title: Getting DatabaseError [SequelizeDatabaseError] ,incorrect integer value
body: <p>I am trying to develop a mini shopping site, wherein I am doing this using NodeJs Express and MySQL</p>
  
  <p>my cart could have many products and each product could belong to multiple carts.</p>
  
  <p>Therefore using sequelize,my relations are as follows:</p>
  
  <pre><code>Cart.belongsToMany(Product, { through: CartItem });
  Product.belongsToMany(Cart, { through: CartItem });
  </code></pre>
  
  <p>Now CartItem is another table that maps between cartid and productid.</p>
  
  <p>Each of these table have been designed as follows.</p>
  
  <p><strong>Product</strong></p>
  
  <pre><code>const Sequelize = require('sequelize');
  
      const sequelize = require('../util/database');
  
      const Product = sequelize.define('product', {
        id: {
          type: Sequelize.INTEGER,
          autoIncrement: true,
          allowNull: false,
          primaryKey: true
        },
        title: Sequelize.STRING,
        price: {
          type: Sequelize.DOUBLE,
          allowNull: false
        },
        imageUrl: {
          type: Sequelize.STRING,
          allowNull: false
        },
        description: {
          type: Sequelize.STRING,
          allowNull: false
        }
      });
  
      module.exports = Product;
  </code></pre>
  
  <p><strong>Cart</strong></p>
  
  <pre><code>const Sequelize = require('sequelize');
  
  const sequelize = require('../util/database');
  
  const Cart = sequelize.define('cart', {
    id: {
      type: Sequelize.INTEGER,
      autoIncrement: true,
      allowNull: false,
      primaryKey: true
    }
  });
  
  module.exports = Cart;
  </code></pre>
  
  <p><strong>CartItem</strong></p>
  
  <pre><code>const Sequelize = require('sequelize');
  
  const sequelize = require('../util/database');
  
  const CartItem = sequelize.define('cartItem', {
    id: {
      type: Sequelize.INTEGER,
      autoIncrement: true,
      allowNull: false,
      primaryKey: true
    },
    quantity: Sequelize.INTEGER
  });
  
  module.exports = CartItem;
  </code></pre>
  
  <p>I am trying to add a product to my cart. The logic is to retrieve the list of all available items in the cart. If the product that I am adding already exists, then I just increase the quantity.Else I add it afresh.</p>
  
  <p>The code to do that is as follows:</p>
  
  <pre><code>module.exports.postCart = (req, res, next) =&gt; {
      const prodId = req.body.productId;
      let fetchedCart;
      let qty=1;
      req.user.getCart()
          .then(cart =&gt; {
              fetchedCart = cart;
              console.log('cart', cart);
              return cart.getProducts({where:{id:prodId}});
          })
          .then(products =&gt; {
              let productInCart;
              if (products.length &gt; 0) {
                  productInCart = products[0];
              }
              if (productInCart) {
                  const oldQuantity = productInCart.cartItem.quantity;
                  qty = oldQuantity + 1;
                  return productInCart;
                }
                //console.log(Product.findByPk(prodId));
                return Product.findByPk(prodId);
          })
          .then(product =&gt; {
              console.log('product',product);
  
              return fetchedCart.addProduct(product, {
                  through: { quantity: qty }
                });
          })
          .then(() =&gt; {
              res.redirect('/cart');
            })
          .catch(err =&gt; {
              console.log(err);
          })
  };
  </code></pre>
  
  <p>Problem is that whenever I try to add a particular product to cart ,I end up with this error. I can see solutions to a lot of similar usecases here,but not related to the problem that I am facing at the moment.</p>
  
  <p>Error Stack Trace.</p>
  
  <pre><code>Executing (default): SELECT `id`, `quantity`, `createdAt`, `updatedAt`, `cartId`, `productId` FROM 
  
  `cartItems` AS `cartItem` WHERE `cartItem`.`cartId` = 1 AND `cartItem`.`productId` IN ('[object SequelizeInstance:product]');
  
  Executing (default): INSERT INTO `cartItems` (`id`,`quantity`,`createdAt`,`updatedAt`,`cartId`,`productId`) VALUES (NULL,1,'2020-02-22 07:39:45','2020-02-22 07:39:45',1,'[object SequelizeInstance:product]');
  DatabaseError [SequelizeDatabaseError]: Incorrect integer value: '[object SequelizeInstance:product]' 
  
  
  for column 'productId' at row 1    at Query.formatError (C:\Users\Aravind\Documents\workspace-VSC\node_modules\sequelize\lib\dialects\mysql\query.js:244:16)
      at Query.handler [as onResult] (C:\Users\Aravind\Documents\workspace-VSC\node_modules\sequelize\lib\dialects\mysql\query.js:51:23)
      at Query.execute (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\commands\command.js:30:14)
      at Connection.handlePacket (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:417:32)
      at PacketParser.onPacket (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:75:12)
      at PacketParser.executeStart (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\packet_parser.js:75:16)
      at Socket.&lt;anonymous&gt; (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:82:25)
      at Socket.emit (events.js:210:5)
      at addChunk (_stream_readable.js:309:12)
      at readableAddChunk (_stream_readable.js:290:11)
      at Socket.Readable.push (_stream_readable.js:224:10)
      at TCP.onStreamRead (internal/stream_base_commons.js:182:23) {
    name: 'SequelizeDatabaseError',
  
