more sequelize will it ever end

rootfs_overlay/lkmc/nodejs/sequelize/association_nested_include.js

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+#!/usr/bin/env node
+
+// Find all posts by users that a given user follows.
+// https://stackoverflow.com/questions/42632943/sequelize-multiple-where-clause
+
+const assert = require('assert');
+const path = require('path');
+
+const { Sequelize, DataTypes } = require('sequelize');
+
+const sequelize = new Sequelize({
+  dialect: 'sqlite',
+  storage: 'tmp.' + path.basename(__filename) + '.sqlite',
+});
+
+(async () => {
+
+// Create the tables.
+const User = sequelize.define('User', {
+  name: { type: DataTypes.STRING },
+}, {});
+const Post = sequelize.define('Post', {
+  body: { type: DataTypes.STRING },
+}, {});
+User.belongsToMany(User, {through: 'UserFollowUser', as: 'Follows'});
+User.hasMany(Post);
+Post.belongsTo(User);
+await sequelize.sync({force: true});
+
+// Create data.
+const users = await User.bulkCreate([
+  {name: 'user0'},
+  {name: 'user1'},
+  {name: 'user2'},
+  {name: 'user3'},
+])
+
+const posts = await Post.bulkCreate([
+  {body: 'body00', UserId: users[0].id},
+  {body: 'body11', UserId: users[0].id},
+  {body: 'body10', UserId: users[1].id},
+  {body: 'body11', UserId: users[1].id},
+  {body: 'body20', UserId: users[2].id},
+  {body: 'body21', UserId: users[2].id},
+  {body: 'body30', UserId: users[3].id},
+  {body: 'body31', UserId: users[3].id},
+])
+
+await users[0].addFollows([users[1], users[2]])
+
+// Get all posts by authors that user0 follows.
+// The posts are placed inside their respetive authors under .Posts
+// so we loop to gather all of them.
+{
+  const user0Follows = (await User.findByPk(users[0].id, {
+    include: [
+      {
+        model: User,
+        as: 'Follows',
+        include: [
+          {
+            model: Post,
+          }
+        ],
+      },
+    ],
+  })).Follows
+  const postsFound = []
+  for (const followedUser of user0Follows) {
+    postsFound.push(...followedUser.Posts)
+  }
+  postsFound.sort((x, y) => { return x.body < y.body ? -1 : x.body > y.body ? 1 : 0 })
+  assert(postsFound[0].body === 'body10')
+  assert(postsFound[1].body === 'body11')
+  assert(postsFound[2].body === 'body20')
+  assert(postsFound[3].body === 'body21')
+  assert(postsFound.length === 4)
+}
+
+// With ordering, offset and limit.
+// The posts are placed inside their respetive authors under .Posts
+// The only difference is that posts that we didn't select got removed.
+
+{
+  const user0Follows = (await User.findByPk(users[0].id, {
+    offset: 1,
+    limit: 2,
+    // TODO why is this needed? It does try to make a subquery otherwise, and then it doesn't work.
+    // https://selleo.com/til/posts/ddesmudzmi-offset-pagination-with-subquery-in-sequelize-
+    subQuery: false,
+    include: [
+      {
+        model: User,
+        as: 'Follows',
+        include: [
+          {
+            model: Post,
+          }
+        ],
+      },
+    ],
+  })).Follows
+  assert(user0Follows[0].name === 'user1')
+  assert(user0Follows[1].name === 'user2')
+  assert(user0Follows.length === 2)
+  const postsFound = []
+  for (const followedUser of user0Follows) {
+    postsFound.push(...followedUser.Posts)
+  }
+  postsFound.sort((x, y) => { return x.body < y.body ? -1 : x.body > y.body ? 1 : 0 })
+  // Note that what happens is that some of the
+  assert(postsFound[0].body === 'body11')
+  assert(postsFound[1].body === 'body20')
+  assert(postsFound.length === 2)
+
+  // Same as above, but now with DESC ordering.
