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Relational models - JavaScript - AWS Amplify Gen 1 Documentation

The @hasOne and @hasMany directives do not support referencing a model which then references the initial model via @hasOne or @hasMany if DataStore is enabled.

DataStore has the capability to handle relationships between Models, such as has one, has many, belongs to. In GraphQL this is done with the @hasOne, @hasMany and @index directives as defined in the GraphQL Transformer documentation.

For the examples below with DataStore let's add a new model to the sample schema:

In order to save connected models, you will create an instance of the model you wish to connect and pass its ID to DataStore.save:

You can query related models in three ways:

• Option 1: use the toArray() function to lazy load related comments

• Option 2: use async iterators to lazy load related comments

• Option 3: use nested query predicates with the Comment model

When you delete a parent object in a one-to-many relationship, the children will also be removed from the DataStore and mutations for this deletion will be synced to cloud. For example, the following operation would remove the Post with id 123 as well as any related comments:

However, in a many-to-many relationship the children are not removed and you must explicitly delete them.

For many-to-many relationships, you can use the @manyToMany directive and specify a relationName. Under the hood, Amplify creates a join table and a one-to-many relationship from both models.

Join table records must be deleted prior to deleting the associated records. For example, for a many-to-many relationship between Posts and Tags, delete the PostTags join record prior to deleting a Post or Tag.

In order to save a many-to-many relationship, create both model instance first and then save them to a new join model instance.

Here we've first created a new Post instance and a new User instance. Then, saved those instances to a new instance of our join model PostEditor.

To query many-to-many relationships, use a nested predicate to filter the target model by the source model's id:

Deleting the join model instance will not delete any source model instances.

Both the Post and the User instances will not be deleted. Only the join model instances containing the link between a Post and a User.

Deleting a source model instance will also delete the join model instances containing the source model instance.

The toBeDeletedUser User instance and all PostEditor instances where user is linked to toBeDeletedUser will be deleted.

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