如何在EF Core中添加父记录及其子记录 [英] How to add a parent record with its children records in EF Core
问题描述
下面的示例1曾经可以工作，但是在EF Core中不起作用.问题:如何使下面的示例2正常工作?
Example 1 below used to work but it is not working in EF Core. Question: How to make example 2 below work?
示例1 :
child c1 = new child();
child c2 = new child();
parent p=new parent();
p.child.Add(c1);
p.child.Add(c2);
using (var db = new DbContext())
{
db.parent.Add(p);
db.SaveChanges();
}
实体父P具有一对一关系的子C1和C2.尝试插入父项及其子项记录.但是在以下代码中， VS2017 的编辑器的 intellisense 在行 cust.child.Add(c1)处无法识别.也许，EF Core在插入父/子记录方面有更好的选择.我正在使用ASP.NET .child .; MVC Core 1.1.1 和EF Core 1.1.1
Entity Parent P has children C1, and C2 in a one-to-one relationship. Trying to insert a parent and its children records. But in the following code VS2017's editor's intellisense does not recognize .child at the line cust.child.Add(c1);. Maybe, EF Core has something better for inserting parent/child records. I'm using ASP.NET MVC Core 1.1.1 and EF Core 1.1.1.
示例2 :
...
Parent p = new Parent { Name = "some name" , FY = SelectedYear, ... };
Child c1 = new Child { ItemName = "Abc"};
Child c2 = new Child { ItemName = "Rst"};
p.child.Add(c1);
p..child.Add(c2);
_context.Add(p);
_context.SaveChanges();
更新:
根据来自 @GlennSills 的请求，以下是著名的Blogging Db的示例(摘自
Per a request from @GlennSills, following is an example of well known Blogging Db (taken from this ASP.NET tutorial):
public class BloggingContext : DbContext
{
public BloggingContext(DbContextOptions<BloggingContext> options)
: base(options)
{ }
public DbSet<Blog> Blogs { get; set; }
public DbSet<Post> Posts { get; set; }
}
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
public List<Post> Posts { get; set; }
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogId { get; set; }
public Blog Blog { get; set; }
}
在下面的 Create(...)方法中，在 blog.Posts.Add(c); 行中，我得到了错误: Object reference not设置为对象的实例.
In the Create(...) method below, at line blog.Posts.Add(c); I get the error: Object reference not set to an instance of an object.
public class BlogsController : Controller
{
private readonly BloggingContext _context;
public BlogsController(BloggingContext context)
{
_context = context;
}
....
....
// POST: Blogs/Create
// To protect from overposting attacks, please enable the specific properties you want to bind to, for
// more details see http://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("BlogId,Url")] Blog blog)
{
if (ModelState.IsValid)
{
Post c = new Post();
blog.Posts.Add(c);
_context.Add(blog);
await _context.SaveChangesAsync();
return RedirectToAction("Index");
}
return View(blog);
}
}
推荐答案
将子对象与其父对象一起保存绝对有效.关键是您需要以EF知道所有关系的方式对实体建模.这是一个非常简单的应用程序，您可以看一下. github上的简单应用
Saving child objects along with their parent definitely works. The key is you need to model your entities in such a way that EF knows about all the relationships. Here is a really simple application doing it that you can take a look at. Simple app on github
我有一个看起来像的父母
I have a parent that looks like
using System.Collections.Generic;
namespace EFParentChild
{
public class Parent
{
public int ParentId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public List<Child> Children { get; set; } = new List<Child>();
}
}
这是孩子
namespace EFParentChild
{
public class Child
{
public int Id { get; set; }
public int ParentId { get; set; }
public Parent Parent { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
}
这里是上下文:
使用Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;
namespace EFParentChild
{
class DbParentChild : DbContext
{
public DbSet<Parent> Parents { get; set; }
public DbSet<Child> Children { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=ParentChildDb;Trusted_Connection=True;");
}
}
}
这是保存数据的程序
static void Main(string[] args)
{
using (var dbContext = new DbParentChild())
{
var parent = new Parent
{
FirstName = "Joe",
LastName = "Smith"
};
parent.Children.Add(
new Child
{
FirstName = "LittleJoe",
LastName = "Smith"
});
parent.Children.Add(
new Child
{
FirstName = "Anne",
LastName = "Smith"
});
dbContext.Add(parent);
dbContext.SaveChanges();
}
}
这里的关键是我正在使用约定来告诉EF亲子关系.请注意，两个实体之间使用的ID名称是如何匹配的.子代具有与其父代中的ParentId相匹配的ParentId.还注意到子项中的外键约束.
The key here is that I'm using conventions to tell EF that there is a parent-child relations. Notice how the id names used between the two entities match up. The child has a ParentId that matches ParentId in its parent. Also noticed the foreign key constraint in the child.
我使用实体框架工具创建了表.您可以自己采用这种方法，也可以根据需要手工创建它们.父DDL是:
I created the tables using the entity framework tooling. You can take that approach yourself or create them by hand if you want. The parent DDL is :
CREATE TABLE [dbo].[Parents] (
[ParentId] INT IDENTITY (1, 1) NOT NULL,
[FirstName] NVARCHAR (MAX) NULL,
[LastName] NVARCHAR (MAX) NULL,
CONSTRAINT [PK_Parents] PRIMARY KEY CLUSTERED ([ParentId] ASC)
);
子DDL为:
CREATE TABLE [dbo].[Children] (
[Id] INT IDENTITY (1, 1) NOT NULL,
[FirstName] NVARCHAR (MAX) NULL,
[LastName] NVARCHAR (MAX) NULL,
[ParentId] INT NOT NULL,
CONSTRAINT [PK_Children] PRIMARY KEY CLUSTERED ([Id] ASC),
CONSTRAINT [FK_Children_Parents_ParentId] FOREIGN KEY ([ParentId])
REFERENCES [dbo].[Parents] ([ParentId]) ON DELETE CASCADE
);
GO
CREATE NONCLUSTERED INDEX [IX_Children_ParentId]
ON [dbo].[Children]([ParentId] ASC);
这篇关于如何在EF Core中添加父记录及其子记录的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
