我正在尝试使用WPF在Windows 10中重新创建便笺应用程序。 我将实体框架与SQLite数据库一起使用。而且EF无法检索到另一个对象的对象。我该怎么办?
我基本上想在这个数据库中存储2个类 StickyNote和SitckyNoteGroup。每个StickyNote都有一个StickyNoteGroup。 为了让您完全理解,我将发布与问题有关的所有类,但是如果您想使用https://github.com/Kamigoro/StickyNotes,请访问github仓库。
namespace Todo.Models
{
public class StickyNote
{
public int Id { get; set; }
public string Name { get; set; }
public string Text { get; set; }
public StickyNoteGroup Group { get; set; }
public override string ToString()
{
return $"Name : {Name}\nText : {Text}";
}
}
}
namespace Todo.Models
{
public class StickyNoteGroup
{
public int Id { get; set; }
public string Name { get; set; }
public string Color { get; set; }
public override string ToString()
{
return $"Name : {Name}\nColor : {Color}";
}
}
}
我使用EntityFramework的类如下所示,称为NoteContext
using Microsoft.EntityFrameworkCore;
namespace Todo.Models.DataAccess
{
public class NoteContext : DbContext
{
public DbSet<StickyNote> Notes { get; set; }
public DbSet<StickyNoteGroup> NoteGroups { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder options)
=> options.UseSqlite("Data Source=Todo.db");
}
}
最后,我用来执行CRUD操作的类称为DataAccessor,看起来像这样。
namespace Todo.Models.DataAccess
{
public static class DataAccessor
{
public static List<StickyNote> GetStickyNotes()
{
List<StickyNote> notes;
using (var database = new NoteContext())
{
notes = database.Notes.ToList();
}
return notes;
}
public static void SaveStickyNote(StickyNote stickyNote)
{
using (var database = new NoteContext())
{
database.Notes.Add(stickyNote);
database.SaveChanges();
}
}
public static List<StickyNoteGroup> GetStickyNoteGroups()
{
List<StickyNoteGroup> noteGroups;
using (var database = new NoteContext())
{
noteGroups = database.NoteGroups.ToList();
}
return noteGroups;
}
public static void SaveStickyNoteGroup(StickyNoteGroup stickyNoteGroup)
{
using (var database = new NoteContext())
{
database.NoteGroups.Add(stickyNoteGroup);
database.SaveChanges();
}
}
}
}
我的问题是,为什么这部分代码告诉我,即使sqlite数据库中没有当前StickyNote的StickyNoteGroup,也是如此?
private void btnAddStickyNote_Click(object sender, RoutedEventArgs e)
{
StickyNoteGroup group = new StickyNoteGroup() { Name = "Test Group", Color = "Red" };
StickyNote note = new StickyNote() { Name = "Note 1", Text = "An attempt to write a note", Group = group };
DataAccessor.SaveStickyNote(note);
foreach (StickyNote currentNote in DataAccessor.GetStickyNotes())
{
Debug.WriteLine(currentNote.Group.ToString());
}
}
非常感谢您的回答。而且,如果您对我的代码有其他评论,欢迎他们,因为我真的不知道与这样的ORM一起工作的良好模式。
答案 0 :(得分:0)
似乎您需要添加Include
通话:
public static List<StickyNote> GetStickyNotes()
{
List<StickyNote> notes;
using (var database = new NoteContext())
{
notes = database.Notes
.Include(n => n.Group)
.ToList();
}
return notes;
}
顺便说一句,您可以从ToList
语句内部返回经过评估的查询结果数据(例如,通过ToArray
,First
,using
等):
public static List<StickyNote> GetStickyNotes()
{
using (var database = new NoteContext())
{
return database.Notes
.Include(n => n.Group)
.ToList();
}
}