### db/config.js
```
module.exports = {
    "username": "postgres",
    "password": "password",
    "database": "diary",
    "dialect": "postgres",
    "protocol": "postgres",
    "port": 5432,
    "host": "127.0.0.1",
};
```

### db/index.js
```
const Sequelize = require('sequelize');
const config = require('./config');

const sequelize = new Sequelize(
    config.database, config.username, config.password, config
);

sequelize
    .authenticate()
    .then(() => {
        console.log('Connection to database has been established successfully.');
    })
    .catch(err => {
        console.error('Unable to connect to the database:', err);
    });

module.exports = {sequelize};
```

### db/models/student.js
```
module.exports = (sequelize, DataTypes) => {
    const Student = sequelize.define('Student', {
        name:{
            type: DataTypes.STRING,
            allowNull: false,
        }
    });

    Student.associate = (models) => {
        Student.belongsTo(models.Group, {
            foreignKey: 'group_id',
            as: 'group'
        });
    };

    return Student;
};
```

### db/models/group.js
```
module.exports = (sequelize, DataTypes) => {
    const Group = sequelize.define('Group', {
        name: {
            type: DataTypes.STRING,
            allowNull: false,
            unique: true
        }
    });

    Group.associate = (models) => {
        Group.hasMany(models.Student, {
            foreignKey: 'group_id',
            as: 'students',
        });
    };

    return Group;
};
```

### db/models/index.js
```
const {sequelize} = require('./../index');
const models = [
    sequelize.import('./student'),
    sequelize.import('./group')
];

module.exports = initModels(sequelize);

function initModels(sequelize) {
    const result = {};
    models.forEach((model) => {
        result[model.name] = model;
    });

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

    sequelize.sync();

    return result;
}
```

### Then you can import models in your app like this:
```
const Group = require('./db/models/index').Group;
const Student = require('./db/models/index').Student;
```