Specifying through.attributes does not filter columns in through tables

[chengluyu]

Issue Description

What are you doing?

Let's say we have three tables: users, tasks and participation. There's a n:m relation between users and tasks, which is based on the through table participations.

The through table has many columns. In some scenarios, only one of them is needed. So I write some query like this:

User.findAll({
  include: [Task.associations.tasks],
  through: {
    attributes: ['role']
  }
})

But the query result still contains all columns. I also found this issue: #5590. But includeIgnoreAttributes seems doesn't work at all.

Here is the link to the SSCCE for this issue: sequelize/sequelize-sscce#33

What do you expect to happen?

The generated SQL query should only contain column role in table participations.

What is actually happening?

The generated SQL query contains all columns in table participations. A direct link to this line in CI output. Below is a formatted one.

SELECT
    `users`.`id`,
    `users`.`username`,
    `users`.`createdAt`,
    `users`.`updatedAt`,
    `tasks`.`id` AS `tasks.id`,
    `tasks`.`name` AS `tasks.name`,
    `tasks`.`description` AS `tasks.description`,
    `tasks`.`createdAt` AS `tasks.createdAt`,
    `tasks`.`updatedAt` AS `tasks.updatedAt`,
    `tasks->participates`.`id` AS `tasks.participates.id`, -- this line shouldn't exist
    `tasks->participates`.`role` AS `tasks.participates.role`,
    `tasks->participates`.`createdAt` AS `tasks.participates.createdAt`, -- this line shouldn't exist
    `tasks->participates`.`updatedAt` AS `tasks.participates.updatedAt`, -- this line shouldn't exist
    `tasks->participates`.`userId` AS `tasks.participates.userId`, -- this line shouldn't exist
    `tasks->participates`.`taskId` AS `tasks.participates.taskId` -- this line shouldn't exist
FROM
    `users` AS `users`
    LEFT OUTER JOIN `participates` AS `tasks->participates` ON `users`.`id` = `tasks->participates`.`taskId`
    LEFT OUTER JOIN `tasks` AS `tasks` ON `tasks`.`id` = `tasks->participates`.`userId`;

Additional context

Add any other context or screenshots about the feature request? Nope.

Environment

• Sequelize version: sequelize@5.21.3
• Node.js version: v13.5.0
• Operating System: macOS Catalina 10.15.2 (19C57)
• TypeScript: not related.

Issue Template Checklist

How does this problem relate to dialects?

• I think this problem happens regardless of the dialect.
• I think this problem happens only for the following dialect(s):
• I don't know, I was using PUT-YOUR-DIALECT-HERE, with connector library version XXX and database version XXX

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don't know how to start, I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.

[theRichu]

Hello, I found in query-generator.js

    const throughAttributes = through.attributes.map(attr => {

    const throughAttributes = (through.originalAttributes || through.attributes).map(attr => {

I checked it works, but not well tested

I wish it helps

[papb]

See sequelize/website#97

[github-actions]

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