doc/Database-helpers.md

+Database Helpers
+================
+
+The `DatabaseHelpers<T>` class is a helper to implement some basic functionalities for a dedicated type. It focuses on fetching from the database, but also exposes a helper to delete an entity from the DB.
+
+It is meant to be inherited by the class representing an entity in database. For instance, the `Media` class is declared as such:
+```
+class Media : public IMedia,
+              public DatabaseHelpers<Media>
+```
+
+
+Functionalities
+---------------
+
+* `fetch` allows to fetch a single entity (so a single row from the database). 2 flavors are available: one that uses a primary key, one that takes a request and an arbitrary number of arguments that will be bound to the request
+* `fetchAll` is very similar to fetch, except it will return more than one entity
+* `destroy` will delete an entity with the given primary key from the database 
+* `deleteAll` will delete all entities from the table associated with the entities targeted
+* `insert` is used by the various creation factories to insert the entity in database and fetch the newly inserted entity's primary key
+
+Requirements
+------------
+
+`Table` inner class
+-----------------
+
+All operations need a table name, and must be able to access it based on the `DatabaseHelpers` template parameter. The insertion operation also requires a way to modify the member variable containing the entity primary key.
+
+In order to do so, all classes leveraging the `DatabaseHelpers<T>` class are expected to implement an inner class name `Table`. This class must provide those members:
+* `Name` (`std::string` or compatible) containing the name of the table
+* `PrimaryKeyColumn` (`std::string` or compatible) containing the name of the column holding the primary key
+* `PrimaryKey` (`int64_t T::* const`) storing a pointer to the member containing the primary key
+
+This is enforced through duck typing, but could (and probably should) be expressed through a concept once we can use a recent enough C++ version.
+
+Providing the table name in a dedicated constant also helps finding reference to that table without relying on text based search, which often proves useful.
+
+sqlite::Row based constructor(s)
+--------------------------------
+
+In order for the `fetch` and `fetchAll` helpers to instantiate a class representing a row, all entity classes are expected to expose a constructor taking a media library instance and a database row.
+
+For instance, for the `Media` class again:
+`Media( MediaLibraryPtr ml, sqlite::Row& row );`
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