Why does sequelize 5 do this?

Question

Good day! When I am creating associations between models User and Test, sequelize works fine. But when I want add new associations for Test and Question, then sequelize add new column (my foreign key test_id and extra testId ).

Why?

user.js

module.exports = (sequelize, DataType) => {
  const User = sequelize.define('user', {
    username: {
      type: DataType.STRING,
      unique: true,
    },
    password: {
      type: DataType.STRING,
    },
  });

  User.associate = (models) => {
    User.hasMany(models.test, {
      foreignKey: 'id',
    });
  };

  return User;
};

test.js

module.exports = (sequelize, DataType) => {
  const Test = sequelize.define('test', {
    title: {
      type: DataType.STRING,
      unique: true,
      required: true,
    },

    description: {
      type: DataType.TEXT,
      required: true,
    },

    picture: { // picture link
      type: DataType.STRING,
    },
  });

  Test.associate = (models) => {
    Test.belongsTo(models.user, {
      foreignKey: 'user_id',
    });
  };

  Test.associate = (models) => {
    Test.hasMany(models.question, {
      foreign_key: 'id',
    });
  };

  return Test;
};

question.js

module.exports = (sequelize, DataType) => {
  const Question = sequelize.define('question', {
    title: {
      type: DataType.STRING,
      required: true,
    },
  });

  Question.associate = (models) => {
    Question.belongsTo(models.test, {
      foreignKey: 'test_id',
    });
  };
  return Question;
};

index.js

const fs = require('fs');
const path = require('path');
const Sequelize = require('sequelize');
require('dotenv').config();

const config = process.env;
const basename = path.basename(module.filename);

const sequelize = new Sequelize({
  database: config.DB_NAME,
  username: config.DB_USER,
  password: config.DB_PASS,
  dialect: config.DB_DIALECT,
});
const db = {};

fs
  .readdirSync(__dirname)
  .filter(file => (file.indexOf('.') !== 0) && (file !== basename))
  .forEach((file) => {
    const model = sequelize.import(path.join(__dirname, file));
    db[model.name] = model;
  });

Object.keys(db).forEach((modelName) => {
  if (db[modelName].associate) {
    db[modelName].associate(db);
  }
});

Object.keys(db).forEach((modelName) => {
  if ('loadScopes' in db[modelName]) {
    db[modelName].loadScopes(db);
  }
});

db.sequelize = sequelize;
db.Sequelize = Sequelize;

module.exports = db;

These models generate some SQL queries:

Executing (default): CREATE TABLE IF NOT EXISTS `users` (`id` INTEGER NOT NULL auto_increment , `username` VARCHAR(255) UNIQUE, `password` VARCHAR(255), `createdAt` DATETIME NOT NULL, `updatedAt` DATETIME NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB;

Executing (default): SHOW INDEX FROM `users` FROM `nrforms`

Executing (default): CREATE TABLE IF NOT EXISTS `tests` (`id` INTEGER NOT NULL auto_increment , `title` VARCHAR(255) UNIQUE, `description` TEXT, `picture` VARCHAR(255), `createdAt` DATETIME NOT NULL, `updatedAt` DATETIME NOT NULL, PRIMARY KEY (`id`), FOREIGN KEY (`id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE) ENGINE=InnoDB;

Executing (default): SHOW INDEX FROM `tests` FROM `nrforms`

Executing (default): CREATE TABLE IF NOT EXISTS `questions` (`id` INTEGER NOT NULL auto_increment , `title` VARCHAR(255), `createdAt` DATETIME NOT NULL, `updatedAt` DATETIME NOT NULL, `test_id` INTEGER, `testId` INTEGER, PRIMARY KEY (`id`), FOREIGN KEY (`test_id`) REFERENCES `tests` (`id`) ON DELETE SET NULL ON UPDATE CASCADE, FOREIGN KEY (`testId`) REFERENCES `tests` (`id`) ON DELETE SET NULL ON UPDATE CASCADE) ENGINE=InnoDB;

Executing (default): SHOW INDEX FROM `questions` FROM `nrforms`

Answer 1

I found a problem.

  Test.associate = (models) => {
    Test.hasMany(models.question, {
      foreignKey: 'id', // was foreign_key: 'id' 
    });
  };

May be is it a bug or trigger for autocreate reverse association? But i doesn't found information about that.

Answer 2

Add underscored: false in all your models:

module.exports = (sequelize, DataType) => {
    const Question = sequelize.define('question', {
        title: {
            type: DataType.STRING,
            required: true,
        },
    },
        {
            underscored: false, // <---- add this in all your models
        });

    Question.associate = (models) => {
        Question.belongsTo(models.test, {
            foreignKey: 'test_id',
        });
    };
    return Question;
};

Sequelize Documentation reference