The nested dataset feature of ClientDataSet is used to solve the Master-Details design pattern in which a TDataSet field is inserted into the column list. This feature has always been considered a magical technique.
However, the core of database technology is still SQL, so let's take a look at how Delphi uses SQL to pull data in the nested dataset mode.
Surprisingly, the way to pull data is to fetch all details to the client-side at once when fetching data from the header.
Recently, EMBT published an interesting article in their official news: "This Is How To Store Cross Platform App Settings In JSON" by the Softacom Information team. This emerging team collects and publishes articles from Delphi enthusiasts worldwide, so it's unclear who the original author is.
The article discusses that in addition to XML (Extensible Markup Language) and
INI (Initial) formats, modern cross-platform applications often use JSON for
configuration files, with Visual Studio Code as a classic example.
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Visual Studio Code Workspace Settings File |
The article pointed out that Delphi provides two JSON libraries: JSON Objects Framework and Readers and Writers JSON Framework. The author also mentioned the most widely used alternative open-source option, X-SuperObject, provided by Turkish engineer Onur YILDIZ. It's interesting to note that the JSON Objects Framework provides JSON Marshaling/Un-Marshaling, so what makes it different from X-SuperObject?
The author complains that Delphi engineers have been spoiled by the official JSON frameworks. Is that true?
The article points out that Delphi provides two JSON libraries: JSON Objects Framework and Readers and Writers JSON Framework. As an alternative, the author suggests using the widely popular open-source variant X-SuperObject by Turkish engineer Onur YILDIZ. Curiously, JSON Objects Framework provides JSON Marshaling/Un-Marshaling, so how does it differ from X-SuperObject?
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | TContact = class(TObject) public Name: string; Age: Integer; function ToString: string; override; end; procedure TForm1.JSONMarshalClick(Sender: TObject); var LContact: TContact; oMarshaller: TJSONMarshal; crtVal: TJSONValue; begin LContact := TContact.Create; //our custom class LContact.Name:='Hello Eden'; LContact.Age := 20; //fill with some data oMarshaller := TJSONMarshal.Create(TJSONConverter.Create); //our engine crtVal := oMarshaller.Marshal(LContact); //serialize to JSON try Memo1.Text := crtVal.ToString; //display finally //cleanup FreeAndNil(LContact); FreeAndNil(oMarshaller); crtVal.Free; end; end; |
1 2 3 4 5 6 7 8 | {
"type": "Unit2.TContact",
"id": 1,
"fields": {
"Name": "Hello Eden",
"Age": 20
}
}
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The JSON format produced by TObject using the JSON Objects Framework (JOF) is not as intuitive as the one produced by X-SuperObject. Users might need some time to learn the JOF format to manage their configurations.
This has to do with the original purpose of JOF. Around 2009, Delphi 2009 made a transition in DataSnap Framework from XML RPC to JSON RPC. As mentioned earlier, JOF was initially created to serve DataSnap, among other things, such as handling Delphi TObject's strong typing. Therefore, the format produced by JOF is not a weakly-typed compatible JSON format.
So, the author's claim that Delphi engineers are spoiled by the two built-in JSON frameworks is not baseless. After getting used to Delphi's native tools, it may be difficult to accept content that deviates from the "Delphi standard."
Knowing that the built-in JOF won't produce a generic JSON format, you can still create your own. Have you heard of TDBXJSONTools? It can be used to convert TDataSet to JSON, so let's add TObject-to-JSON functionality to it!
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TDBXJSONToolsHelper adds ObjToJSON functionality |
The original example is excellent and deserves a 5-star rating. I modified the example into a VCL project and replaced X-SuperObject usage with JOF, such as in the configuration file loading section:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | procedure TMyProgSettings.LoadFromFile(AFileName: string = ''); var LJObj: TJSONObject; begin if AFileName = '' then AFileName := GetDefaultSettingsFilename(); if not FileExists(AFileName) then Exit; LJObj := TJSONObject.Create; try if LJObj.Parse(TFile.ReadAllBytes(AFileName), 0) > 0 then begin // Magic method from Eden's TDBXJSONToolsHelper unit TDBXJSONTools.JsonToObj(LJObj, Self); end; finally LJObj.Free; end; end; |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | procedure TMyProgSettings.SaveToFile(AFileName: string = ''); var Json: string; begin if AFileName = '' then AFileName := GetDefaultSettingsFilename(); // Magic method from Eden's TDBXJSONToolsHelper unit with TDBXJSONTools.ObjToJSON(Self) do begin Json := ToJson; TFile.WriteAllText(AFileName, Json, TEncoding.UTF8); Free; end; end; |
Being "spoiled" by JOF is, in my opinion, a blessing. JOF is a framework well worth learning, and X-SuperObject offers even more features for JSON writing. If you frequently need to write JSON objects, X-SuperObject will definitely win your heart. Additionally, I enjoyed the original author's example of a login process using a while loop to control the login window; it's a great concept to learn.
