I was reading about ORMs and one of the descriptions I read said that the ORM interacts with database metadata.
Why is this important or relevant?
Metadata, as I understand, is just a way of describing what the database contains. So, for example, the database might have an internal table that lists what user tables have been created. Why would something like this be useful to an ORM?
The ORM uses the metadata to generate the code used to access the tables. For example, if it's a date column then it generates the code to deal with that column as a date.
It will read foreign keys and primary keys to build relationships in the code as well as for generating the proper SQL syntax.
This is just a few of the ways it uses the metadata.
What this means is that the ORM maps the schema, or structure, of the database to objects. Typically, this means mapping tables to classes (User table to User class), fields to attributes (Age field to User.Age attribute), and each record then represents an instance of that object.