Can't see nested elemets in API call

[tenzan]

System Information

• Strapi Version: 4.4.7
• Operating System:
• Database:
• Node Version:
• NPM Version:
• Yarn Version:

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I want to create relations between Post and Tag as follows.

1. Post has many Tags
2. Tags have and belongs to many Posts

I created collection types for Post and Tag.

Made them publicly available (for public user)

I created 1 post with 3 tags.

Now, when I try to see them at http://localhost:1337/api/posts
I don’t see nested elements, i.e. tags…
Am I missing anything ?

And lastly, I was not able to create Many-to-Many relations between Post and Tag with the following error:

[GregorSondermeier]

You need to add the populate parameter to your REST API requests in order for Strapi to populate the relations.

Population for REST API - Strapi Developer Docs

[tenzan]

Thanks! This worked for Posts.
Could you please advise how to create relation wit Posts for Tag.
Currently, I can’t add relation with the error shown in my last screenshot.

[GregorSondermeier]

That’s odd. Can you show your tag’s schema.json?

[tenzan]

Thanks.

In tag’s schema.json, there’s no relation yet, as I was not able to add in Strapi admin due to error.

{
  "kind": "collectionType",
  "collectionName": "tags",
  "info": {
    "singularName": "tag",
    "pluralName": "tags",
    "displayName": "Tag",
    "description": ""
  },
  "options": {
    "draftAndPublish": true
  },
  "pluginOptions": {},
  "attributes": {
    "name": {
      "type": "string",
      "required": true
    }
  }
}

[GregorSondermeier]

Hmm looks fine to me. How about the post’s schema.json? Is there already a tags attribute?

[tenzan]

Post’s schema.json looks fine.

{
  "kind": "collectionType",
  "collectionName": "posts",
  "info": {
    "singularName": "post",
    "pluralName": "posts",
    "displayName": "Post",
    "description": ""
  },
  "options": {
    "draftAndPublish": true
  },
  "pluginOptions": {},
  "attributes": {
    "title": {
      "type": "string",
      "required": true
    },
    "body": {
      "type": "text",
      "required": true
    },
    "tags": {
      "type": "relation",
      "relation": "oneToMany",
      "target": "api::tag.tag"
    }
  }
}

but I don’t see posts as relation against tag, when accessing http://localhost:1337/api/tags?populate[0]=posts

In this case, posts and tags supposed to be in many-to-many relations.
As Post has all 3 tags, in the screenshot below, eash tag should contain 1 post as nested element.

[tenzan]

http://localhost:1337/api/posts?populate[0]=tags looks correct

[GregorSondermeier]

Ah, your Post schema already contains a tags field which is defined as a oneToMany relation to Tag. The attribute names must be unique.

I see two ways you can change this.

1. UI Way

• In the content type builder, remove the existing tags relation field in the post scheme
• save
• Now you’re free to create the many-to-many relation as you intended

2. Manual way

• In your post’s schema.json, change the tags attribute to:

"tags": {
  "type": "relation",
  "relation": "manyToMany",
  "target": "api::tag.tag",
  "mappedBy": "tags"
}

• In your tag’s schema.json, add a posts attribute:

"posts": {
  "type": "relation",
  "relation": "manyToMany",
  "target": "api::post.post",
  "inversedBy": "posts"
}

---

EDIT:
Actually you can just use the content type builder to change the existing oneToMany relation in the Post to a manyToMany relation, lol. After saving, if you check the other side of that relation (Tag), you will find that it has been added by Strapi automatically.

[tenzan]

Thanks a lot!
Yes, I changed the relations in Post from one-to-many to many-to-many.