feat(types): add generics types for associations (#10524)

types/lib/associations/base.d.ts

-import { ColumnOptions, Model } from '../model';
+import { ColumnOptions, Model, ModelCtor } from '../model';
 
-export abstract class Association {
+export abstract class Association<S extends Model = Model, T extends Model = Model> {
   public associationType: string;
-  public source: typeof Model;
-  public target: typeof Model;
+  public source: ModelCtor<S>;
+  public target: ModelCtor<T>;
   public isSelfAssociation: boolean;
   public isSingleAssociation: boolean;
   public isMultiAssociation: boolean;

types/lib/associations/belongs-to-many.d.ts

@@ -6,6 +6,7 @@ import {
   InstanceDestroyOptions,
   InstanceUpdateOptions,
   Model,
+  ModelCtor,
   Transactionable,
   WhereOptions,
 } from '../model';
@@ -68,10 +69,10 @@ export interface BelongsToManyOptions extends ManyToManyOptions {
   timestamps?: boolean;
 }
 
-export class BelongsToMany extends Association {
+export class BelongsToMany<S extends Model = Model, T extends Model = Model> extends Association<S, T> {
   public otherKey: string;
   public accessors: MultiAssociationAccessors;
-  constructor(source: typeof Model, target: typeof Model, options: BelongsToManyOptions);
+  constructor(source: ModelCtor<S>, target: ModelCtor<T>, options: BelongsToManyOptions);
 }
 
 /**

types/lib/associations/belongs-to.d.ts

 import { DataType } from '../data-types';
-import { CreateOptions, FindOptions, Model, SaveOptions } from '../model';
+import { CreateOptions, FindOptions, Model, ModelCtor, SaveOptions } from '../model';
 import { Promise } from '../promise';
 import { Association, AssociationOptions, SingleAssociationAccessors } from './base';
 
+// type ModelCtor<M extends Model> = InstanceType<typeof M>;
 /**
  * Options provided when associating models with belongsTo relationship
  *
@@ -21,9 +22,9 @@ export interface BelongsToOptions extends AssociationOptions {
   keyType?: DataType;
 }
 
-export class BelongsTo extends Association {
+export class BelongsTo<S extends Model = Model, T extends Model = Model> extends Association<S, T> {
   public accessors: SingleAssociationAccessors;
-  constructor(source: typeof Model, target: typeof Model, options: BelongsToOptions);
+  constructor(source: ModelCtor<S>, target: ModelCtor<T>, options: BelongsToOptions);
 }
 
 /**

types/lib/associations/has-many.d.ts

@@ -5,6 +5,7 @@ import {
   FindOptions,
   InstanceUpdateOptions,
   Model,
+  ModelCtor,
   Transactionable,
   WhereOptions,
 } from '../model';
@@ -22,9 +23,9 @@ export interface HasManyOptions extends ManyToManyOptions {
   keyType?: DataType;
 }
 
-export class HasMany extends Association {
+export class HasMany<S extends Model = Model, T extends Model = Model> extends Association<S, T> {
   public accessors: MultiAssociationAccessors;
-  constructor(source: typeof Model, target: typeof Model, options: HasManyOptions);
+  constructor(source: ModelCtor<S>, target: ModelCtor<T>, options: HasManyOptions);
 }
 
 /**

types/lib/associations/has-one.d.ts

 import { DataType } from '../data-types';
-import { CreateOptions, FindOptions, Model, SaveOptions } from '../model';
+import { CreateOptions, FindOptions, Model, ModelCtor, SaveOptions } from '../model';
 import { Promise } from '../promise';
 import { Association, AssociationOptions, SingleAssociationAccessors } from './base';
 
@@ -13,9 +13,9 @@ export interface HasOneOptions extends AssociationOptions {
   keyType?: DataType;
 }
 