+  {
+    const user0Follows = (await User.findByPk(users[0].id, {
+      order: [[
+        {model: User, as: 'Follows'},
+        Post,
+        'body',
+        'DESC'
+      ]],
+      offset: 1,
+      limit: 2,
+      subQuery: false,
+      include: [
+        {
+          model: User,
+          as: 'Follows',
+          include: [
+            {
+              model: Post,
+            }
+          ],
+        },
+      ],
+    })).Follows
+    // Note how user ordering is also reversed from an ASC.
+    // it likely takes the use that has the first post.
+    assert(user0Follows[0].name === 'user2')
+    assert(user0Follows[1].name === 'user1')
+    assert(user0Follows.length === 2)
+    const postsFound = []
+    for (const followedUser of user0Follows) {
+      postsFound.push(...followedUser.Posts)
+    }
+    // In this very specific data case, this would not be needed.
+    // because user2 has the second post body and user1 has the first
+    // alphabetically.
+    postsFound.sort((x, y) => { return x.body < y.body ? 1 : x.body > y.body ? -1 : 0 })
+    // Note that what happens is that some of the
+    assert(postsFound[0].body === 'body20')
+    assert(postsFound[1].body === 'body11')
+    assert(postsFound.length === 2)
+  }
+
+  // Here user2 would have no post hits due to the limit,
+  // so it is entirely pruned from the user list as desired.
+  // Otherwise we would fetch a lot of unwanted user data
+  // in a large database.
+  const user0FollowsLimit2 = (await User.findByPk(users[0].id, {
+    limit: 2,
+    subQuery: false,
+    include: [
+      {
+        model: User,
+        as: 'Follows',
+        include: [ { model: Post } ],
+      },
+    ],
+  })).Follows
+  assert(user0FollowsLimit2[0].name === 'user1')
+  assert(user0FollowsLimit2.length === 1)
+
+  // Case in which our post-sorting is needed.
+  // TODO: possible to get sequelize to do this for us by returning
+  // a flat array directly?
+  // It's not big deal since the LIMITed result should be small,
+  // but feels wasteful.
+  // https://stackoverflow.com/questions/41502699/return-flat-object-from-sequelize-with-association
+  // https://github.com/sequelize/sequelize/issues/4419
+  {
+    await Post.truncate({restartIdentity: true})
+    const posts = await Post.bulkCreate([
+      {body: 'body0', UserId: users[0].id},
+      {body: 'body1', UserId: users[1].id},
+      {body: 'body2', UserId: users[2].id},
+      {body: 'body3', UserId: users[3].id},
+      {body: 'body4', UserId: users[0].id},
+      {body: 'body5', UserId: users[1].id},
+      {body: 'body6', UserId: users[2].id},
+      {body: 'body7', UserId: users[3].id},
+    ])
+    const user0Follows = (await User.findByPk(users[0].id, {
+      order: [[
+        {model: User, as: 'Follows'},
+        Post,
+        'body',
+        'DESC'
+      ]],
+      subQuery: false,
+      include: [
+        {
+          model: User,
+          as: 'Follows',
+          include: [
+            {
+              model: Post,
+            }
+          ],
+        },
+      ],
+    })).Follows
+    assert(user0Follows[0].name === 'user2')
+    assert(user0Follows[1].name === 'user1')
+    assert(user0Follows.length === 2)
+    const postsFound = []
+    for (const followedUser of user0Follows) {
+      postsFound.push(...followedUser.Posts)
+    }
+    // We need this here, otherwise we would get all user2 posts first:
+    // body6, body2, body5, body1
+    postsFound.sort((x, y) => { return x.body < y.body ? 1 : x.body > y.body ? -1 : 0 })
+    assert(postsFound[0].body === 'body6')
+    assert(postsFound[1].body === 'body5')
+    assert(postsFound[2].body === 'body2')
+    assert(postsFound[3].body === 'body1')
+    assert(postsFound.length === 4)
+  }
+}
+
+await sequelize.close();
+})();