Foreign key by default is null

[mdrokz]

Issue Description

I was going through the association docs to create foreign key constraints for my tables in sqlite but i noticed when using Model.HasMany(Child) by default the foreign key definition is allowNull: true which defeats the purpose of using a foreign key constraint.

https://sequelize.org/docs/v6/core-concepts/assocs/

Im not sure if i missed anything but i couldnt find this anywhere in the docs and the associations docs doesnt explain this behavior properly.

Let me know if i'm missing anything

Additional context

This code would define the foreign key employeeId with allowNull:true

sequelize.define("Employees", {
    id: {
        type: DataTypes.UUIDV4,
        defaultValue: DataTypes.UUIDV4,
        primaryKey: true,
    },
    name: {
        type: DataTypes.STRING,
        allowNull: false
    },
    employeeType: {
        type: DataTypes.INTEGER,
        allowNull: false
    }

}, {
    indexes: [
        {
            using: "BTREE",
            fields: ["employeeType"]
        }
    ]
})


sequelize.define("Missions", {
    id: {
        type: DataTypes.UUIDV4,
        defaultValue: DataTypes.UUIDV4,
        primaryKey: true,
    },
    hours: {
        type: DataTypes.INTEGER,
        allowNull: false
    },
    missionName: {
        type: DataTypes.STRING,
        allowNull: true
    },
    missionDate: {
        type: DataTypes.DATE,
        allowNull: false
    },
    missionType: {
        type: DataTypes.INTEGER,
        allowNull: true
    }
}
);


// 1 to many relationship between employees & missions
sequelize.models.Employees.hasMany(sequelize.models.Missions);

I had to refactor the code to this for the foreign key constraint to be effective

sequelize.define("Employees", {
    id: {
        type: DataTypes.UUIDV4,
        defaultValue: DataTypes.UUIDV4,
        primaryKey: true,
    },
    name: {
        type: DataTypes.STRING,
        allowNull: false
    },
    employeeType: {
        type: DataTypes.INTEGER,
        allowNull: false
    }

}, {
    indexes: [
        {
            using: "BTREE",
            fields: ["employeeType"]
        }
    ]
})


sequelize.define("Missions", {
    id: {
        type: DataTypes.UUIDV4,
        defaultValue: DataTypes.UUIDV4,
        primaryKey: true,
    },
    employeeId: {
        type: DataTypes.UUIDV4,
        allowNull: false,
    },
    hours: {
        type: DataTypes.INTEGER,
        allowNull: false
    },
    missionName: {
        type: DataTypes.STRING,
        allowNull: true
    },
    missionDate: {
        type: DataTypes.DATE,
        allowNull: false
    },
    missionType: {
        type: DataTypes.INTEGER,
        allowNull: true
    }
}
);


// 1 to many relationship between employees & missions
sequelize.models.Employees.hasMany(sequelize.models.Missions, {
    foreignKey: 'employeeId',
    as: 'missions'
});