Change an Object Model - Node.js SDK

Schema Version

A schema version identifies the state of a realm schema at some point in time. Realm tracks the schema version of each realm and uses it to map the objects in each realm to the correct schema.

Schema versions are ascending integers that you can optionally include in the realm configuration when you open a realm. If a client application does not specify a version number when it opens a realm then the realm defaults to version 0.

migración

Una migración es una función que actualiza un Realm y cualquier objeto que contenga de una versión de esquema a otra más reciente. Las migraciones te ofrecen la flexibilidad de cambiar tus esquemas de objetos con el tiempo para adaptarte a nuevas funcionalidades y refactorizaciones.

Al abrir un dominio existente con una versión de esquema posterior a la actual, Realm ejecuta una función de migración definida por usted. Esta función tiene acceso al número de versión del dominio y actualiza incrementalmente los objetos para que se ajusten al nuevo esquema.

Realm automatically migrates certain changes, such as new and deleted properties, but does not automatically set values for new properties unless the updated object schema specifies a default value. You can define additional logic in the migration function to further customize property values.

Add a Property

Para agregar una propiedad a un esquema, agregue la nueva propiedad a la clase del objeto y establezca un schemaVersion del objeto de configuración del reino.

const Person = {
  name: 'Person',
  properties: {
    firstName: 'string',
    lastName: 'string',
    age: 'int'
  }
}

const realm = await Realm.open({
    schema: [Person],
    schemaVersion: 2
  });

Eliminar una propiedad

Para eliminar una propiedad de un esquema, elimínela de la clase del objeto y establezca un valor en el objeto schemaVersion de configuración del dominio. Eliminar una propiedad no afecta a los objetos existentes.

const realm = await Realm.open({
    schema: [Dog],
    schemaVersion: 2
  });

Rename a Property

To rename an object property, change the property name in the object schema and then open the realm with an incremented schema version and a migration function that updates existing objects to use the new property name.

Migrations do not allow you to directly rename a property. Instead you can create a new property with the updated name, copy the value from the old property, and then delete the old property.

Realm.open({
  schema: [Person],
  schemaVersion: 2,
  onMigration: (oldRealm, newRealm) => {
    // only apply this change if upgrading to schemaVersion 2
    if (oldRealm.schemaVersion < 2) {
      const oldObjects = oldRealm.objects('Person');
      const newObjects = newRealm.objects('Person');
      // loop through all objects and set the fullName property in the new schema
      for (const objectIndex in oldObjects) {
        const oldObject = oldObjects[objectIndex];
        const newObject = newObjects[objectIndex];
        newObject.fullName = `${oldObject.firstName} ${oldObject.lastName}`;
      }
    }
  }
});

Modify a Property Type

To modify a property's type, set the property type of the field that you wish to modify to the new data type. Then, set a schemaVersion, and a migration callback function of the realm's configuration Object.

const realm = await Realm.open({
    schema: [Dog],
    schemaVersion: 2,
    onMigration: (oldRealm, newRealm) => {
        if(oldRealm.schemaVersion < 2){
            const oldObjects = oldRealm.objects('Dog');
            const newObjects = newRealm.objects('Dog');
            // loop through all objects and set the _id property in the new schema
            for (const objectIndex in oldObjects) {
              const oldObject = oldObjects[objectIndex];
              const newObject = newObjects[objectIndex];
              newObject._id = oldObject._id.toHexString();
            }
        }
    },
  });