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Datastore

The Juno Datastore provides a convenient programming model for storing data on the blockchain, eliminating the need to write backend code. This allows for easy management of distributed, cross-user data.

note

To use these features, the Juno SDK must be installed and initialized in your app.

How does it work?

Each satellite you create has a "Datastore", which can have as many collections as you wish.

A collection contains a list of documents, each identified by a textual key that you define.

Each document is a record that holds the data you want to persist on chain, along with timestamps (created and last updated) and an associated owner (the creator of the document).

Timestamps are used to prevent data from being overwritten, and the associated owner is used to grant read and write permissions.

Each document is identified by a key (unique within a collection).

In essence, a "Datastore" functions as a keypair store.

Limitation

Each satellite has specific memory limits. For detailed information, please refer to the related documentation page.

As for documents, they can be up to 2MB in size. However, larger files can be saved in the storage.

Collections

You can create or update a collection in the "Collections" tab in Juno's console under the datastore view.

Rules

A rule is assigned to a collection to define read and write permissions, which can be configured as public, private, managed, or controllers.

  • public: everyone can read from (resp. write to) any document in the collection
  • private: only the owner of a document can read from (resp. write to) a document in the collection
  • managed: the owner of a document and the controllers of the satellite can read from (resp. write to) a document in the collection
  • controllers: only the controllers of the satellite can read from (resp. write to) any document in the collection
tip
  • You can modify the rules at any time, and changes will take effect immediately.
  • Any collection with read permissions set to public, managed or controllers can be viewed by the satellite's controllers in the console under the datastore view.

Memory

When you create a collection, it's assigned to either heap or stable memory. This assignment is permanent and cannot be changed once the collection is created. The default allocation is heap memory.

Add a document

To add a document, use the setDoc function:

import { setDoc } from "@junobuild/core";

await setDoc<Example>({
collection: "my_collection_key",
doc: {
key: "my_document_key",
data: myExample
}
});

You need to provide the collection in which to save the data and the key to use as an index for the document. The data can be any JSON-serializable data.

Key

The key can be any string, but it's recommended to generate IDs using the nanoid library.

import { setDoc } from "@junobuild/core";
import { nanoid } from "nanoid";

const myId = nanoid();

await setDoc<Example>({
collection: "my_collection_key",
doc: {
key: myId,
data: myExample
}
});

Description

A document can be saved with an optional description field, allowing for a maximum length of 1024 characters. This field serves both descriptive purposes and can be used for more granular filtering of your documentation. When retrieving documents, you can also filter based on the description field in addition to the keys, providing additional flexibility and organization options.

import { setDoc } from "@junobuild/core";

await setDoc<Example>({
collection: "my_collection_key",
doc: {
key: "my_document_key_1",
data: myExample,
description: "This is a description"
}
});

await setDoc<Example>({
collection: "my_collection_key",
doc: {
key: "my_document_key_2",
data: myExample,
description: "#programming #technology #web3 #junobuild"
}
});

Get a document

To retrieve data, use the getDoc function and provide the collection and the key of the document:

import { getDoc } from "@junobuild/core";

const myDoc = await getDoc({
collection: "my_collection_key",
key: myId
});

Get multiple documents

Obtaining multiple documents at once can improve performance compared to making multiple individual getDoc calls depending on the use case.

You can achieve this by using the getManyDocs function:

import { getManyDocs } from "@junobuild/core";

const docPair1 = {
collection: "my_collection",
key: "my_document_key_1"
};

const docPair2 = {
collection: "my_other_collection",
key: "my_document_key_2"
};

const docs = await getManyDocs({ docs: [docPair1, docPair2] });

Update a document

To update a document, use the setDoc function with a timestamp to validate that the most recent entry is being updated:

import { setDoc } from "@junobuild/core";

await setDoc<Example>({
collection: "my_collection_key",
doc: {
...myDoc, // includes 'key' and 'updated_at'
data: myNewData
}
});

The updated_at timestamp must match the timestamp of the last document update on the satellite, otherwise the call will fail. This prevents unexpected concurrent updates.

tip

It is common to retrieve the document with getDoc before updating it to ensure that you have the most recent timestamp.

Set multiple documents

You might need to set multiple documents, whether within the same collection or across collections, all at once in an atomic manner. This ensures that if any of the creations or deletions fail, the entire batch will be automatically reverted.

You can achieve this using the setManyDocs function:

import { setManyDocs } from "@junobuild/core";

const update1 = {
collection: "my_collection",
doc: {
key: "my_document_key_1",
data: {
hello: "world"
}
}
};

const update2 = {
collection: "my_other_collection",
doc: {
key: "my_document_key_2",
data: {
count: 123
}
}
};

const docs = await setManyDocs({ docs: [update1, update2] });

List documents

To list documents, use the listDocs function:

import { listDocs } from "@junobuild/core";

const myList = await listDocs({
collection: "my_collection_key"
});

The function accepts various optional parameters, including a matcher (a regex applied to the document keys and descriptions), pagination options, and sorting order.

import { listDocs } from "@junobuild/core";

const myList = await listDocs({
collection: "my_collection_key",
filter: {
order: {
desc: true,
field: "updated_at"
}
}
});

Sorting can be applied descending or ascending to following fields:

  • keys
  • updated_at
  • created_at

Options matcher, paginate and order can be use together.

The function returns various information, in the form of an object whose interface is given below.

{
items: []; // The data - array of documents
items_length: bigint; // The number of documents - basically items.length
items_page?: bigint; // If the query is paginated, at what page (starting from 0) do the items find the place
matches_length: bigint; // The total number of matching results
matches_pages?: bigint; // If the query is paginated, the total number (starting from 0) of pages
}

Delete a document

To delete a document, use the deleteDoc function, which also performs timestamp validation to ensure that the most recent document is being deleted:

import { deleteDoc } from "@junobuild/core";

await deleteDoc<Example>({
collection: "my_collection_key",
doc: myDoc
});

Delete multiple documents

To delete multiple documents in an atomic manner, you can use the function deleteManyDocs:

import { deleteManyDocs } from "@junobuild/core";

await deleteManyDocs({ docs: [myDoc1, myDo2, myDoc3] });