Question

我有一个父班和一个子班。一个孩子总是只与一个父母相关，但是一个父母可以有多个孩子：

public class Parent
{
    public virtual string Id { get; set; }
    public virtual string Name { get; set; }

    public virtual IList<Child> Children { get; set; } = new List<Child>();
}

public class Child
{
    public virtual int Id { get; set; }
    public virtual string ParentId { get; set; }
    public virtual string Name { get; set; }
}

我正在使用最新版本的NHibernate 5.1.3并通过代码进行映射：

internal class ParentMapping : ClassMapping<Parent>
{
    public ParentMapping()
    {
        Table("Parent");

        Id(x => x.Id);
        Property(x => x.Name);

        Bag(
            x => x.Children,
            map =>
            {
                map.Key(km => km.Column("ParentId"));
                map.Lazy(CollectionLazy.NoLazy);
                map.Cascade(Cascade.Persist);
                map.Inverse(true);
            },
            x => x.OneToMany());
    }
}

internal class ChildMapping : ClassMapping<Child>
{
    public ChildMapping()
    {
        Table("Child");

        Id(x => x.Id, x => x.Generator(Generators.Identity));
        Property(x => x.ParentId);
        Property(x => x.Name);
    }
}

查询有效，但是效率很低。无需创建单个JOIN语句来查询子代及其父代，而是进行显式SELECT来检索Child对象。

更糟糕的是，插入结果会导致以下错误：

NHibernate.StaleStateException: 'Batch update returned unexpected row count from update; actual row count: 0; expected: 3'

以下是查询示例：

using (var session = _sessionProvider.GetSession())
    return session.Query<T>().ToList();

这是保存新项目的代码：

using (var session = _sessionProvider.GetSession())
{
    session.Transaction.Begin();
    session.Save(newEntity);
    session.Transaction.Commit();
}

所以一切都很简单。

我认为，ParentMapping中的Bag（）配置需要修复。我在做什么错了？

Answer 1

将bag映射的获取策略更改为join会生成一个join查询，如下所示：

* {
  margin: 0;
  padding: 0;
}

.row {
  background: #f8f9fa;
  margin-top: 20px;
}

.col {
  border: solid 1px #6c757d;
  padding: 10px;
}

body {
  max-width: 960px;
  margin: auto;
}

.cont2 h1 {
  background: black;
  color: lightskyblue;
  padding: 10px;
}

.cont2 nav ul {
  list-style-type: none;
  background: lightskyblue;
  padding: 20px;
}

.cont2 nav ul li {
  display: inline-block;
}

.cont2 nav ul li a {
  text-decoration: none;
  padding: 20px;
  color: black;
  text-transform: uppercase;
}

.cont2 nav ul li a:hover {
  background: black;
  color: orange;
}

.sticky-nav {
  position: sticky;
  box-sizing: border-box;
  top: 0;
  z-index: 1;
}

并且您将集合持久保存为逆（<div class="container cont2"> <h1> Main Heading </h1> <nav class="sticky-nav"> <ul> <li><a href="#"> Page One </a></li> <li><a href="#"> Page Two </a></li> <li><a href="#contact"> Contact </a></li> </ul> </nav> <div class="row"> <div class="col"> <h2> LOREM IPSUM </h2> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> </div> <div class="col"> <h2> LOREM IPSUM </h2> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> </div> </div> <div class="row" id="contact"> <h2> CONTACT ME </h2> <p> Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p> </div> </div>），您应该在Bag( e => e.Children, map => { map.Key(km => km.Column("ParentId")); // map.Lazy(CollectionLazy.NoLazy); // change fetch str map.Fetch(CollectionFetchMode.Join); map.Cascade(Cascade.Persist); map.Inverse(true); }, x => x.OneToMany() );类中为map.Inverse(true);建立多对一映射，如下所示：

Parent

然后将Child属性映射为public class Child { public virtual int Id { get; set; } // public virtual string ParentId { get; set; } public virtual Parent Parent { get; set; } public virtual string Name { get; set; } }，如下所示：

Parent

但是默认情况下，nhibernate不包括父级的子级（可能太重了），如果要查询带有父级实例的子级，可以这样查询：

ManyToOne

要将实体保存到数据库，应执行以下操作：

public ChildMapping() {
    // other mapping goes here
    ManyToOne(
        x => x.Parent,
        map => {
            map.Column("ParentId");
            map.Class(typeof(Parent));
            map.Fetch(FetchKind.Join);
        }
    );
}

NHibernate通过具有OneToMany关联的代码进行映射：选择效率低下，插入失败（NHibernate.StaleStateException）

1 个答案: