[RFC] Rework association methods for better TS support

[ephys]

Is your feature request related to a problem? Please describe.

The way association methods are generated today is cumbersome when using TypeScript.

sequelize-typescript solves this by adding $get, $count, etc methods.

Describe the solution you'd like

I think we could improve developer ergonomics by grouping generated methods in one object.

So instead of looking like this

import {
  Model,
  HasManyGetAssociationsMixin,
  HasManyAddAssociationMixin,
  HasManyHasAssociationMixin,
  HasManyCountAssociationsMixin,
  HasManyCreateAssociationMixin,
  Association,
} from "sequelize";

class User extends Model {
  declare getProjects: HasManyGetAssociationsMixin<Project>; // Note the null assertions!
  declare addProject: HasManyAddAssociationMixin<Project, number>;
  declare addProjects: HasManyAddAssociationsMixin<Project, number>;
  declare setProjects: HasManySetAssociationsMixin<Project, number>;
  declare removeProject: HasManyRemoveAssociationMixin<Project, number>;
  declare removeProjects: HasManyRemoveAssociationsMixin<Project, number>;
  declare hasProject: HasManyHasAssociationMixin<Project, number>;
  declare hasProjects: HasManyHasAssociationsMixin<Project, number>;
  declare countProjects: HasManyCountAssociationsMixin;
  declare createProject: HasManyCreateAssociationMixin<Project, 'ownerId'>;
  declare readonly projects?: Project[];

  declare static associations: {
    projects: Association<User, Project>;
  };
}

The association would look like this:

import { Model, HasManyAttribute } from "sequelize";

class User extends Model {
  declare readonly projects: HasManyAttribute<Project, number>;

  // static associations typings now smart enough, no need to set them :)
}

with HasManyAttribute looking like this

// HasManyAttribute definition (provided by sequelize)
class HasManyAttribute<Model, PrimaryKey> {
  value: Project[] | undefined; // when eager loaded through association. `undefined` when not loaded.
  findOne: HasManyGetAssociationMixin<Model>;
  findAll: HasManyGetAssociationsMixin<Model>;
  add: HasManyAddAssociationMixin<Model, PrimaryKey>;
  bulkAdd: HasManyAddAssociationsMixin<Model, PrimaryKey>;
  setAll: HasManySetAssociationsMixin<Model, PrimaryKey>;
  remove: HasManyRemoveAssociationMixin<Model, PrimaryKey>;
  bulkRemove: HasManyRemoveAssociationsMixin<Model, PrimaryKey>;
  has: HasManyHasAssociationMixin<Model, PrimaryKey>;
  hasMany: HasManyHasAssociationsMixin<Model, PrimaryKey>;
  count: HasManyCountAssociationsMixin;
  create: HasManyCreateAssociationMixin;
}

This would also open the door for a clean decorator support

import { Model, HasManyAttribute, HasMany } from "sequelize";

class User extends Model {
  @HasMany(Project)
  public readonly projects!: HasManyAttribute<Project, number>;
}

Why should this be in Sequelize

I think this way is less verbode, less error prone, and improves typescript users ergonomics.

This solution also enables us to add smart typings for the associations static property. Demo here

Note that this would be a pretty big breaking change.

Describe alternatives/workarounds you've considered

The way sequelize-typescript does it. But this solution lets us use different typings for each association type.

Feature Request Checklist

Is this feature dialect-specific?

• No. This feature is relevant to Sequelize as a whole.

Would you be willing to implement this feature by submitting a Pull Request?

• Yes, I have the time and I know how to start.

[ephys]

Update: After a quick test this would enable having smart typings for the Model.associations static property :)

https://www.typescriptlang.org/play?#code/MYGwhgzhAEAKBOB7AVgU2AFwLKICapGgG8BfAKDNEhgFUJV4d9CizpoIMwMBLYaaomA9uPRADsIALmgAVAKIAPDPDCYAglCEjeEiAB46DJgQB8AbgrsAZj3icAcmAC2qAIQzO8HuIDml9nBHF3dPFR9-Nmgo+FQwXAkQAE9oAAckNEwID2gACUgsMHEk9QxwgCMAVwxUAOhY+MSU1LBY8QwcgCECCV8IWURSiurasnJKIJhNCG1RCSHvKpriKIB9VYwk1NRoAF5oAHJp2d1xBZ4l1APLcaooPIKikrLFkehUZVRxXCmtYTmzi8Lm9WOwAG5gECVULQRDlTIYADaAF1oAAfaCVb6oWziVC4Oq43DqEAgHIACgAlHtTMQSDcJtQHhBCsVjv9TnSKHcYN0QL1+oMgZd3p9vr8ZhyxIDhstQdAIVCYXCEejMdjcfjCT5cBTqbtaaQGYz7nyBQN2TppVyyJttnIlCo1BhLQCDCYQLT9vLEQBpVApHzQADWAcQ1mgHoEMA9foDqI+NXF0Fdp3OIoA-NB-SkZHiwQxkTJYzmE2KfszWc9ZTss-kWU9U9Kouxi3gCHGkmWkxWzX5Bem3lm+30LX8rRIW9A86gC-AbpYyEZGO2QAA6QRSvRr9IodAYCDmaAAemPlcb44BS-oK+YG8vpwgO9aXwwR9P0BHA4fzeXHvvkoTpIa62PYGBOK475nvmDDXsYq4ASc0pPkE4EhFB0AwfAQA

[ephys]

This RFC would also allow us to resolve #7621, as pluralization is used in associations method names

[ephys]

Note from https://gist.github.com/ephys/078ee6a2eb31dc209f0de6cea95316e7:

This would also simplify adding QueryBuilder support:

// non qb version
user.projects.findAll()

// qb version
user.projects.select()
  .orderBy('id', 'ASC')
  .findAll()

[mmahalwy]

This would be amazing! Would be a game-changer to reducing developer mistakes.

[ephys]

Caveat: It's not possible to infer the types of static class fields based on generics.

Model.rawAttributes has been replaced with Model.getAttributes() for this reason.

I think we could deprecate and replace Model.associations with Model.getAssociations(). And also add Model.getAssociation(associationName): Association - which would throw if the association doesn't exist.

[jthoward64]

Is this planned to be held off until v8/beyond or would work on this be accepted?