Node.js ORM - Sequelize

basic

Overview: ORM(Object Relation Mapping) based on Promise supports multiple databases, transactions, associations, etc
Installation: npm i sequelize mysql2 -S
Basic use:

const Sequelize = require("sequelize");

// Establish connection
const sequelize = new Sequelize("kaikeba", "root", "admin", {
    host: "localhost",
    dialect: "mysql",
    operatorsAliases: false
});

// Definition model
const Fruit = sequelize.define("Fruit", {
    name: {type: Sequelize.STRING(20), allowNull: false},
    price: {type: Sequelize.FLOAT, allowNull: false},
    stock: {type: Sequelize.INTEGER, defaultValue: 0}
});

// Synchronize database, force: true will delete the existing table
Fruit.sync().then(() => {
    // Add test data
    return Fruit.create({name: "Banana", price: 3.5});
}).then(() => {
    // Query
    Fruit.findAll().then(fruits => {
        console.log(JSON.stringify(fruits));
    });
});

What is forced synchronization? How to use it? (resets existing tables)

Fruit.sync({force: true})

Table is generated by default. How to remove it?

const Fruit = sequelize.define("Fruit", {}, {  timestamps: false });

Specify table name: freesetablename: true or tableName:'xxx'

Set the former to take modelName as the table name; set the latter to take its value as the table name.

What's the use of getters & setters? : can be used to define pseudo properties or protection properties mapped to database fields

// Defined as part of an attribute
name: {
    type: Sequelize.STRING, 
    allowNull :false, 
    get(){
        const fname = this.getDataValue("name");
        const price = this.getDataValue("price");
        const stock = this.getDataValue("stock");
        return `${fname}(Price:￥${price} Stock: ${stock}kg)`;
    }
}

// Define as model option 
{
    getterMethods:{
        amount()
        {
            return this.getDataValue("stock") + "kg";
        }
    },
    setterMethods:{
        amount(val)
        {
            const idx = val.indexOf('kg');
            const v = val.slice(0, idx);
            this.setDataValue('stock', v);
        }
    }
}

// Trigger setterMethods through model instance
Fruit.findAll().then(fruits => {
    console.log(JSON.stringify(fruits));
    // Modify amount and trigger setterMethods
    fruits[0].amount = '150kg';
    fruits[0].save();
});

How to verify? : the format and content of model fields can be verified through the verification function, and the verification will run automatically when creating, updating and saving

price: {
    validate: {
        isFloat: {msg: "Please enter a number for the price field"},
        min: {args: [0], msg:"Price field must be greater than 0"}
    }
},
stock: {
    validate: {
        isNumeric: {msg: "Please enter a number for the inventory field"}
    }
}

How to extend the model? : model instance method or class method extension model can be added

// Add class level method
Fruit.classify = function (name) {
    const tropicFruits = ['Banana', 'Mango', 'Coconut'];
    // Tropical fruit
    return tropicFruits.includes(name) ? 'Tropical fruits':'Other fruits'; };

// Add instance level method
    Fruit.prototype.totalPrice = function (count) {
        return (this.price * count).toFixed(2);
    };

// Using class methods
    ['Banana', 'Strawberry'].forEach(f => console.log(f + 'yes' + Fruit.classify(f)));

// Use instance method
    Fruit.findAll().then(fruits => {
        const [f1] = fruits;
        console.log(`Buy 5 kg${f1.name}Need￥${f1.totalPrice(5)}`);
    });

Additions and deletions

1 increase

    ret = await Fruit.create({
        name: "Banana",
        price: 3.5
    })

2 delete

// Mode 1 
Fruit.findOne({ where: { id: 1 } }).then(r => r.destroy());
 
// Mode 2 
Fruit.destroy({ where: { id: 1 } }).then(r => console.log(r));

3 changes

// Mode 1
Fruit.findById(1).then(fruit => {
    fruit.price = 4;
    fruit.save().then(() => console.log('update!!!!'));
});
// Mode 2 
Fruit.update({price: 4}, {where: {id: 1}}).then(r => {
    console.log(r);
    console.log('update!!!!')
})

4 check

// Query by attributes
Fruit.findOne({where: {name: "Banana"}}).then(fruit => {
    // fruit is the first match, null if not
    console.log(fruit.get());
});

// Get data and total number
Fruit.findAndCountAll().then(result => {
    console.log(result.count);
    console.log(result.rows.length);
});

// Query Operators 
const Op = Sequelize.Op;
Fruit.findAll({
// where: { price: { [Op.lt]:4 }, stock: { [Op.gte]: 100 } }  
    where: {price: {[Op.lt]: 4, [Op.gt]: 2}}
}).then(fruits => {
    console.log(fruits.length);
});

// Or statement
Fruit.findAll({
    // where: { [Op.or]:[{price: { [Op.lt]:4 }}, {stock: { [Op.gte]: 100 }}] }  
    where: {price: {[Op.or]: [{[Op.gt]: 3}, {[Op.lt]: 2}]}}
}).then(fruits => {
    console.log(fruits[0].get());
});

// paging
Fruit.findAll({offset: 0, limit: 2,})

// sort
Fruit.findAll({order: [['price', 'DESC']],})

// polymerization
setTimeout(() => {
    Fruit.max("price").then(max => {
        console.log("max", max)
    })
    Fruit.sum("price").then(sum => {
        console.log("sum", sum);
    });
}, 500)

4-2 associated query

Relation

//1:N relationship
const Player = sequelize.define('player', {name: Sequelize.STRING});
const Team = sequelize.define('team', {name: Sequelize.STRING});

// teamId will be added to Player table as foreign key
Player.belongsTo(Team);// 1 end building relationship
Team.hasMany(Player); // N-terminal relationship

// synchronization
sequelize.sync({force: true}).then(async () => {
    await Team.create({name: 'rocket'});
    await Player.bulkCreate([{name: 'Harden', teamId: 1}, {name: 'Paul', teamId: 1}]);
// 1 end Association query
    const players = await Player.findAll({include: [Team]});
    console.log(JSON.stringify(players, null, '\t'));
// N end Association query
    const team = await Team.findOne({where: {name: 'rocket'}, include: [Player]});
    console.log(JSON.stringify(team, null, '\t'));
});


// Many to many relationship
const Fruit = sequelize.define("fruit", {name: Sequelize.STRING});
const Category = sequelize.define("category", {name: Sequelize.STRING});
Fruit.FruitCategory = Fruit.belongsToMany(
    Category, {through: "FruitCategory"}
);