The contenttype app automatically builds a table that assigns each model type an ID
Thus, with the contenttype framework you can access any model type by it’s model ID
Therefore, any instance in an entire app can be accessed by the combination of two things: the model Class’ contenttype ID and the instance’s primary key
This is why for generic relations you need a field to store a foreign key to ContentTypeand a positive integer field for the instance ID’s you’ll be relating to
ContentType is a model that has fields
id
app_label
model
ContentType.objects.get(app_label=<app_label>, model=<model>) where <model> is the no-space, lowercase model name as a string
Since with the two keys you can access any instance in any Django table, this enables generic relations
A generic relation is a foreign key pointing to any generic model
Without generic relations, you must decide what model the foreign key points to initially. With generic relations the foreign key can point to any model
This allows a model to have a foreign key to any model type (e.g. an attachment model pointing to any other model in the database)
declaring a GenericRelation() is a way to access this in reverse from the model the generic relation points to
Generic relations use composite keys, requiring two hits to the database
Thus it is a performance tradeoff, and these should only be used when necessary
