Issue with relations in SequelizeJS

I get an issue using relations in SequelizeJS.

My error message : (500 : Internal Server Error) user is not associated to article!

Article model :

var Article = db.define('article', {

    title: {
        type: Types.STRING,
    },

    content: {
        type: Types.TEXT,
    },
},{
    classMethods:{
        associate: function (models) {
            Article.belongsTo(models.User, {as: 'Author'});
        }
    }
});

User model :

var User = db.define('user', {

    username: {
        type: Types.STRING,
    },

    email: {
        type: Types.STRING,
    },

    password: {
        type: Types.STRING
    },
},{
    classMethods:{
        associate: function (models) {
            User.hasMany(models.Article, {as: 'Articles'});
        }
    }
});

And my include query :

getAll: function (callback) {
    return this.context.Article.findAll({include: [this.context.User]});
},