sequelize中間テーブルマルチステート外部キー

const Sequelize =require('sequelize')
const sequelize = new Sequelize(
	'testdatabase', 
	'root', 
	'216612',
	{
        'dialect': 'mysql',  //      mysql
        'host': 'localhost', //       ip
        'port': 3306,        //         
        'define': {
            //       （_）   （         ）
            'underscored': true
        }
    });

const ItemTag = sequelize.define('item_tag', {
    id: {
            type: Sequelize.INTEGER,
            primaryKey: true,
            autoIncrement: true
        },
    tag_id: {
        type: Sequelize.INTEGER,
        unique: 'item_tag_taggable'
    },
    taggable: {
        type: Sequelize.STRING,
        unique: 'item_tag_taggable'
    },
    taggable_id: {
        type: Sequelize.INTEGER,
        unique: 'item_tag_taggable',
        references: null
    }
});
const Tag = sequelize.define('tag', {
    name: Sequelize.STRING
});
const Post = sequelize.define('post', {
    name: Sequelize.STRING
});
const Image = sequelize.define('image', {
    name: Sequelize.STRING
});

Post.belongsToMany(Tag, {
    through: {
        model: ItemTag,
        unique: false,
        scope: {
            taggable: 'post'
        }
    },
    foreignKey: 'taggable_id',
    constraints: false
});
Image.belongsToMany(Tag, {
    through: {
        model: ItemTag,
        unique: false,
        scope: {
            taggable: 'image'
        }
    },
    foreignKey: 'taggable_id',
    constraints: false
});
Tag.belongsToMany(Post, {
    through: {
        model: ItemTag,
        unique: false
    },
    foreignKey: 'tag_id',
    constraints: false
});
Tag.belongsToMany(Image, {
    through: {
        model: ItemTag,
        unique: false
    },
    foreignKey: 'tag_id',
    constraints: false 
});

let addTag=async ({name})=>{
	let tag=await Tag.create({name})
	return tag
}
let addPost=async ({name}) => {
	let post=await Post.create({name})
	return post
}
let addImage=async ({name})=>{
	let image=await Image.create({name})
	return image
}


	


sequelize.sync({force: true}).then(async function() {
	let tag1=await addTag({name:"normal"})
	let post1=await addPost({name:"post"})
	let post2=await addPost({name:"post"})
	let image1=await addImage({name:"image"})
	let image2=await addImage({name:"image"})
	//await tag1.addPost(post1,{through:{taggable:"post"}})
	await post1.addTag(tag1)
	//await tag1.addImage(image1,{through:{taggable:"image"}})
	await image1.addTag(tag1)
	//await tag1.addPost(post2,{through:{taggable:"post"}})
	await post2.addTag(tag1)
	//await tag1.addImage(image2,{through:{taggable:"image"}})
	await image2.addTag(tag1)



    return tag1
}).then(function(jane) {
    console.log(jane.get({
        plain: true
    }));
});

          id；

await post1.addTag(tag1)

await tag1.addPost(post1,{through:{taggable:"post"}})

taggable_id           ；