doc/sqlite/Query.md

@@ -13,7 +13,17 @@ Construction
 
 From the public point of view, the Query objects are read only, and are to be instantiated by the media library itself.
 
+The interface is implemented by 2 possible classes:
+* `SqliteQuery` which implements the main case, and generates a request fetching the results or counting the item depending on which function the user calls
+* `SqliteQueryWithCount` which needs a listing request, and a dedicated count request. This is usefull when the request performs many joins in order to sort the entities, which are not needed when counting.
+
+Choosing between the 2 implementations is up to the developer, there is no dispatching depending on the request.
+
+Both classes can be instantiated using the `make_query` and `make_query_with_count` factories.
+
 Limitations
 ===========
 
-blabla databasehelpers, can't return anything else
+The `IQuery` interface currently enforces the listing function return type to be a `std::vector<std::shared_ptr<T>>`, meaning that there currently isn't a way to return a vector of small trivial object, and a shared_ptr will be instantiated every time.
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+
+The sqlite implementation of those interfaces are assuming that the entity type is a class that inherits the `DatabaseHelpers<T>` helper type, causing it not to be usable for short lived objects or arbitrary requests that do not return a class inheriting `DatabaseHelpers<T>`
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