C#•3y ago

EF 6 - Creating entity with n-n

    PostDtoWrite_2 newpost = new PostDtoWrite_2();
    newpost.Title = request.Title;
    newpost.PostDescription = request.PostDescription;
    newpost.LanguageId = request.LanguageId;
    newpost.AccountId = request.AccountId;
    newpost.PostTypeId = request.PostTypeId;
    newpost.CoverImage = request.CoverImage;
    newpost.PublishDate = DateTime.Now;
    newpost.UpdateDate = DateTime.Now;
    newpost.DeletedStatusId = 1;
    newpost.PostTypeId = 1;
    newpost.IsPublished = true;

    try{
        db.Posts.Add(mapper.Map<Post>(newpost));
        await db.SaveChangesAsync();
    } catch (Exception) {
        return Results.StatusCode(580);
    }

    return Results.Ok();

    PostDtoWrite_2 newpost = new PostDtoWrite_2();
    newpost.Title = request.Title;
    newpost.PostDescription = request.PostDescription;
    newpost.LanguageId = request.LanguageId;
    newpost.AccountId = request.AccountId;
    newpost.PostTypeId = request.PostTypeId;
    newpost.CoverImage = request.CoverImage;
    newpost.PublishDate = DateTime.Now;
    newpost.UpdateDate = DateTime.Now;
    newpost.DeletedStatusId = 1;
    newpost.PostTypeId = 1;
    newpost.IsPublished = true;

    try{
        db.Posts.Add(mapper.Map<Post>(newpost));
        await db.SaveChangesAsync();
    } catch (Exception) {
        return Results.StatusCode(580);
    }

    return Results.Ok();

I want to add "Tags" to this but there is no table for many to many in new versions of EF.

48 Replies

İrşatOP•3y ago

public virtual ICollection<Tag> Tags { get; set; } I have this in my entity.

Angius•3y ago

Collection of A in B, collection of B in A All that's needed And get rid of any and all virtual in your models

İrşatOP•3y ago

that's database first, i will delete the virtuals in dtos if there is one but i didn't understand a and b thing

Angius•3y ago

Example model names

İrşatOP•3y ago

let me process it for a minute 😄

Brainiac V•3y ago

First result on Google:

The second most common type of relationship is known as a Many To Many relationship. The following diagram shows how this appears in a database diagram. Each book can belong to many categories and each category can contain many books. This type of relationship is managed in a database through the use of a join table (also known among other things as a bridging, junction or linking table). This type of relationship is defined in code by the inclusion of collection properties in each of the entities:

public class Book
{
    public int BookId { get; set; }
    public string Title { get; set; }
    public Author Author { get; set; }
    public ICollection<Category> Categories { get; set; }
} 
public class Category
{
    public int CategoryId { get; set; }
    public string CategoryName { get; set; }
    public ICollection<Book> Books { get; set; }
}

public class Book
{
    public int BookId { get; set; }
    public string Title { get; set; }
    public Author Author { get; set; }
    public ICollection<Category> Categories { get; set; }
} 
public class Category
{
    public int CategoryId { get; set; }
    public string CategoryName { get; set; }
    public ICollection<Book> Books { get; set; }
}

İrşatOP•3y ago

yeah i already knew that though. But how do I add the Tags, I tried filling this collection but it gave an error also i use mapper, maybe there is something about it too

Angius•3y ago

book.Categories.Add(category);
await _ctx.SaveChangesAsync();

book.Categories.Add(category);
await _ctx.SaveChangesAsync();

İrşatOP•3y ago

Angius•3y ago

You need the actual model intances too, not mapped DTOs

İrşatOP•3y ago

but i am using dto, is there an other way

Angius•3y ago

İrşatOP•3y ago

let me try this first thanks btw

Brainiac V•3y ago

You can see the flow like this: 1) Request comes from the client to get data: Model -> DTO 2) Client sends data that results in creating or updating something: DTO -> Model

İrşatOP•3y ago

2) yes i am using mapper for that db.Posts.Add(mapper.Map<Post>(newpost)); db.Posts.Tags Doesn't exists i guess

Angius•3y ago

You don't have N-N set up, then

İrşatOP•3y ago

public virtual ICollection<Tag> Tags { get; set; } it's there

Angius•3y ago

Ah You need a specific post Not all the posts

İrşatOP•3y ago

i get the tags, i just can't create them in n n table

Angius•3y ago

Of course a DbSet of Posts won't contain a property Tags

var post = await _ctx.Posts.FindAsync(id);
post.Tags.Add(new Tag { ... });
await _ctx.SaveChangesAsync();

var post = await _ctx.Posts.FindAsync(id);
post.Tags.Add(new Tag { ... });
await _ctx.SaveChangesAsync();

İrşatOP•3y ago

so i was thinking i could get the newly created post's id and then add the tags into the n n table. But simply there is no table in ef core 6 😄 let me check what you wrote

Angius•3y ago

You can add it to the newly-created post tho..?

