今天繼續聊一個最近測試 LiteDB 遇到一個很有趣也很方便的東西， LiteDB 雖然主要是 NoSQL 但是
他也有可以支持類似關聯式資料庫 的操作，畢竟透過正規化資料庫，對於資料規劃也會比較符合主流邏輯
這篇就來聊在 LiteDB 如何做到兩張表( collection ) 的關聯
先說案例說明，有兩個 collection 一個是 ORDERS 負責放訂單資料，一個是 CUSTOMER 負責放客戶資料
所以在每一個 Order 物件中有一個屬性，原本在一般資料庫中，你可以會設計一個 CustomerId 去 relation 到 CUSTOMER 去可以撈取用戶的資料
這裡面，我在 Order 這物件中設計一個 為 Customer 物件型別的屬性為 CustomerData
Data Model:
之後我們先建立兩筆客戶資料到 CUSTOMER
code:
資料結果:
再來我們建立 Order 這邊順便測試一些其他功能 BsonMapper.Global 中你可以設定 把某個 Property 存入資料庫中的時候是使用什麼欄位
也可以忽略某一個不存，有一個很特別的功能就是 DbRef 他就是敘述該物件中哪一個屬性對應到哪一張表並且使用該 ID 進行 MAPPING
寫入後 資料庫內容長這樣
這時候我們把資料庫撈出來看，這邊不要忘記 Query 後面要去加入 Include 該屬性
Result:
{"OrderId":"order1-1","Title":"ORDER-Friend1-1","CreateDate":"2024-02-02T15:59:19.666+08:00","Memo":null,"UserId":"friend1","CustomerData":{"_id":"CUSTOMER1","Name":"CUST1"}}
{"OrderId":"order1-2","Title":"ORDER-Friend1-2","CreateDate":"2024-02-02T15:59:19.674+08:00","Memo":null,"UserId":"friend1","CustomerData":{"_id":"CUSTOMER1","Name":"CUST1"}}
{"OrderId":"order1-3","Title":"ORDER-Friend1-3","CreateDate":"2024-02-02T15:59:19.674+08:00","Memo":null,"UserId":"friend1","CustomerData":{"_id":"CUSTOMER1","Name":"CUST1"}}
{"OrderId":"order1-4","Title":"ORDER-Friend1-4","CreateDate":"2024-02-02T15:59:19.674+08:00","Memo":null,"UserId":"friend1","CustomerData":{"_id":"CUSTOMER1","Name":"CUST1"}}
{"OrderId":"order1-5","Title":"ORDER-Friend1-5","CreateDate":"2024-02-02T15:59:19.675+08:00","Memo":null,"UserId":"friend1","CustomerData":{"_id":"CUSTOMER1","Name":"CUST1"}}
{"OrderId":"order2-1","Title":"ORDER-Friend2-1","CreateDate":"2024-02-02T15:59:19.675+08:00","Memo":null,"UserId":"friend2","CustomerData":{"_id":"CUSTOMER2","Name":"CUST2"}}
{"OrderId":"order2-2","Title":"ORDER-Friend2-2","CreateDate":"2024-02-02T15:59:19.675+08:00","Memo":null,"UserId":"friend2","CustomerData":{"_id":"CUSTOMER2","Name":"CUST2"}}
{"OrderId":"order2-3","Title":"ORDER-Friend2-3","CreateDate":"2024-02-02T15:59:19.676+08:00","Memo":null,"UserId":"friend2","CustomerData":{"_id":"CUSTOMER2","Name":"CUST2"}}
{"OrderId":"order2-4","Title":"ORDER-Friend2-4","CreateDate":"2024-02-02T15:59:19.677+08:00","Memo":null,"UserId":"friend2","CustomerData":{"_id":"CUSTOMER2","Name":"CUST2"}}
{"OrderId":"order2-5","Title":"ORDER-Friend2-5","CreateDate":"2024-02-02T15:59:19.678+08:00","Memo":null,"UserId":"friend2","CustomerData":{"_id":"CUSTOMER2","Name":"CUST2"}}
這時候 CustomerData 就會根據 CUSTOMER 那張表的資料還原回該物件
這設計我覺得很好寫起來很舒服推薦給大家