When using Isar, you're dealing with Collections. A collection can only contain a single type of Dart object. To let Isar know which objects you want to store, you need to annotate your classes with @Collection(). The Isar code generator will take care of the rest. All the collections combined are called the "database schema".

Annotating classes

The Isar generator will find all classes annotated with @Collection().

class Contact {
  int? id;

  String firstName;

  String lastName;

  bool isStarred;
inheritanceControl whether fields of parent classes and mixins will be stored in Isar. Enabled by default.
accessorAllows you to rename the default collection accessor (for example isar.contacts for the Contact collection).


All model classes need to define an id by annotating a property with @Id() that uniquely identifies an object. Only int properties may be used as id. If a class has a field called id, you can omit the @Id() annotation.

class Pet {
  int? id; // field is called id so an @Id() annotation is not required

  String name;

Isar automatically indexes id fields, which allows you to efficiently read and modify objects based on their id.

You can either set ids yourself or request Isar to assign an auto-increment id. If the id field is null, Isar will use an auto-increment id. You can also assign Isar.autoIncrement to the id field to request an auto-increment id.

Supported types

Isar supports the following data types:

  • bool
  • int
  • double
  • DateTime
  • String
  • Uint8List
  • List<bool>
  • List<int>
  • List<double>
  • List<DateTime>
  • List<String>

It is important to understand how nullability works in Isar: Number types do NOT have a dedicated null-representation. Instead a specific value will be used:


bool, String and List have a separate null representation.

This behavior allows for nice performance improvements and it allows you to change the nullability of your fields freely without requiring migration or special code to handle nulls.


Web does not support NaN. This is an IndexedDB limitation.

➡️ Use TypeConverters to store unsupported types like enums: Type Converters

8-byte and 4-byte numbers

int and double have an 8-byte representation in Dart. By default, this is also true for Isar. You can however change numbers to a 4-byte representation to save disk space by annotating number fields with @Size32(). It is your responsibility to make sure that you do not store a number that requires eight byte in a @Size32() field.

Since JavaScript only supports 64-bit floating point numbers @Size32() has no effect on web.


Isar does not store timezone information of your dates. Instead it converts DateTimes to UTC before storing them. Isar returns all dates in local time.

DateTimes are stored with microsecond precision. In browsers, only millisecond precision is supported because of JavaScript limitations.

Ignoring fields

By default, all public fields of a class will be persisted. By annotating a field with @Ignore(), you can exclude it from persistence. Keep in mind that it is not good practice to store information in your Isar objects that is not persisted.

Renaming classes and fields

You have to be careful when you want to rename a class or field. Most of the time the old class or field will just be dropped and recreated. With the @Name() annotation, you can name classes and fields in the database independantly from Dart. The following code will yield the exact same schema as the code above.

class MyContactClass1 {
  int? myObjectId;

  String theFirstName;

  String familyNameOrWhatever;

  bool isStarred;

Schema migration

It is possible to change the schema between releases of your app (for example by adding collections) but it is very important to follow the rules of schema migration.

You are allowed to do the following modifications:

  • Add & remove collections
  • Add & remove fields
  • Change the nullability of a field (e.g. int -> int? or List<String?>? -> List<String>)
  • Add & remove indexes
  • Add & remove links
  • Change between Link<MyCol> and Links<MyCol> (no data will be lost)



If you rename a field or collection that is not annotated with @Name(), the field or collection will be dropped and recreated.

Deleted fields will still remain in the database. You are not allowed to recreate deleted fields with a different type.



  • Changing the type of fields in existing collections (even previously deleted ones)
  • Creating a unique index for a property with duplicate values