QueryOver <a>().Where(a =&gt; a.B.Count() &gt; 0) does not work</a>

Question

我运行时遇到异常：Unrecognised method call in epression a.B.Count()：

var query = session.QueryOver<A>()
    .Where(a => a.B.Count() > 0)
    .List();

以下代码有效：

var query1 = session.QueryOver<A>().List();
var query2 = query1.Where(a => a.B.Count() > 0);

有什么想法吗？感谢。

---

修改

这是我的映射。我正在使用NHibernate 3.1.0.4000：

型号：

public class A
{
    public virtual int Id { get; private set; }
    public virtual ICollection<B> Bs { get; set; }
}

public class B
{
    public virtual int Id { get; private set; }
}

映射：

public class AMappings : ClassMap<A>
{
    public AMappings()
    {
        Id(x => x.Id);
        HasMany(x => x.Bs).LazyLoad();
    }
}

public class BMappings : ClassMap<B>
{
    public BMappings()
    {
        Id(x => x.Id);
    }
}

我的其余代码：

class Program
{
    static void Main(string[] args)
    {
        // Create connection string
        string connectionString = new System.Data.SqlClient.SqlConnectionStringBuilder()
                                   {
                                      DataSource = @".\r2",
                                      InitialCatalog = "TestNHibernateMappings",
                                      IntegratedSecurity = true
                                   }.ConnectionString;

        // Create SessionFactory
        ISessionFactory sessionFactory = Fluently.Configure()
        .Database(MsSqlConfiguration
                      .MsSql2008.ConnectionString(connectionString)
                      .ShowSql())
        .Mappings(m => m.FluentMappings
            .Add(typeof(AMappings))
            .Add(typeof(BMappings)))
        .ExposeConfiguration(BuildSchema)
        .BuildConfiguration()
        .BuildSessionFactory();

        // Test
        var session = sessionFactory.OpenSession();

        // This line works OK
        var query1 = session.Query<A>()
            .Where(a => a.Bs.Count() > 0);

        // This line throws exception: Unrecognised method call in epression a.Bs.Count()
        var query2 = session.QueryOver<A>()
            .Where(a => a.Bs.Count() > 0);
    }

    static void BuildSchema(Configuration cfg)
    {
        new SchemaExport(cfg).Create(false, true);
    }
}

Answer 1

QueryOver不是LINQ。

您的第二个代码段有效，因为它检索所有记录并在内存中使用LINQ到对象。

你应该做的是：

session.Query<A>()
       .Where(a => a.B.Count() > 0)
       .ToList();

或更好：

session.Query<A>()
       .Where(a => a.B.Any())
       .ToList();

Query是一种扩展方法，您需要添加using NHibernate.Linq;