İrşatOP•3y ago

I have Post table, Tags table and Post_Tag table. post.Tags.Add(new Tag { ... }); I don't think that would work

Angius•3y ago

var post = new Post();
post.Tags = new List<Tag>(){
    tag1, tag2, tag3
};
_ctx.Posts.Add(post);
await _ctx.SaveChangesAsync();

var post = new Post();
post.Tags = new List<Tag>(){
    tag1, tag2, tag3
};
_ctx.Posts.Add(post);
await _ctx.SaveChangesAsync();

İrşatOP•3y ago

unless the "tags" here is the n n table here? oh i see but i tried this and got an error

Angius•3y ago

Nothing here is the join table

Brainiac V•3y ago

I think you need to get away from that thinking in relations in databases for a moment

Angius•3y ago

There's zero join tables C#-side

Brainiac V•3y ago

and switch to classes and objects

İrşatOP•3y ago

okay okay i just saw that part. I am just saying i tried this filling the property thing. Catch was triggered, but let me check the error first should i create ICollection or List? as property

Angius•3y ago

List You cannot instantiate interfaces Ah, property? ICollection, List, either's fine

İrşatOP•3y ago

alright is giving id only fine? Tags has an id and body.

Angius•3y ago

Ideally, you'd fetch the tags by ID from the database, but you can use an instance of Tag with ID alone, I think

İrşatOP•3y ago

System.Text.Json.JsonException: A possible object cycle was detected. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 64.

Angius•3y ago

Ah, don't return database models from your API

İrşatOP•3y ago

public List<TagDtoWrite_1>? Tags { get; set; } i am not returning it 😄

Angius•3y ago

Maybe because of the virtual? It enables lazy loading Dunno

İrşatOP•3y ago

this error is completely irrelevant lol

Angius•3y ago

There's a cycle somewhere in what you return

İrşatOP•3y ago

oh maybe it was a different error, i saw it in the terminal. It says this; Cannot insert explicit value for identity column in table 'Tag' when IDENTITY_INSERT is set to OFF. i am not trying to create a tag am i 😄

Angius•3y ago

Ah, when you're adding tags to the post, you do it with new Tag { Id = id } EF takes it as an attempt at creating a tag

İrşatOP•3y ago

i used swagger for that "tags": [ { "id": 1 }, { "id": 2 }, { "id": 3 } ]

Angius•3y ago

So you either have to track those tags, to tell EF those are shims for existing ones, or you have to fetch the tags from the db

var tags = await _ctx.Tags
  .Where(t => tagIds.Contains(t.Id))
  .ToListAsync();

var post = new Post();
post.Tags = tags;

await _ctx.SaveChangesAsync();

var tags = await _ctx.Tags
  .Where(t => tagIds.Contains(t.Id))
  .ToListAsync();

var post = new Post();
post.Tags = tags;

await _ctx.SaveChangesAsync();

This would be the safest way Or... you can create an entity that represents the join table and configure it But I hear you use DB-first, so no clue how to do that I refuse to touch DB-first with a ten-foot pole

İrşatOP•3y ago

it's so fun so far, why tho code first sounds messy

Angius•3y ago

It's the opposite, in my experience You write the code how you want it, define all the relationships as you need them, and never worry about the database At any and all times you work with C# There's no virtuals being generated, no BeanDto_5367s

İrşatOP•3y ago

i see, maybe i learn code first when this is over

foreach (var t in request.Tags)
    {
        newpost.Tags.Add(t);
    }

This add method gives null error. Maybe I can't get the Tags from swagger at all 😄 I will return in 5 minutes

Angius•3y ago

Need to intialize the tags collection Or you can just do newpost.Tags = request.Tags

İrşatOP•3y ago

yup it was already like that, i tried your way to see if there will be a difference and I noticed the null error while it's nullable, foreach gave an error like that welp, i can return the data and it gives me all the tags. I don't know why it says it's null @Angius I remembered your advice about creating an entity instead of the dto. I don't know why I insisted about creating dto and mapping it. I am already getting the data as dto so there is no security risk or anything 😄 It worked, thanks.

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EF 6 - Creating entity with n-n

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