference to Microsoft.Practices.ServiceLocation.dll.
9. To the Queries namespace, add this QueryFactory class:

   public class QueryFactory : IQueryFactory
   {

   
   private readonly IServiceLocator _serviceLocator;
   
   public QueryFactory(IServiceLocator serviceLocator)
   {
   _serviceLocator = serviceLocator;
   }
   
   public TQuery CreateQuery<TQuery>() where TQuery : IQuery
   {
   return _serviceLocator.GetInstance<TQuery>();
   }
   }

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10. Add the following NHibernateQueryBase class:

    public abstract class NHibernateQueryBase<TResult>
    : NHibernateBase, IQuery<TResult>
    {
    protected NHibernateQueryBase(
    ISessionFactory sessionFactory)
    : base(sessionFactory) { }

    
    public abstract TResult Execute();
    }

11. Add an empty INamedQuery interface, as shown in the following code:

    public interface INamedQuery
    {
    string QueryName { get; }
    }

    
    

12. Add a NamedQueryBase class, as shown in the following code:

    public abstract class NamedQueryBase<TResult>
    : NHibernateQueryBase<TResult>, INamedQuery
    {

    
    protected NamedQueryBase(ISessionFactory sessionFactory)
    : base(sessionFactory) { }
    
    public override TResult Execute()
    {
    var nhQuery = GetNamedQuery();
    return Transact(() => Execute(nhQuery));
    }
    
    protected abstract TResult Execute(IQuery query);
    
    protected virtual IQuery GetNamedQuery()
    {
    var nhQuery = session.GetNamedQuery(
    ((INamedQuery) this).QueryName);
    SetParameters(nhQuery);
    return nhQuery;
    }
    
    protected abstract void SetParameters(IQuery nhQuery);
    
    public virtual string QueryName
    {
    get { return GetType().Name; }
    }
    }

13. In Eg.Core.Data.Impl.Test, add a test fixture named QueryTests inherited from NHibernateFixture.
14. Add the following test and three helper methods:

    [Test]

    
    public void NamedQueryCheck()
    {
    var errors = new StringBuilder();
    
    var queryObjectTypes = GetNamedQueryObjectTypes();
    var mappedQueries = GetNamedQueryNames();
    foreach (var queryType in queryObjectTypes)
    {
    var query = GetQuery(queryType);
    
    if (!mappedQueries.Contains(query.QueryName))
    {
    errors.AppendFormat(
    "Query object {0} references non-existent " +
    "named query {1}.",
    queryType, query.QueryName);
    errors.AppendLine();
    }
    }
    
    if (errors.Length != 0)
    Assert.Fail(errors.ToString());
    }
    
    private IEnumerable<Type> GetNamedQueryObjectTypes()
    {
    var namedQueryType = typeof(INamedQuery);
    var queryImplAssembly = typeof(BookWithISBN).Assembly;
    
    var types = from t in queryImplAssembly.GetTypes()
    where namedQueryType.IsAssignableFrom(t)
    && t.IsClass
    && !t.IsAbstract
    select t;
    return types;
    }
    
    private IEnumerable<string> GetNamedQueryNames()
    {
    var nhCfg = NHConfigurator.Configuration;
    
    var mappedQueries = nhCfg.NamedQueries.Keys
    .Union(nhCfg.NamedSQLQueries.Keys);
    return mappedQueries;
    }
    
    private INamedQuery GetQuery(Type queryType)
    {
    return (INamedQuery) Activator
    .CreateInstance(queryType,
    new object[] { SessionFactory });
    }

15. For our example query, in the Queries namespace of Eg.Core.Data, add the following interface:

    public interface IBookWithISBN : IQuery<Book>
    {
    string ISBN { get; set; }
    }

    
    

16. Add the implementation to the Queries namespace of Eg.Core.Data.Impl using the following code:

    public class BookWithISBN :
    NamedQueryBase<Book>, IBookWithISBN
    {
    public BookWithISBN(ISessionFactory sessionFactory)
    : base(sessionFactory) { }

    
    public string ISBN { get; set; }
    
    protected override void SetParameters(
    NHibernate.IQuery nhQuery)
    {
    nhQuery.SetParameter("isbn", ISBN);
    }
    
    protected override Book Execute(NHibernate.IQuery query)
    {
    return query.UniqueResult<Book>();
    }
    }

17. Finally, add the embedded resource mapping, BookWithISBN.hbm.xml, to Eg.Core.Data.Impl with the following xml code:

    <?xml version="1.0" encoding="utf-8" ?>
    <hibernate-mapping >
    <query name="BookWithISBN">
    <![CDATA[
    from Book b where b.ISBN = :isbn
    ]]>
    </query>
    </hibernate-mapping>