Xamarin.Forms SQLite exception - 不知道 PartsManagement.Models.Part[] (< - 一个自定义类)

Question

我很抱歉重新发布一个问题，但原文从未以我能理解和利用的方式得到回答。我不确定我是否应该尝试恢复这个问题或产生一个新问题。

我正在尝试将 Part 对象添加到我创建的数据库中的 Part 表中。 我在执行过程中收到以下错误

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:Users5w3rv0sourcereposPartsManagementPartsManagementPartsManagementDatabase.cs:18 
at PartsManagement.App.get_Database () [0x0000e] in C:Users5w3rv0sourcereposPartsManagementPartsManagementPartsManagementApp.xaml.cs:20 
at PartsManagement.Views.NewPartPage.Save_Clicked (System.Object sender, System.EventArgs e) [0x00057] in C:Users5w3rv0sourcereposPartsManagementPartsManagementPartsManagementViewsNewPartPage.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)

从错误消息中，我确定该错误似乎发生在执行第 25 行

期间

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();
}
}
}

下面是部件类：

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，但是我已经使用使用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 对象作为数组查找的特定实例化？ 我已经查看了 sqlite 关键字，但部分似乎不包含在其中。 我的文件夹结构是否对我正在寻找的功能有影响？ 我已经在本地数据库教程中执行了此功能，但此示例的不同之处在于我尝试使用不同的文件夹结构。 不确定这会如何影响，但以防万一我提出来。
此示例文件夹结构

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;
}
}

包括产品类，因为它是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

它在创建Product表时失败，因为SQLite不了解如何创建Part数组。如果要具有 FK 关系的表，则需要添加 SQLite 扩展包