You can download the TDBXJSONToolsHelper and VCL example program from my Github website: https://github.com/Eden5Wu/HelperClass/tree/master/Demo-JSON/JsonMarshalling
In summary, both the JSON Objects Framework (JOF) and X-SuperObject have their own unique advantages when working with JSON in Delphi. Developers should choose between them based on their specific needs and preferences.
For developers familiar with the Delphi style, JOF provides a familiar environment for working with JSON. However, if you need more control over JSON object writing, then X-SuperObject may be a better choice.
In any case, exploring and learning about the different JSON frameworks available is essential. By understanding their strengths and weaknesses, you can make more informed decisions about which tools to use in your projects.
Remember, practice and experimentation are key to becoming proficient in any programming language or framework. Therefore, don't be afraid to try different approaches and learn from the examples and experiences of other developers in the Delphi community.
最近 EMBT 官方新聞出現我很感興趣的文章：This Is How To Store Cross Platform App Settings In JSON，是由 Softacom Information 團隊執筆，這是一個新興團隊，匯整來自全球各地 Delphi 愛好者的文章並發表，所以還不知道真實原作者是誰。
原文作者說明在跨平台應用程式在讀寫設定檔時，除了 XML (Extensible Markup Language) 和 INI (Initial) 外，還有一個現代化應用程式常使用的設定檔格式：JSON，例如 Visual Studio Code 就是一個經典的參考。
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Visual Studio Code 工作區設定檔 |
原作控訴 Delphi 工程師已經被官方 JSON 框架寵壞了 (笑)，是真的嗎？
在使用 Delphi 或 C++ Builder 時往往會遇到一些操作不習慣、漏洞 (Bugs) 等問題，以前的 Borland, CodeGear 時期就有品質控制 (QC) 網站，但實際使用上不是連不上就是不知道哪一個才是有在維護的連結，所以會很依賴代理商代為傳遞問題回報的工作，回報者很難得到最快最直接的回應。
原本測試環境打算使用 Interbase，想到自己已經有 SQL Server Driver，不拿來用有點可惜。
索性就試著拿 SQL SERVER LocalDB 來試試。
安裝和建立很簡單，到微軟的線上手冊即可下載：
點擊紅框處就可以下載 SQL2019-SSEI-Expr。
C:\Users\Eden>sqllocaldb c
LocalDB instance "MSSQLLocalDB" created with version 15.0.2000.5.
C:\Users\Eden>sqllocaldb start
LocalDB instance "MSSQLLocalDB" started.
C:\Users\Eden>sqllocaldb info "MSSQLLocalDB"
Name: MSSQLLocalDB
Version: 15.0.2000.5
Shared name:
Owner: EDEN-WIN10\Eden
Auto-create: Yes
State: Running
Last start time: 2022/4/10 下午 11:00:17
Instance pipe name: np:\\.\pipe\LOCALDB#<use your pipe name>\tsql\query
*<use your pipe name>在每次啟動時都會不一樣。
之後可以使用 SSMS 以 pipe 提供的內容進行連接；我在這裡使用 sqlcmd 來建立，而 sqlcmd 在安裝前必須先安裝 ODBC 17 for SQL SERVER。
到 github -- instnwnd.sql 下載 SQL 檔，並且更換 mdf / ldf 路徑後 (不換也可以)，執行即可建立南風範例資料庫。
建立方式相當簡單，搞懂一些小細節後，可以很快的把開發環境建構起來。
在本文中，我們介紹了如何安裝和建立 SQL Server 2019 Express LocalDB，以及如何使用 SQLCMD 建立南風資料庫。不過，如果你想進一步了解 LocalDB 的功能和優點，以下是一些相關的資訊：
和你分享。 😘
