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Model Relationships - Swift SDK
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Declare Relationship Properties
Tip
See also:
Alternatively, you can define your relationships in your App Services app.
Define a To-One Relationship Property
A to-one relationship maps one property to a single instance of another object type. For example, you can model a person having at most one companion dog as a to-one relationship.
Setting a relationship field to null removes the connection between objects. Realm does not delete the referenced object, though, unless it is an embedded object.
Important
To-one relationships must be optional
When you declare a to-one relationship in your object model, it must be an optional property. If you try to make a to-one relationship required, Realm throws an exception at runtime.
Tip
See also:
For more information about to-one relationships, see: To-One Relationship.
If your app uses Device Sync, see the Model Data with Device Sync page for information on how the to-one relationship in Swift object models translates to Atlas documents.
Define a To-Many Relationship Property
A to-many relationship maps one property to zero or more instances of another object type. For example, you can model a person having any number of companion dogs as a to-many relationship.
Tip
See also:
For more information about to-many relationships, see: To-Many Relationship.
If your app uses Device Sync, see the Model Data with Device Sync page for information on how the to-many relationship in Swift object models translates to Atlas documents.
Define an Inverse Relationship Property
An inverse relationship property is an automatic backlink relationship. Realm automatically updates implicit relationships whenever an object is added or removed in a corresponding to-many list or to-one relationship property. You cannot manually set the value of an inverse relationship property.
Tip
See also:
For more information about inverse relationships, see: Inverse Relationship.
If your app uses Device Sync, see the Model Data with Device Sync page for information on how the inverse relationship in Swift object models translates to Atlas documents.
Define an Embedded Object Property
An embedded object exists as nested data inside of a single, specific parent object. It inherits the lifecycle of its parent object and cannot exist as an independent Realm object. Realm automatically deletes embedded objects if their parent object is deleted or when overwritten by a new embedded object instance.
Note
Realm Uses Cascading Deletes for Embedded Objects
When you delete a Realm object, any embedded objects referenced by that object are deleted with it. If you want the referenced objects to persist after the deletion of the parent object, your type should not be an embedded object at all. Use a regular Realm object with a to-one relationship instead.
Tip
See also:
If your app uses Device Sync, see the Model Data with Device Sync page for information on how embedded objects in Swift object models translate to Atlas documents.