Firebase Schema

Denormalizing your Data Store for Firebase

• 在Firebase上存的資料是jason的文件
• 資料項目是以key-value的格式表示，value的值可以是數字/字串/其他物件，但是不支援array。
• 當要建構Firebase資料庫時，記住下列兩個規則：
• 讓資料的階層淺一點(shallow)
• 不要怕重複的資料

• Firebase上的資料是以URL的方式來存取
• 若我建了一個主要的project叫`Uber for Dogs`，他就會存在於此網址：https://uber-for-dogs.firebaseio.com/
• 若我存了一個物件如下

{
  name: 'Anthony'
}

• 那麼我就可以在 https://uber-for-dogs.firebaseio.com/name取得Anthony這個字串
• 假設資料更複雜一點如下，想要查詢某個user時只要去/users/some-user-id查詢還蠻方便。但若是想查詢某篇文章，而且資料內有很多個user，那就必須要查過所有user才能找到該篇文章。

users: {
    tylermcginis: {
        name: 'Tyler McGinnis',
        age: 25,
        posts: {
            post1: {
                title: 'What is a jQuery',
                date: 1461131626103,
                likes: {
                    'jakelingwall': true,
                    'eanplatter': true,
                    'mikenzi': true
                },
                replies: {
                    reply1: {
                        name: 'Jake Lingwall',
                        comment: 'Its a monad',
                        id: 'jakelingwall'
                    },
                    reply2: {
                        name: 'Ean Platter',
                        comment: 'Its a type of Java',
                        id: 'eanplatter'
                    }
                }
            }
        }
    }
}

• 你可以將資料改成下列格式，讓重複的資料來加快尋找特定文章的速度，但重複的資料又會有資料是否能sync的困難點。

users: {
    tylermcginis: {
        name: 'Tyler McGinnis',
        age: 25,
        posts: {
            post1: {
                title: 'What is a jQuery',
                date: 1461131626103,
                likes: {
                    'jakelingwall': true,
                    'eanplatter': true,
                    'mikenzi': true
                },
                replies: {
                    reply1: {
                        name: 'Jake Lingwall',
                        comment: 'Its a monad',
                        id: 'jakelingwall'
                    },
                    reply2: {
                        name: 'Ean Platter',
                        comment: 'Its a type of Java',
                        id: 'eanplatter'
                    }
                }
            }
        }
    }
},
posts: {
    post1:{
        title: 'What is a jQuery',
        date: 1461131626103,
        likes: {
            'jakelingwall': true,
            'eanplatter': true,
            'mikenzi': true
        },
        replies: {
            reply1: {
                name: 'Jake Lingwall',
                comment: 'Its a monad',
                id: 'jakelingwall'
            },
            reply2: {
                name: 'Ean Platter',
                comment: 'Its a type of Java',
                id: 'eanplatter'
            }
        }
    }
}

• 下面的資料格式則是讓資料階層變很淺，並且把重複的資料移除，但要查詢某篇文章時，必須送出三個request (posts/replies/likes)，所以這個方式也不是最好的

users: {
    tylermcginis: {
        name: 'Tyler McGinnis',
        age: 25,
        posts: {
            post1: true,
        }
    }
},
posts: {
    post1:{
        title: 'What is a jQuery',
        date: 1461131626103,
    }
},
replies: {
    post1: {
        reply1: {
            name: 'Jake Lingwall',
            comment: 'Its a monad',
            id: 'jakelingwall'
        },
        reply2: {
            name: 'Ean Platter',
            comment: 'Its a type of Java',
            id: 'eanplatter'
        }
    }
},
likes: {
    post1: {
        'jakelingwall': true,
        'eanplatter': true,
        'mikenzi': true
    }
}

• 最後列出一個折衷方案

users: {
    tylermcginis: {
        name: 'Tyler McGinnis',
        age: 25,
        posts: {
            post1: true,
        }
    }
},
posts: {
    post1:{
        title: 'What is a jQuery',
        date: 1461131626103,
        likes: {
            'jakelingwall': true,
            'eanplatter': true,
            'mikenzi': true
        },
        replies: {
            post1: {
                reply1: {
                    name: 'Jake Lingwall',
                    comment: 'Its a monad',
                    id: 'jakelingwall'
                },
                reply2: {
                    name: 'Ean Platter',
                    comment: 'Its a type of Java',
                    id: 'eanplatter'
                }
            }
        },
    }
}

• 這些trade-off的取捨，取決於你的AP的需要，根據你的需要來建構最佳的格式