EF add data to the same navigation property many to many .

Sachin Singh

6y835Learn iOS Programming

I have a post table and a tag table and bridge table PostTag.

Post 1 has 23 tags , meaning

post p= context.posts.where(p=>p.id=12);

p.tags.Count() =12;

Ok ,fine.

Now I added some new tags to tag table but i want to attach these tags to the same old post

so what i did,

Post p= context.posts.where(p=.p.id=12);
foreach(tag t in tags)
{
p.tags.add(t);
}
context.savechanges();

There is no error, but no output aswell , meaning still post has old tags and new tags are not added to the post.

9 Replies

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Varun Setia6y ago
Congratulations :)
+2
Sachin Singh6y ago
Finally found the solution

Just add new tags to old post as usual like
post.tags=tags //new list of tag
update the post
context.Entry(obj).State = EntityState.Modified;
context.SaveChanges() ;
+3
Varun Setia6y ago
If this code is able to add data correctly including tags, and this post.tags.ToList() is not showing tags then you show data through tagsToUpdate variable
+2
Sachin Singh6y ago
@varun , with your solution tags are added to the database but not getting attach with post.
meaning , post.tags.ToList() // no change.
+2
Varun Setia6y ago
Ok, that's what i was able to conclude first get all the records and include the linked table of tags
var postToUpdate = context.posts.Include("tags").Where(p => p.id==12)
This will obtain the post will all the tags related to it. Now,
List tagsToAdd=new List();
Tag tag=new Tag();
tag.name="great Tag";
tagsToAdd.add(tag);
Now, add data to context
var tagsToUpdate = postToUpdate.tags.ToList();
tagsToUpdate.AddRange(tagsToAdd);

postToUpdate.tags.Clear();
postToUpdate.tags = tagsToUpdate;
context.SaveChanges();
+2
Sachin Singh6y ago
@varun its simple ,
Post table tag table PostTag (postId,TagId)

so , when i added a new post
post.title="a fantastic title";
-----
List tags=new List();
Tag tag=new Tag();
tag.name="great Tag";
tags.add(tag);
post.tags=tags;
context.posts.add(post);
context.savechanges();
here everything is fine post gets added to the post table,tags gets added to the tag table and navigation did its great job;
now i can check all the tags related to that post
that is , Post.Tags.toList();

But the problem is i forgot to add some more tag while adding the post.
Now deleting the post and again adding the post just to add new tags to it is obviously not feasible.
Now tell me whats the solution????
+2
Varun Setia6y ago
Oh! My Mistake. Can you share the entity structure for Post, PostTag and Tag.
+2
Sachin Singh6y ago
@varun ,you din't get my question again
its not about how to load related data(navigation property) rather how to add data to the existing table in many to many condition.
+1
Varun Setia6y ago
Hi,

Try adding navigation property using
Post p= context.posts.Include(p => p.tags).where(p=>p.id=12);
0