Pagination of relations?

[docelic]

Hello,

The docs and tests show pagination on a single Sequelize model. But is it possible to paginate on model associations like author.getBooks()?

(In node's GraphQL implementation of connections it is transparently (for the user, at least) possible to paginate models and associations.)

[docelic]

Hello, Any comments/hints on this question?

[Kaltsoon]

There's no direct support, but quite simple workaround would be to use the Book model with appropriate query:

Book.paginate({
  limit: 20,
  where: {
    authorId: author.id // or whatever the foreign key is
  },
});

And this could be implemented as a method such as getPaginatedBooks() without too much hassle:

class Author {
  // ...
 getPaginatedBooks(options) {
   return Book.paginate({
      ...options,
      where: {
        ...options?.where,
        authorId: this.id,
      },
    });
 }
}

[docelic]

Yes, certainly, although I wanted to avoid that since it means duplicating the relation's query/conditions.

[docelic]

GraphQL's connection fields can be transparently created on either model or relations. Time-permitting I'll see if it is easily identifiable from the code how they did it.

[Kaltsoon]

Yes, certainly, although I wanted to avoid that since it means duplicating the relation's query/conditions.

I don't see this as a major issue. Relation conditions change very rarely and only one method needs to be changed if that happens

[docelic]

A patch as simple as this makes it possible to paginate associations.

diff -ru sequelize-cursor-pagination/makePaginate.js sequelize-cursor-pagination/makePaginate.js
--- sequelize-cursor-pagination/makePaginate.js    2022-08-04 22:50:45.774000000 +0200
+++ sequelize-cursor-pagination/makePaginate.js 2022-08-04 22:45:08.181000000 +0200
@@ -2,10 +2,21 @@
 Object.defineProperty(exports, "__esModule", { value: true });
 const sequelize_1 = require("sequelize");
 const utils_1 = require("./utils");
-const makePaginate = (model, options) => {
+
+function checkIsAssociation(target) {
+  return !!target.associationType;
+}
+
+const makePaginate = (target, options) => {
+    const isAssociation = checkIsAssociation(target)
+    const findFunction = isAssociation ? target.accessors.get : 'findAll'
+    const countFunction = isAssociation ? target.accessors.count : 'count'
+    const model = isAssociation ? target.target : target
+
     const primaryKeyField = options?.primaryKeyField ?? (0, utils_1.getPrimaryKeyFields)(model);
     const omitPrimaryKeyFromOrder = options?.omitPrimaryKeyFromOrder ?? false;
-    const paginate = async (queryOptions) => {
+    const paginate = async (queryOptions, source) => {
+        if (!isAssociation) source = model;
         const { order: orderOption, where, after, before, limit, ...restQueryOptions } = queryOptions;
         const normalizedOrder = (0, utils_1.normalizeOrder)(orderOption, primaryKeyField, omitPrimaryKeyFromOrder);
         const order = before ? (0, utils_1.reverseOrder)(normalizedOrder) : normalizedOrder;
@@ -33,9 +44,9 @@
             ...restQueryOptions,
         };
         const [instances, totalCount, cursorCount] = await Promise.all([
-            model.findAll(paginationQueryOptions),
-            model.count(totalCountQueryOptions),
-            model.count(cursorCountQueryOptions),
+            source[findFunction](paginationQueryOptions),
+            source[countFunction](totalCountQueryOptions),
+            source[countFunction](cursorCountQueryOptions),
         ]);
         if (before) {
             instances.reverse();

Associations require an instance to start querying from, rather than just a model. Sequelize keeps track of model's associations in Model.associations hash, along with all necessary data. Knowing that, and assuming we have Author -> Books relation defined in Sequelize, the usage would be:

paginatedBooksFromAuthor = await makePaginate(Author.associations.books)
author = await Author.findOne()
await paginatedBooksFromAuthor( {order: 'id'}, author )

This is just an in-place patch for .js as a proof of concept showing that it works. Let me know if you'd be willing to merge if a proper PR was made.

[Kaltsoon]

Seems like a quite clean solution. If you can turn this into a PR it would be highly appreciated!