Read data

Read an object from the store. We will be using store.select() to retrieve data from the store.

Get object by primaryKey

Select all fields from user where id is 1.

When selecting by primaryKey, you will only receive one object or null.

Try selecting an ID that does not exist.

Selecting an object

When selecting one object from the store, selecting by primaryKey is the faster way to get data.

example-project/index.js

import {posts} from "./data.js";

// Add some data to the store
store.mutate(posts);

const selectedUser = store.select({

  // From the 'user' model
  from: "user",

  // Return all fields
  // try passing ["id", "username"] into fields
  fields: "*",
  
  // Where the ID is 1
  where: {id: 1},
})

console.log(selectedUser);

Run node index.js and you should see this in the terminal.

{ id: 1, username: 'the_overlord', profileImage: 52, posts: [ 8, 7 ] }

Get object by field value

Select all fields from user where username starts with qw.

When selecting by any field that is not the primaryKey, you will receive an array of objects that matched the where clause.

Where clause

The where clause accepts an object, an array of objects or a function.

example-project/index.js

import {posts} from "./data.js";

// Add some data to the store
store.mutate(posts);

const selectedUser = store.select({
  from: "user",
  fields: "*",
  where: {username: "qwerty"},
  // where: o => o.username.startsWith("qw"),
})

console.log(selectedUser);

Run node index.js and you should see this in the terminal.

[
  { id: 2, username: 'qwerty', profileImage: 48, posts: [ 10, 9, 6 ] }
]

Get many objects

Select all fields from user where id in 1,2.

You can get many objects by primaryKey by passing an array of objects into the where clause

Here's a tip

When a where clause contains a primaryKey field, all other fields are ignored and the data is selected by primaryKey. where: [{id: 1}, {id: 2, username: "Some non existent name"}]

In this where clause, you will still get user 1 and 2.

example-project/index.js

import {posts} from "./data.js";

// Add some data to the store
store.mutate(posts);

const selectedUser = store.select({
  from: "user",
  fields: "*",
  where: [{id: 1}, {id: 2}],
  // where: o => [1,2].includes(o.id),
})

console.log(selectedUser);

Run node index.js and you should see this in the terminal.

[
  {
    id: 1,
    username: 'the_overlord',
    profileImage: 52,
    posts: [ 8, 7 ]
  },
  { id: 2, username: 'qwerty', profileImage: 48, posts: [ 10, 9, 6 ] }
]

Try running the code below as well.

example-project/index.js

import {posts} from "./data.js";

// Add some data to the store
store.mutate(posts);

const selectedUser1 = store.select({
  from: "user",
  fields: "*",
  where: [{id: 1}, {username: "qwerty"}]
})

const selectedUser2 = store.select({
  from: "user",
  fields: "*",
  where: [{id: 1}, o => o.username === "qwerty"]
})

console.log(selectedUser1);
console.log(selectedUser2);

Join objects

In the examples above, you would have noticed that the field value for profileImage was a primaryKey and the value for posts was an array of primaryKey.

Here we will join those objects.

Join

The join will not work if you do not select that field. In this example, we are selecting all fields *,

example-project/index.js

import {posts} from "./data.js";

// Add some data to the store
store.mutate(posts);

const selectedUser = store.select({
  from: "user",

  // Try selecting only ["id", "profileImage"]
  fields: "*",
  where: {id: 1},
  join: [
    {
      on: "profileImage",
      fields: "*",
      join: [
        {on: "thumbnails", fields: "*"}
      ]
    },
    {on: "posts", fields: "*"}
  ]
})

console.log(selectedUser);

Run node index.js and you should see this in the terminal.

{
  id: 1,
  username: 'the_overlord',
  profileImage: { id: 52, aspectRatio: 1.38378, thumbnails: [ [Object], [Object] ] },
  posts: [
    {
      id: 8,
      caption: 'This is post 8',
      createdAt: '2023-06-21T16:13:41.000Z',
      images: [Array],
      user: 1
    },
    {
      id: 7,
      caption: 'This is post 7',
      createdAt: '2023-06-21T13:48:10.000Z',
      images: [Array],
      user: 1
    }
  ]
}

Memonization

Results are memonized

example-project/index.js

import {posts} from "./data.js";

// Add some data to the store
store.mutate(posts);

const a = store.select({ from: "user", fields: ["id"], where: {id: 1} })

const b = store.select({ from: "user", fields: ["id"], where: {id: 1} })

const c = store.select({ from: "user", fields: ["id"], where: o => o.id === 1 })

const d = store.select({ from: "user", fields: ["id"], where: o => o.id === 1 })

const e = store.select({ from: "user", fields: ["id"], where: o => o.id === 2 })

// A and B are the same
console.log(a === b);

// A and C are NOT the same
console.log(a === c);

// C and D are the same
console.log(c === d);

// C and E are NOT the same
console.log(c === e);