Can't link tables via Sequelize, why?

Question

JavaScript

There are two
category tables:

module.exports = (sequelize, DataTypes) => {
  const category = sequelize.define('category', {
    title: DataTypes.STRING,

  }, {});
  category.associate = function(models) {
    category.hasMany(models.post, {
      foreignKey: 'post_id',
      as: 'articles'
    });
  };
  return category;
};

post:

module.exports = (sequelize, DataTypes) => {
  const post = sequelize.define('post', {
    title: DataTypes.STRING,
  
}, {});
  post.associate = function(models) {
    post.belongsTo(models.category, {
      foreignKey: 'post_id'
    });
  };
  return post;
};

Why after sequelize db:migrate in the table with categories in the post_id column there is an integer and a field if there is data in the post table?