By default MikroORM will propagate all changes made to one side of bi-directional relations to the other side, keeping them in sync. This works for all relations, including M:1 and 1:1. As part of the discovery process, all M:1 and 1:1 properties are re-defined as getter/setter.
const author = new Author(...);const book = new Book(...);book.author = author;console.log(author.books.contains(book)); // true
You can disable this behaviour via
Propagation of Collection's add() and remove() operations
When you use one of
Collection.add() method, the item is added to given collection,
and this action is also propagated to its counterpart.
// one to manyconst author = new Author(...);const book = new Book(...);author.books.add(book);console.log(book.author); // author will be set thanks to the propagation
For M:N this works in both ways, either from owning side, or from inverse side.
// many to many works both from owning side and from inverse sideconst book = new Book(...);const tag = new BookTag(...);book.tags.add(tag);console.log(tag.books.contains(book)); // truetag.books.add(book);console.log(book.tags.contains(tag)); // true
Collections on both sides have to be initialized, otherwise propagation won't work.
Although this propagation works also for M:N inverse side, you should always use owning side to manipulate the collection.
Same applies for