-export class HasOne extends Association {
+export class HasOne<S extends Model = Model, T extends Model = Model> extends Association<S, T> {
   public accessors: SingleAssociationAccessors;
-  constructor(source: typeof Model, target: typeof Model, options: HasOneOptions);
+  constructor(source: ModelCtor<S>, target: ModelCtor<T>, options: HasOneOptions);
 }
 
 /**

types/lib/model.d.ts

@@ -2192,7 +2192,9 @@ export abstract class Model<T = any, T2 = any> extends Hooks {
    * @param target The model that will be associated with hasOne relationship
    * @param options Options for the association
    */
-  public static hasOne(target: typeof Model, options?: HasOneOptions): HasOne;
+  public static hasOne<M extends Model, T extends Model>(
+    this: ModelCtor<M>, target: ModelCtor<T>, options?: HasOneOptions
+  ): HasOne<M, T>;
 
   /**
    * Creates an association between this (the source) and the provided target. The foreign key is added on the
@@ -2203,8 +2205,10 @@ export abstract class Model<T = any, T2 = any> extends Hooks {
    * @param target The model that will be associated with hasOne relationship
    * @param options Options for the association
    */
-  public static belongsTo(target: typeof Model, options?: BelongsToOptions): BelongsTo;
-
+  public static belongsTo<M extends Model, T extends Model>(
+    this: ModelCtor<M>, target: ModelCtor<T>, options?: BelongsToOptions
+  ): BelongsTo<M, T>;
+    
   /**
    * Create an association that is either 1:m or n:m.
    *
@@ -2257,7 +2261,9 @@ export abstract class Model<T = any, T2 = any> extends Hooks {
    * @param target The model that will be associated with hasOne relationship
    * @param options Options for the association
    */
-  public static hasMany(target: typeof Model, options?: HasManyOptions): HasMany;
+  public static hasMany<M extends Model, T extends Model>(
+    this: ModelCtor<M>, target: ModelCtor<T>, options?: HasManyOptions
+  ): HasMany<M, T>;
 
   /**
    * Create an N:M association with a join table
@@ -2307,7 +2313,9 @@ export abstract class Model<T = any, T2 = any> extends Hooks {
    * @param options Options for the association
    *
    */
-  public static belongsToMany(target: typeof Model, options: BelongsToManyOptions): BelongsToMany;
+  public static belongsToMany<M extends Model, T extends Model>(
+    this: ModelCtor<M>, target: ModelCtor<T>, options: BelongsToManyOptions
+  ): BelongsToMany<M, T>;
 
   /**
    * Returns true if this instance has not yet been persisted to the database
@@ -2511,4 +2519,8 @@ export abstract class Model<T = any, T2 = any> extends Hooks {
   public toJSON(): object;
 }
 
+export type ModelType = typeof Model;
+
+export type ModelCtor<M extends Model> = { new (): M } & ModelType;
+
 export default Model;

types/test/models/User.ts

@@ -6,12 +6,13 @@ import {
   DataTypes,
   FindOptions,
   Model,
+  ModelCtor
 } from 'sequelize';
 import { sequelize } from '../connection';
 
 export class User extends Model {
   public static associations: {
-    group: BelongsTo
+    group: BelongsTo<User, UserGroup>;
   };
 
   public id: number;
@@ -68,7 +69,12 @@ User.afterFind((users, options) => {
 User.addHook('beforeFind', 'test', (options: FindOptions) => {
   return undefined;
 });
+
 // associate
 // it is important to import _after_ the model above is already exported so the circular reference works.
 import { UserGroup } from './UserGroup';
 export const Group = User.belongsTo(UserGroup, { as: 'group', foreignKey: 'groupId' });
+
+// associations refer to their Model
+const userType: ModelCtor<User> = User.associations.group.source;
+const groupType: ModelCtor<UserGroup> = User.associations.group.target;

types/test/models/UserGroup.ts

@@ -16,7 +16,7 @@ import { sequelize } from '../connection';
 
 export class UserGroup extends Model {
     public static associations: {
-        users: HasMany
+        users: HasMany<UserGroup, User>
     };
 
     public id: number;