Data modeling

Each Parse class is a MongoDB collection; each object, a document. Good models come from the screens you'll build: model for how you read the data, not only for how you store it.

Field types

Type	For
String, Number, Boolean, Date	Plain values
Object, Array	Nested JSON: small, read together with the object
Pointer	A reference to one other object
Relation	A many-to-many link, stored apart from the object
File	An uploaded file
GeoPoint	A location, for "near me" queries
ACL	Who may read and write the object

Define the schema in Core › Browser (or with the API) rather than letting clients create fields, and keep Add field off for clients (Secure your app).

Linking objects

	Pointer	Array of pointers	Relation
Shape	One-to-one, many-to-one	One-to-few	Many-to-many, many-to-lots
Example	A comment's post	A post's 3 tags	A user's followers
Read with the object	include('post'), same request	include('tags')	A separate query
Size	1	Keep it small (tens)	Unbounded

const comment = new Parse.Object('Comment', { text: 'Nice!', post });
await comment.save();

// comments of a post, with the post itself in one request
const comments = await new Parse.Query('Comment')
  .equalTo('post', post)
  .include('post')
  .descending('createdAt')
  .limit(20)
  .find();

Prefer a pointer from the "many" side (the comment points to its post) over an array on the "one" side: it grows without limit, and it queries and indexes well.

Denormalize what you show often

Reading related objects on every screen costs requests. Copy what you need where you read it:

• a commentCount on the post, kept up to date in an afterSave of Comment;
• the author's name next to the author pointer, if lists show it;
• the latest message's text on the conversation.

Copies get stale, so update them in cloud code, not from clients.

Model for permissions

Permissions apply per class and per object, so split data by who may see it:

• public profile fields in a Profile class readable by everyone; email and settings stay in _User, readable only by the user;
• one object per owner, with the owner's ACL, rather than a shared object that everyone updates.

Model for speed

• Query by fields you can index, and sort by them.
• Avoid huge objects: big arrays and nested objects are read and rewritten in full on every save.
• Keep large data (images, documents, exports) in files, not in fields.

Parse's JavaScript guide covers every relation API in detail.