server/posts: include thumbnail URLs in relations

API.md

@@ -68,6 +68,7 @@
    - [Tag category](#tag-category)
    - [Tag](#tag)
    - [Post](#post)
+   - [Micro post](#micro-post)
    - [Note](#note)
    - [Comment](#comment)
    - [Snapshot](#snapshot)
@@ -1625,7 +1626,8 @@ One file together with its metadata posted to the site.
 - `<flags>`: various flags such as whether the post is looped, represented as
   array of plain strings.
 - `<tags>`: list of tag names the post is tagged with.
-- `<relations>`: a list of related post IDs. Links to related posts are shown
+- `<relations>`: a list of related posts, serialized as [micro post
+  resources](#micro-post). Links to related posts are shown
   to the user by the web client.
 - `<notes>`: a list of post annotations, serialized as list of [note
   resources](#note).
@@ -1650,6 +1652,11 @@ One file together with its metadata posted to the site.
   earlier versions.
 - `<comment>`: a [comment resource](#comment) for given post.
 
+## Micro post
+**Description**
+
+A [post resource](#post) stripped down to `name` and `thumbnailUrl` fields.
+
 ## Note
 **Description**
 

server/szurubooru/func/posts.py

@@ -90,7 +90,15 @@ def serialize_post(post, authenticated_user, options=None):
                         tag.category.name,
                         tag.names[0].name)
                 )],
-            'relations': lambda: [rel.post_id for rel in post.relations],
+            'relations': lambda: sorted(
+                {
+                    post['id']:
+                        post for post in [
+                            serialize_micro_post(rel) \
+                                for rel in post.related_by + post.relating_to
+                        ]
+                }.values(),
+                key=lambda post: post['id']),
             'user': lambda: users.serialize_micro_user(post.user),
             'score': lambda: post.score,
             'ownScore': lambda: scores.get_score(post, authenticated_user),
@@ -120,6 +128,12 @@ def serialize_post(post, authenticated_user, options=None):
         },
         options)
 
+def serialize_micro_post(post):
+    return serialize_post(
+        post,
+        authenticated_user=None,
+        options=['id', 'thumbnailUrl'])
+
 def get_post_count():
     return db.session.query(sqlalchemy.func.count(db.Post.post_id)).one()[0]