Object Models & Schemas - iOS SDK

Realm Database applications model data as objects composed of field-value pairs that each contain one or more supported data types. Realm objects behave like regular Swift or Objective-C objects, but they also include additional features like real-time updating data views and reactive change event handlers.

Objects of the same class share an object schema that defines the fields and relationships of those objects. Every realm has a schema that consists of one or more object schemas describing the different forms of object that can be stored in that realm.

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To learn how to define a Realm object in Swift or Objective-C, see Define a Realm Object Schema - iOS SDK.

You can identify a property as the primary key of your class. Primary keys are subject to the following limitations:

  • You can define only one primary key per object model.
  • Primary key values must be unique across all instances of an object in a realm. Realm Database throws an error if you try to insert a duplicate primary key value.
  • Primary key values are immutable. To change the primary key value of an object, you must delete the original object and insert a new object with a different primary key value.
  • Embedded objects cannot define a a primary key.
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To learn how to define a primary key for your Realm object, see Specify a Primary Key.

You can create an index on a given property of your model. Indexes speed up some queries, but have a negative impact on insert and update operation speed. Indexes also consume additional space on disk to store the actual index information.

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To learn how to add an index to your Realm object, see Index a Property.

Realm Database supports to-one, to-many, and inverse relationships. You can specify a relationship by adding a reference or list of references to the related Realm object as a property of your Realm object.

Inverse relationship properties contain the set of Realm objects that point to that object instance through a to-one or to-many relationship. Inverse relationships automatically update themselves with corresponding backlinks. You can find the same set of Realm objects with a manual query, but the inverse relationship field reduces boilerplate query code and capacity for error.

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To learn how to add relationships to your Realm object, see Declare Relationship Properties.

  • Realm objects are of a type defined as you would any other class.
  • The Realm object's schema defines the fields of the object and which fields are optional, which fields have a default value, and which fields are indexed.
  • You can define to-one, to-many, and inverse relationships in your schema. Inverse relationships automatically form backlinks.
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