Modeling data

Data records must have a normalized structure that's consistent with Orbit's expectations as well as the constraints of a particular application.

Records

Records are represented as lightweight, serializable POJOs (i.e. "Plain old JavaScript objects").

The structure used for records conforms to the JSONAPI specification. Records can have fields that define their identity, attributes, and relationships with other records.

Here's an example record that represents a planet:

{
  type: 'planet',
  id: 'earth',
  attributes: {
    name: 'Earth',
    classification: 'terrestrial',
    atmosphere: true
  },
  relationships: {
    solarSystem: {
      data: { type: 'solarSystem', id: 'theSolarSystem' }
    },
    moons: {
      data: [
        { type: 'moon', id: 'theMoon' }
      ]
    }
  }
}

Identity

Each record's identity is established by a union of the following fields:

• type - a string that identifies a set of records with a shared definition
• id - a string that uniquely identifies a record of a given type

Both fields must be defined in order for a record to be identified uniquely.

Applications can take one of the following approaches to managing identity:

1. Auto-generate IDs, typically as v4 UUIDs, and then use the same IDs locally and remotely.

2. Auto-generate IDs locally and map those IDs to canonical IDs (or "keys") generated remotely.

3. Remotely generate IDs and don't reference records until those IDs have been assigned.

The first two approaches are "optimistic" and allow for offline usage, while the third is "pessimistic" and requires persistent connectivity.

Note: It's possible to mix these approaches for different types of records (i.e. models) within a given application.

Keys

When using locally-generated IDs, Orbit uses "keys" to support mapping between local and remote IDs.

Remote IDs should be kept in a keys object at the root of a record.

For example, the following record has a remoteId key that is assigned by a server:

{
  type: 'planet',
  id: '34677136-c0b7-4015-b9e5-57f6fdd16bd2',
  keys: {
    remoteId: '123456'
  }
}

The remoteId key of 123456 can be mapped to the locally generated id using a KeyMap, which can be shared by any sources that need access to the mapping. When communicating with the server, remoteId might be serialized as id—such a translation should occur within the source that communicates directly with the remote server (e.g. Orbit's standard JSONAPISource).

Attributes

Any properties that define a record's data, with the exception of relationships to other records, should be defined as "attributes".

All attributes should be contained in an attributes object at the root of a record.

Relationships

Relationships between records should be defined in a relationships object at the root of a record.

Relationship linkage is specified in a data object for each relationship.

For to-one relationships, linkage should be expressed as a record identity object in the form { type, id }. The absence of a relationship can be expressed as null.

For to-many relationships, linkage should be expressed as an array of record identities.

Schema

A Schema defines the models allowed in a source, including their keys, attributes, and relationships. Typically, a single schema is shared among all the sources in an application.

Schemas are defined with their initial settings as follows:

import { Schema } from '@orbit/data';

const schema = new Schema({
  models: {
    planet: {
      attributes: {
        name: { type: 'string' },
        classification: { type: 'string' }
      },
      relationships: {
        moons: { type: 'hasMany', model: 'moon', inverse: 'planet' }
      }
    },
    moon: {
      attributes: {
        name: { type: 'string' }
      },
      relationships: {
        planet: { type: 'hasOne', model: 'planet', inverse: 'moons' }
      }
    }
  }
});

Models should be keyed by their singular name, and should be defined as an object that contains attributes, relationships, and/or keys.

Model attributes

Attributes may be defined by their type, such as "string" or "date", which can be used to define their purpose and contents. An attribute's type may also be used to determine how it should be serialized.

Model relationships

Two types of relationships between models are allowed:

• hasOne - for to-one relationships
• hasMany - for to-many relationships

Relationships must define the related model and may optionally define their inverse, which should correspond to the name of a relationship on the related model. Inverse relationships should be defined when relationships must be kept synchronized, so that adding or removing a relationship on the primary model results in a corresponding change on the inverse model.

Here's an example of a schema definition that includes relationships with inverses:

import { Schema } from '@orbit/data';

const schema = new Schema({
  models: {
    planet: {
      relationships: {
        moons: { type: 'hasMany', model: 'moon', inverse: 'planet' }
      }
    },
    moon: {
      relationships: {
        planet: { type: 'hasOne', model: 'planet', inverse: 'moons' }
      }
    }
  }
});

Model keys

When working with remote servers that do not support client-generated IDs, it's necessary to correlate locally generated IDs with remotely generated IDs, or "keys". Like id, keys uniquely identify a record of a particular model type.

Keys currently accept no standard options, so they should be declared with an empty options hash as follows:

const schema = new Schema({
  models: {
    moon: {
      keys: { remoteId: {} }
    },
    planet: {
      keys: { remoteId: {} }
    }
  }
});

Note: Keys can only be of type "string", which is unnecessary to declare.

Note: A key such as remoteId might be serialized as simply id when communicating with a server. However, it's important to distinguish it from the client-generated id used within Orbit, so it requires a unique name.

Record initialization

Schemas support the ability to initialize records via an initializeRecord() method that takes a record (Record) argument. Currently, initializeRecord just assigns an id to a record if the field is undefined. It may be extended to allow per-model defaults to be set as well.

Here's an example that creates a schema and initializes a record:

import { Schema } from '@orbit/schema';

const schema = new Schema({
  models: {
    planet: {
      attributes: {
        name: { type: 'string' }
      }
    }
  }
});

let earth = {
  type: 'planet',
  attributes: {
    name: 'Earth'
  }
};

schema.initializeRecord(earth);

console.log(earth.id); // "4facf3cc-7270-4b5e-aedd-94d777d31c31"

The default implementation of initializeRecord internally calls the schema's generateId() method to generate an id. By default, this invokes Orbit.uuid() to generate a v4 UUID (where Orbit is the default export from @orbit/core).

It's possible to override generateId for a given schema to use a different local ID scheme. Here's a naive example:

let counter = 0;

const schema = new Schema({
  generateId(type) { return counter++; }
});