在NHibernate中的两个实体之间存在一对多关系:
public class Application
{
public string TaskId { get; set; } // Foreign key reference
public Task Task { get; set; } // The relation/navigation property
}
db.Web.Applications.Create
方法只是在事务中调用NHibernate会话的"SaveOrUpdate"方法。
相关映射:
internal class ApplicationMap : ClassMap<Application>
{
public ApplicationMap() : base()
{
Schema(...);
Table(...);
CompositeId()
.KeyProperty(app => app.UserId, "...")
.KeyProperty(app => app.TaskId, "task_id")
.KeyProperty(app => app.TransactionId, "...");
// Relations
References(app => app.Task, "task_id")
.ForeignKey("taskid")
.Unique()
.Not.Insert()
.Cascade.Persist();
}
}
internal class TaskMap : ClassMap<Task>
{
public TaskMap()
{
Schema(..);
Table(...);
Id(task => task.Id, "task_id");
HasMany(task => task.Applications)
.KeyColumn("task_id");
}
}
当我针对一个真实的数据库编写一个测试来创建一个新的Application
时,我发现导航属性在插入后不会延迟加载:
var app = new Application(...)
{
TaskId = "..."
};
db.Web.Applications.Create(app);
db.SaveChanges();
var actual = db.Web.Applications.Find(app.UserId, app.TaskId, app.TransactionId);
// actual.Task is null
映射按我预期的方式工作,但在插入新的Application
对象后,访问Task
属性将返回null
,而不是从数据库延迟加载该实体。这可以做到吗?如果可以,如何做到?
我认为您的问题来自于映射Application
类及其对应的Task
对象关系的方式。我认为你应该这样映射:
public class Application
{
public Task Task { get; set; } // The relation/navigation property
}
internal class ApplicationMap : ClassMap<Application>
{
public ApplicationMap() : base()
{
Schema(...);
Table(...);
CompositeId()
.KeyProperty(app => app.UserId, "...")
.KeyReference(app => app.Task, "task_id")
.KeyProperty(app => app.TransactionId, "...");
}
}
internal class TaskMap : ClassMap<Task>
{
public TaskMap()
{
Schema(..);
Table(...);
Id(task => task.Id, "task_id");
HasMany(task => task.Applications)
.KeyColumn("task_id");
}
}
没有必要为外键关系映射特定的id属性。我总是只映射实体。这样容易多了。那么你上面要插入的代码是这样的:
var app = new Application(...)
{
Task = session.Load<Task>(taskId)
};
db.Web.Applications.Create(app);
db.SaveChanges();
var actual = db.Web.Applications.Find(app.UserId, app.TaskId, app.TransactionId);