Xamarin.Forms SQLite 异常 - 不知道 PartsManagement.Models.Part[]（<- 自定义 class）

Question

对于这个重新post 的问题，我感到抱歉，但是 original 从来没有以我可以理解和利用的方式回答。我不确定我是应该尝试重新提出这个问题还是产生一个新问题。

我试图在我创建的数据库中向我的零件 table 添加一个零件对象。我在执行期间收到以下错误

System.AggregateException
      Message=One or more errors occurred. (Don't know about PartsManagement.Models.Part[])
      Source=mscorlib
      StackTrace:
      at System.Threading.Tasks.Task.ThrowIfExceptional (System.Boolean includeTaskCanceledExceptions) [0x00011] in /Users/builder/jenkins/workspace/archive-mono/2019-10/android/release/external/corert/src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:2027 
      at System.Threading.Tasks.Task.Wait (System.Int32 millisecondsTimeout, System.Threading.CancellationToken cancellationToken) [0x00043] in /Users/builder/jenkins/workspace/archive-mono/2019-10/android/release/external/corert/src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:2759 
      at System.Threading.Tasks.Task.Wait () [0x00000] in /Users/builder/jenkins/workspace/archive-mono/2019-10/android/release/external/corert/src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:2625 
      at PartsManagement.Database..ctor (System.String dbPath) [0x00027] in C:\Usersw3rv0\source\repos\PartsManagement\PartsManagement\PartsManagement\Database.cs:18 
      at PartsManagement.App.get_Database () [0x0000e] in C:\Usersw3rv0\source\repos\PartsManagement\PartsManagement\PartsManagement\App.xaml.cs:20 
      at PartsManagement.Views.NewPartPage.Save_Clicked (System.Object sender, System.EventArgs e) [0x00057] in C:\Usersw3rv0\source\repos\PartsManagement\PartsManagement\PartsManagement\Views\NewPartPage.xaml.cs:25 
      at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__7_0 (System.Object state) [0x00000] in /Users/builder/jenkins/workspace/archive-mono/2019-10/android/release/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:1021 
      at Android.App.SyncContext+<>c__DisplayClass2_0.<Post>b__0 () [0x00000] in <4ccdb3137d974856b786e1aeebbfbab6>:0 
      at Java.Lang.Thread+RunnableImplementor.Run () [0x00008] in <4ccdb3137d974856b786e1aeebbfbab6>:0 
      at Java.Lang.IRunnableInvoker.n_Run (System.IntPtr jnienv, System.IntPtr native__this) [0x00009] in <4ccdb3137d974856b786e1aeebbfbab6>:0 
      at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.71(intptr,intptr)

根据错误消息，我确定错误出现在第 25 行的执行过程中

await App.Database.SavePartAsync(new Part
            {
                Name = partName.Text,
                Description = partDescription.Text
            });

在 NewPartsPage.xaml.cs 文件中：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

using PartsManagement.Models;

namespace PartsManagement.Views
{
    // Learn more about making custom code visible in the Xamarin.Forms previewer
    // by visiting https://aka.ms/xamarinforms-previewer
    [DesignTimeVisible(false)]
    public partial class NewPartPage : ContentPage
    {
        public NewPartPage()
        {
            InitializeComponent();
        }

        async void Save_Clicked(object sender, EventArgs e)
        {
            if (!string.IsNullOrWhiteSpace(partName.Text) && !string.IsNullOrWhiteSpace(partDescription.Text))
            {
                await App.Database.SavePartAsync(new Part
                {
                    Name = partName.Text,
                    Description = partDescription.Text
                });
            }
            await Navigation.PopModalAsync();
        }

        async void Cancel_Clicked(object sender, EventArgs e)
        {
            await Navigation.PopModalAsync();
        }
    }
}

这是第 class 部分：

using SQLite;

namespace PartsManagement.Models
{
    public class Part
    {
        [PrimaryKey, AutoIncrement]
        public int Id { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
    }
}

和数据库文件：

using System.Collections.Generic;
using System.Threading.Tasks;
using SQLite;

using PartsManagement.Models;

namespace PartsManagement
{
    public class Database
    {
        readonly SQLiteAsyncConnection _database;

        public Database(string dbPath)
        {
            _database = new SQLiteAsyncConnection(dbPath);
            _database.CreateTableAsync<Part>().Wait();
            _database.CreateTableAsync<Product>().Wait();
        }

        public Task<List<Part>> GetPartsAsync()
        {
            return _database.Table<Part>().ToListAsync();
        }

        public Task<int> SavePartAsync(Part aPart)
        {
            return _database.InsertAsync(aPart);
        }

        public Task<List<Product>> GetProductsAsync()
        {
            return _database.Table<Product>().ToListAsync();
        }

        public Task<int> SaveProductAsync(Part aProduct)
        {
            return _database.InsertAsync(aProduct);
        }
    }
}

该错误似乎进一步表明 NewPartsPage 找不到 Part 对象，但我已使用 using PartsManagement.Model; 的正确使用语句引用了它。我不确定错误中的方括号是否重要。它是否试图将 Parts 对象的特定实例化为数组？我已查看 sqlite key words, but Part does not seem to be included in it. Is my folder structure having an impact on the functionality I am looking for? I have performed this functionality in the local database tutorial，但此示例的不同之处在于我尝试使用不同的文件夹结构。不确定这会产生怎样的影响，但以防万一我提出来。
This examples folder structure

    static Database database;

    public static Database Database
    {
        get
        {
            if (database == null)
            {
                database = new Database(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "Inventory.db3"));
            }
            return database;
        }
    }

包括产品 class，因为它是解决此问题根本原因的关键。

using SQLite;

namespace PartsManagement.Models
{
    public class Product
    {
        [PrimaryKey, AutoIncrement]
        public string ID { get; set; }
        public string Name { get; set; }
        public int Cost { get; set; }
        public int OnHand { get; set; }
        public int UsedIn { get; set; }
        public double AveragePerProduct { get; set; }
        public int NumberSold { get; set; }
        public double Price { get; set; }
        public Part[] PartsIn { get; set; }
    }
}

Answer 1

创建 Product table 时失败，因为 sqlite 不理解如何创建 Part 数组。如果你想要 tables 与 FK 关系，你需要添加 SQLite Extensions 包

Xamarin.Forms SQLite 异常 - 不知道 PartsManagement.Models.Part[]（<- 自定义 class）

Xamarin.Forms SQLite exception - don't know about PartsManagement.Models.Part[] (<- a custom class)

sqlite

xamarin

xamarin.forms

sqlite-net-pcl