Update random objects getter

fastapi_book_server/app/services/author.py

@@ -1,6 +1,6 @@
 from app.models import Author
 
-from app.services.common import TRGMSearchService
+from app.services.common import TRGMSearchService, GetRandomService
 
 
 GET_OBJECT_IDS_QUERY = """
@@ -41,3 +41,7 @@ class AuthorTGRMSearchService(TRGMSearchService):
     MODEL_CLASS = Author
     PREFETCH_RELATED = ["source", "annotations"]
     GET_OBJECT_IDS_QUERY = GET_OBJECT_IDS_QUERY
+
+
+class GetRandomAuthorService(GetRandomService):
+    MODEL_CLASS = Author

fastapi_book_server/app/services/book.py

@@ -4,7 +4,7 @@ from fastapi import HTTPException, status
 
 from app.models import Book as BookDB, Author as AuthorDB
 
-from app.services.common import TRGMSearchService
+from app.services.common import TRGMSearchService, GetRandomService
 from app.serializers.book import CreateBook, CreateRemoteBook
 
 
@@ -76,3 +76,7 @@ class BookCreator:
             return await cls._create_book(data)
         if isinstance(data, CreateRemoteBook):
             return await cls._create_remote_book(data)
+
+
+class GetRandomBookService(GetRandomService):
+    MODEL_CLASS = BookDB

fastapi_book_server/app/services/common.py

@@ -122,3 +122,31 @@ class TRGMSearchService(Generic[T]):
             total=total,
             params=params
         )
+
+
+GET_RANDOM_OBJECT_ID_QUERY = """
+SELECT id FROM {table}
+WHERE id >= RANDOM() * (SELECT MAX(id) FROM {table})
+ORDER BY id LIMIT 1;
+"""
+
+
+class GetRandomService(Generic[T]):
+    MODEL_CLASS: Optional[T] = None
+
+    @classmethod
+    @property
+    def model(cls) -> T:
+        assert cls.MODEL_CLASS is not None, f"MODEL in {cls.__name__} don't set!"
+        return cls.MODEL_CLASS
+
+    @classmethod
+    @property
+    def database(cls) -> Database:
+        return cls.model.Meta.database
+
+    @classmethod
+    async def get_random_id(cls) -> int:
+        table_name = cls.model.Meta.tablename
+        query = GET_RANDOM_OBJECT_ID_QUERY.format(table=table_name)
+        return await cls.database.fetch_val(query)

fastapi_book_server/app/services/sequence.py

@@ -1,6 +1,6 @@
 from app.models import Sequence
 
-from app.services.common import TRGMSearchService
+from app.services.common import TRGMSearchService, GetRandomService
 
 
 GET_OBJECT_IDS_QUERY = """
@@ -33,3 +33,7 @@ class SequenceTGRMSearchService(TRGMSearchService):
     MODEL_CLASS = Sequence
     PREFETCH_RELATED = ["source"]
     GET_OBJECT_IDS_QUERY = GET_OBJECT_IDS_QUERY
+
+
+class GetRandomSequenceService(GetRandomService):
+    MODEL_CLASS = Sequence