Sequelize validation with increment function - node.js

Question

There's a sequelize function that allows to increment a value by a number, that number can be negative to decrement, I would like to make sure that that column is always positive or 0, so I added a validator to my model:
module.exports = function (sequelize, DataTypes) {
var ProductVariant = sequelize.define('ProductVariant', {
id: {
type: DataTypes.INTEGER(11),
allowNull: false,
primaryKey: true,
autoIncrement: true
},
ProductId: {
type: DataTypes.STRING(45),
field: 'product_id',
allowNull: false,
primaryKey: true,
references: {
model: 'product',
key: 'id'
}
},
image: {
type: DataTypes.INTEGER(11),
allowNull: true
},
price: {
type: DataTypes.DECIMAL(6, 2),
allowNull: false
},
qty_stock: {
type: DataTypes.INTEGER(11),
allowNull: false,
defaultValue: 0
},
createdAt: {
type: 'TIMESTAMP',
allowNull: true,
field: 'creation_date'
},
updatedAt: {
type: 'TIMESTAMP',
field: 'last_updated',
allowNull: true
},
},
{
tableName: 'variants',
hooks: {
beforeValidate: function(variant, options) {
if (variant.qty_assigned < 0) {
throw new Error('Not valid');
}
}
}
});
ProductVariant.associate = function (models) {
ProductVariant.belongsTo(models.Product)
},
{
indexes:
[{
unique: true,
fields: ['product_id']
}]
}
return ProductVariant;
};
But when I do:
await ProductVariant.increment({ qty_assigned: -100 }, {
where: { id: { [Op.eq]: variantId } },
transaction: t
});
I works and updates the value without checking validation. I also tried with:
qty_stock: {
type: DataTypes.INTEGER(11),
allowNull: false,
defaultValue: 0,
validate: {
min: 0
}
}
Is it possible that is has to do with the fact that increment is done in database? can I do something to add a validation?

Answer 1

Validation is done against an instance (in your app) and not against the DB.
The increment API is special as it updates the value directly in the database and not on the instance
From https://sequelize.org/master/class/lib/model.js~Model.html#static-method-increment (emphasis mine)
Increment the value of one or more columns. This is done in the database, which means it does not use the values currently stored on the Instance. The increment is done using a SET column = column + X WHERE foo = 'bar' query. To get the correct value after an increment into the Instance you should do a reload.
If you want to increment and get validation done, you can:
use a transaction (or optimistic locking) and update manually increment the value of the instance (use sequelize validation)
add a check in the DB (mysql8+: https://dev.mysql.com/doc/refman/8.0/en/create-table-check-constraints.html).