NHibernate:如何在一对一映射上启用延迟加载

除非关联是强制性的,否则不支持一对一的延迟加载。看见 here

归根结底,为了确定关系的另一端是否存在(N),Hibernate必须转到数据库。既然您已经访问了数据库,那么不妨加载完整的对象。

据我所知,没有一种非黑客方式可以一对一地延迟加载。我希望我是错的,但上次我检查的时候是这样的。

思想是有办法的。它被描述了 here 详情如下:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernateTest" namespace="NHibernateTest">
  <class name="Person" >
    <id name="PersonID" type="Int32">
      <generator class="identity" />
    </id>
    <property name="LastName" type="String" length="50" />
    <property name="FirstName" type="String" length="50" />
    <many-to-one name="Photo" class="PersonPhoto" />
  </class>

  <class name="PersonPhoto">
    <id name="PersonID" type="Int32">
      <generator class="foreign">
        <param name="property">Owner</param>
      </generator>
    </id>
    <property name="Photo" type="BinaryBlob" />
    <one-to-one name="Owner" class="Person" constrained="true" />
  </class>
</hibernate-mapping> 

this ,我发现地图有点不对劲。当我更改多对一映射以指定列名时,如下所示:

多对一name=“Photo”column=“PersonID”class=“PersonPhoto”unique=“true”

读完这里的答案后,我设法使它起作用。 约束=假

两类:

public class Pedido:BaseModel
{
    public virtual BuscaBase Busca { get; set; }
}

public class BuscaBase : BaseModel
    {       
        public virtual Pedido Pedido { get; set; }
    }

public class PedidoMap : ClassMapping<Pedido>
{
    public PedidoMap()
    {
         Id(x => x.Id, x => x.Generator(Generators.Identity));            

         ManyToOne(x => x.Busca, m => 
         { 
             m.Cascade(Cascade.DeleteOrphans);
             m.NotNullable(true); m.Unique(true);
             m.Class(typeof(BuscaBase));
         });    
    }
}

public class BuscaBaseMap : ClassMapping<BuscaBase>
{
    public BuscaBaseMap()
    {            
        Id(x => x.Id, x => x.Generator(Generators.Sequence, g => g.Params(new { sequence = "buscaefetuada_id_seq" })));

        OneToOne(x => x.Pedido, m =>
        {
            m.Lazy(LazyRelation.NoProxy);
            m.Constrained(false);
            m.Cascade(Cascade.None);
            m.Class(typeof(Pedido));
        });            
    }
}

注意:我使用的是一对一映射 m.PropertyReference(typeof(Pedido).GetProperty("Busca")); 但这对延迟加载不起作用。必须使用类指定关系

  public class Person
    {
        public virtual int Id { get; set; }

        public virtual string Name { get; set; }

        public virtual PersonDetails Details { get; set; }

        public class PersonMap : ClassMapping<Person>
        {
            public PersonMap()
            {
                Id(x => x.Id, m =>
                {
                    m.Generator(Generators.Native);
                });

                 
                Property(x => x.Name);

                OneToOne(x => x.Details, m =>
                { 
                    m.Lazy(LazyRelation.NoProxy);
                    m.Cascade(Cascade.Persist); 
                });
            }
        }
    }

    public class PersonDetails
    {
        public virtual int Id { get; set; }

        public virtual string ExtraDetails { get; set; }

        public virtual Person Person { get; set; }

        public class PersonDetailsMap : ClassMapping<PersonDetails>
        {
            public PersonDetailsMap()
            {

                Id(x => x.Id, m =>
                {
                    m.Generator(Generators.Native);
                }); 

                Property(x => x.ExtraDetails);
                
                ManyToOne(x => x.Person, m =>
                {
                    m.Lazy(LazyRelation.NoProxy);
                    m.Unique(true);
                    m.NotNullable(true); 
                });
            }
        }
    }


using var session = NhHelper.OpenSession();

var person1 = new Person();
person1.Name = "A";

var person1Details = new PersonDetails();
person1Details.ExtraDetails = "A details"; 

person1.Details = person1Details;
person1Details.Person = person1;

session.Save(person1);
//because of PersonMapping's Cascade.Persist it is not necessary to manually save person1Details object.
 

using var session = NhHelper.OpenSession();
foreach(var person in session.Query<Person>()) {
  Console.WriteLine(person.Name);  //<-- does not load PersonDetails unless it's property is accessed
}

• NHibernate 5.3.5