问在已部署的数据库中创建两个表之间的新关系

EN

module.exports = {
  up: (queryInterface, Sequelize) => {
    return queryInterface.addColumn("students", "school_id", {
      type: Sequelize.DataTypes.INTEGER,
        /*
          The defaultValue below was assigned because by default constraints are set to true.
          This means that all students must belong to a school
          If no school_id is specified, mysql sees that this does not follow the constraints and will opt to delete all records from the database.
          So assign a default value and after this, you can go ahead to manually assign the correct schools.
          ENSURE THAT THE DEFAULT VALUE OF school_id PROVIDED HAS A CORRESPONDING EXISITING RECORD IN THE school TABLE
        */
      defaultValue: 1, // or any other existing value. (This is very important!)
      references: {
        model: "schools",
        key: "school_id",
      },
    });
  },
  down: (queryInterface, Sequelize) => {
    return queryInterface.removeColumn("students", "school_id");
  },
};