Managing Local State
At its core, Apollo Client is a state management library that happens to use GraphQL to interact with a remote server. Naturally, some application state doesn’t require a remote server because it’s entirely local.
Apollo Client enables you to manage local state alongside remotely fetched state, meaning you can interact with all of your application’s state with a single API.
How It Works
Please read the “How it works” chapter on Apollo Client documentation.
Field Policies and Local-Only Fields
Field policies enable you to define what happens when you query a particular field, including
fields that aren’t defined in your GraphQL server’s schema. By defining field policies for these
local-only fields, you can populate them with data that’s stored anywhere, such as in
localStorage or reactive variables.
A single GraphQL query can include both local-only fields and remotely fetched fields. In the field policy for each local-only field, you specify a function that defines how that field’s value is populated.
Get started with local-only fields
Reactive Variables
Reactive variables enable you to read and write local data anywhere in your application, without needing to use a GraphQL operation to do so. The field policy of a local-only field can use a reactive variable to populate the field’s current value.
Reactive variables aren’t stored in the Apollo Client cache, so they don’t need to conform to the strict structure of a cached type. You can store anything you want in them.
Whenever the value of a reactive variable changes, Apollo Client automatically detects that change. Every active query with a field that depends on the changed variable automatically updates.
Get started with reactive variables
Local Resolvers
In Apollo Client, you can define local resolvers to populate and modify local-only fields. These resolvers are similar in structure and purpose to the resolvers that your GraphQL server defines.