started a documentation

documentation/objects.md

@@ -0,0 +1,36 @@
+# music_kraken.objects
+
+## DatabaseObject
+
+[music_kraken.objects.DatabaseObject](../src/music_kraken/objects/parents.py)
+
+## Collection
+
+[music_kraken.objects.Collection](../src/music_kraken/objects/collection.py)
+
+This is an object, which acts as a list. You can save instaces of a subclass of [DatabaseObject](#databaseobject).
+
+Then you can for example append a new Object. The difference to a normal list is, that if you have two different objects that both represent the same data, it doesn't get added, but all data gets merged into one Object instead.
+
+For example, you have two different Artist-Objects, where both have one source in common. The one Artist-Object already is in the Collection. The other artist object is passed in the append command.  
+In this case it doesn't simply add the artist object to the collection, but modifies the already existing Artist-Object, adding all attributes the new artist object has, and then discards the other object.
+
+```python
+artist_collection = Collection(element_type=Artist)
+
+# adds the artist to the list (len 1)
+artist_collection.append(artist_1)
+
+# detects artist 2 has a mutual source
+# thus not adding but mergin (len 1)
+artist_collection.appent(artist_2)
+```
+
+Function | Explanation
+---|---
+`append()` | appends an object to the collection
+`extend()` | appends a list of objects to the collection
+`__len__()` | gets the ammount of objects in collection
+`shallow_list` | gets a shallow copy of the list `_data` the objects are contained in
+`sort()` | takes the same arguments than `list.sort`, and does the same
+`__iter__()` | allows you to use collections e.g. a for loop