    parent: Error: Incorrect integer value: '[object SequelizeInstance:product]' for column 'productId' at row 1
        at Packet.asError (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\packets\packet.js:712:17)
        at Query.execute (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\commands\command.js:28:26)
        at Connection.handlePacket (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:417:32)
        at PacketParser.onPacket (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:75:12)
        at PacketParser.executeStart (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\packet_parser.js:75:16)
        at Socket.&lt;anonymous&gt; (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:82:25)
        at Socket.emit (events.js:210:5)
        at addChunk (_stream_readable.js:309:12)
        at readableAddChunk (_stream_readable.js:290:11)
        at Socket.Readable.push (_stream_readable.js:224:10)
        at TCP.onStreamRead (internal/stream_base_commons.js:182:23) {
      code: 'ER_TRUNCATED_WRONG_VALUE_FOR_FIELD',
      errno: 1366,
      sqlState: 'HY000',
      sqlMessage: "Incorrect integer value: '[object SequelizeInstance:product]' for column 'productId' at row 1",
  
  
  
        sql: "INSERT INTO `cartItems` (`id`,`quantity`,`createdAt`,`updatedAt`,`cartId`,`productId`) VALUES (NULL,1,'2020-02-22 07:39:45','2020-02-22 07:39:45',1,'[object SequelizeInstance:product]');",
          parameters: undefined
  
    },
  
    original: Error: Incorrect integer value: '[object SequelizeInstance:product]' for column 'productId' at row 1
        at Packet.asError (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\packets\packet.js:712:17)
        at Query.execute (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\commands\command.js:28:26)
        at Connection.handlePacket (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:417:32)
        at PacketParser.onPacket (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:75:12)
        at PacketParser.executeStart (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\packet_parser.js:75:16)
        at Socket.&lt;anonymous&gt; (C:\Users\Aravind\Documents\workspace-VSC\node_modules\mysql2\lib\connection.js:82:25)
        at Socket.emit (events.js:210:5)
        at addChunk (_stream_readable.js:309:12)
        at readableAddChunk (_stream_readable.js:290:11)
        at Socket.Readable.push (_stream_readable.js:224:10)
        at TCP.onStreamRead (internal/stream_base_commons.js:182:23) {
      code: 'ER_TRUNCATED_WRONG_VALUE_FOR_FIELD',
      errno: 1366,
      sqlState: 'HY000',
      sqlMessage: "Incorrect integer value: '[object SequelizeInstance:product]' for column 'productId' at row 1",
      sql: "INSERT INTO `cartItems` (`id`,`quantity`,`createdAt`,`updatedAt`,`cartId`,`productId`) VALUES (NULL,1,'2020-02-22 07:39:45','2020-02-22 07:39:45',1,'[object SequelizeInstance:product]');",
      parameters: undefined
    },
    sql: "INSERT INTO `cartItems` (`id`,`quantity`,`createdAt`,`updatedAt`,`cartId`,`productId`) VALUES (NULL,1,'2020-02-22 07:39:45','2020-02-22 07:39:45',1,'[object SequelizeInstance:product]');",
    parameters: undefined
  }
  </code></pre>
  
  <p><strong>Can someone please tell me what wrong I am doing here. I am able to console.log() the value of product as follows, which I think is correct.</strong></p>
  
  <pre><code>product product {
    dataValues: {
      id: 1,
      title: "Children's book",
      price: 20,
      imageUrl: 'orth-dakota-sunflower.jpg',
      description: 'https://dynai5135742-02-n',
      createdAt: 2020-02-22T10:05:22.000Z,
      updatedAt: 2020-02-22T10:05:22.000Z
    },
    _previousDataValues: {
      id: 1,
      title: "Children's book",
      price: 20,
      imageUrl: 'orth-dakota-sunflower.jpg',
      description: 'https://dynai5135742-02-n',
      createdAt: 2020-02-22T10:05:22.000Z,
      updatedAt: 2020-02-22T10:05:22.000Z
    },
    _changed: {},
    _modelOptions: {
      timestamps: true,
      validate: {},
      freezeTableName: false,
      underscored: false,
      paranoid: false,
      rejectOnEmpty: false,
      whereCollection: { id: '1' },
      schema: null,
      schemaDelimiter: '',
      defaultScope: {},
      scopes: {},
      indexes: [],
      name: { plural: 'products', singular: 'product' },
      omitNull: false,
      sequelize: Sequelize {
        options: [Object],
        config: [Object],
        dialect: [MysqlDialect],
        queryInterface: [QueryInterface],
        models: [Object],
        modelManager: [ModelManager],
        connectionManager: [ConnectionManager],
        importCache: {}
      },
      hooks: {}
    },
    _options: {
      isNewRecord: false,
      _schema: null,
      _schemaDelimiter: '',
      raw: true,
      attributes: [
        'id',
        'title',
        'price',
        'imageUrl',
        'description',
        'createdAt',
        'updatedAt'
      ]
    },
    isNewRecord: false
  }
  </code></pre>
  
  <p>Thanks in advance.</p>