问题
How can I insert a model Tag that belongs to a model Post when I have the models setup like this:
Post
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>();
}
}
Tag
public class Tag
{
public int Id { get; set; }
public string Name { get; set; }
}
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?
I want to add Tag to Post already in the database, how can I do that with EF. I'm new to EF.
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);
}
回答1:
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);
}
来源：https://stackoverflow.com/questions/53977359/adding-a-model-with-join-to-another-model-for-many-to-many-without-navigation-pr