将具有联接的模型添加到许多没有导航属性的模型中 [英] Adding a model with join to another model for many to many without navigation property

问题描述

当我具有如下模型设置时，如何插入属于模型Post的模型Tag:

How can I insert a model Tag that belongs to a model Post when I have the models setup like this:

发布

public class Post
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public virtual ICollection<Tag> Tags { get; set; }
    public Post()
    {
       Tags = new List<Tag>();
    }
}

标记

public class Tag
{
    public int Id { get; set; }
    public string Name { get; set; }
}

此问题建议创建一个Post对象，然后将Tags添加到Tags集合中，但我无法使其正常工作: 插入/更新多对多实体框架.我该怎么办?

This question suggests to create a Post object then add Tags to the Tags collection, I couldn't get it working: Insert/Update Many to Many Entity Framework . How do I do it?

我想在数据库中已经将Tag添加到Post，如何使用EF做到这一点.我是EF的新手.

I want to add Tag to Post already in the database, how can I do that with EF. I'm new to EF.

这是我尝试过的方法，如果将其发送到API，它不会插入任何记录，并且我可以看到数据库中不存在的新tag Id = 0，但是我认为会导致外键约束错误，不确定是否需要为标签自动生成ID:

This is what I've tried, if I send this to the API it doesn't insert any records and I can see that the new tag Id = 0 which doesn't exist in the database, but I'd think that'd cause a foreign key constraint error, not sure If I need to do something to auto generate Id for the tag:

{
    Name: "test"
}

API

[ResponseType(typeof(Tag))]
public IHttpActionResult PostTag(Tag tag)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    var post = new Post();
    var tags = new List<Tag>();
    tags.Add(tag);

    post.Tags.Add(tag);
    post.Id = 10;
    db.Entry(post).State = EntityState.Modified;
    db.SaveChanges();

    return CreatedAtRoute("DefaultApi", new { id = tag.Id }, tag);
}

推荐答案

我先获取帖子，然后添加添加，然后保存更改.

I fetch the Post first add then save changes.

[ResponseType(typeof(Tag))]
public IHttpActionResult PostTag(TagDTO tagDTO)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    var post = db.Posts.Find(TagDTO.PostId);
    post.Tags.Add(new Tag() { Name = tagDTO.Name });            
    db.SaveChanges();

    return CreatedAtRoute("DefaultApi", new { id = post.Tags.First().Id }, post);
}

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