Customize primary keys

Customize primary keys

By default, DataStore models have an id field that is automatically populated on the client with a UUID v4, allowing DataStore to generate non-colliding globally unique identifiers in a scalable way. While UUIDs have desirable properties (they are large, non-sequential and opaque), there are times when a custom primary key, also known as custom identifier, is needed. For instance, to:

• Have friendly/readable identifiers (surrogate/opaque vs. natural keys)
• Define composite primary keys
• Customize data partitioning to optimize for scale (especially important when planning to handle large amounts of data in short periods of time)
• Selectively synchronize data to clients (e.g. by fields like deviceId, userId or similar)
• Prioritize the sort order in which objects are returned by the sync queries
• Make existing data consumable and syncable by DataStore

A schema with the typical id field looks like this:

1type Book @model {
2  id: ID!
3  title: String!
4  description: String
5}

You can customize the primary key by adding the @primaryKey directive to a field:

1type Book @model {
2  isbn: ID! @primaryKey
3  title: String!
4  description: String
5}

You can also require multiple fields to define your primary key. When your primary key references multiple fields, it's called a composite key. In the example below, the primary key is defined by the isbn and title fields:

1type Book @model {
2  isbn: ID! @primaryKey(sortKeyFields: ["title"])
3  title: String!
4  description: String
5}

Determine when the primary key field is auto-populated upon record creation

When you create a record with DataStore, a UUID is automatically populated for the default id: ID! primary key field. When working with custom primary keys, DataStore will automatically populate the key fields in the following conditions:

1type Customer @model {
2  firstName: String
3  lastName: String
4}

1type Customer @model {
2  id: ID!
3  firstName: String
4  lastName: String
5}

1type Customer @model {
2  customerId: ID! @primaryKey
3  firstName: String
4  lastName: String
5}

1type Customer @model {
2  id: ID! @primaryKey
3  dob: AWSDateTime!
4  firstName: String
5  lastName: String
6}

1type Customer @model {
2  id: ID! @primaryKey(sortKeyFields: ["dob"])
3  dob: AWSDateTime!
4  firstName: String
5  lastName: String
6}

1type Customer @model {
2  country: String! @primaryKey(sortKeyFields: ["id"])
3  id: ID!
4  firstName: String
5  lastName: String
6}

1type Customer @model {
2  zip: String! @primaryKey(sortKeyFields: ["username"])
3  username: String!
4  firstName: String
5  lastName: String
6}

Querying records with custom primary keys

A record of a model with custom primary key can be queried with query predicate in the following ways:

1final book = (
2  await Amplify.DataStore.query(
3    Book.classType,
4    where: Book.ISBN.eq('12345'),
5  ),
6)[0];

1final book = (
2  await Amplify.DataStore.query(
3    Book.classType,
4    where: Book.MODEL_IDENTIFIER.eq(
5      // BookModelIdentifier is a codegen generated class
6      // that is exported from ModelProvider.dart
7      BookModelIdentifier(
8        isbn: '12345',
9      ),
10    ),
11  ),
12)[0];

1final reQueriedBook = (
2  await Amplify.DataStore.query(
3    Book.classType,
4    where: Book.MODEL_IDENTIFIER.eq(
5      book.modelIdentifier,
6    ),
7  ),
8)[0];