In a library database, there are two entities: books and authors. An author can write multiple books, but each book usually has only one author. In this case, the relationship between authors and books is many-to-one. Multiple books can be associated with the same author, but each book can have only one author.
ER Diagram:
Field Configuration:
Parameter Description #
Source Collection #
The source collection, which is the collection where the current field resides.
Target Collection #
The target collection, which is the collection to be associated with.
Foreign Key #
The field in the source collection that is used to establish the association between the two collections.
Target Key #
The field in the target collection that is referenced by the foreign key. It must be unique.
ON DELETE #
ON DELETE refers to the rules applied to foreign key references in related child collections when records in the parent collection are deleted. It is an option used when defining a foreign key constraint. Common ON DELETE options include:
- CASCADE: When a record in the parent collection is deleted, all related records in the child collection are automatically deleted.
- SET NULL: When a record in the parent collection is deleted, the foreign key values in the related child collection records are set to NULL.
- RESTRICT: The default option, it prevents the deletion of a parent collection record if there are related records in the child collection.
- NO ACTION: Similar to RESTRICT, it prevents the deletion of a parent collection record if there are related records in the child collection.
