xamarin-forms sqlite多张表

Question

不能使用多个表。如何处理两张、三张或更多张桌子？

Visual >>> Xamarin-Forms

/// I think maybe this code needs to be fixed somehow.
/// this code is placed in App.cs (up)
static Data.TableTwo tabletwo;
static Data.TableOne tableone;

/// crashed
 public Task<int> SaveItemAsync(TableTwo item)
        {
            if (item.ID != 0)
            {
                return tabletwo.UpdateAsync(item);
            }
            else
            {
                return tabletwo.InsertAsync(item);
            }
        } 

/// ***I think maybe this code needs to be fixed somehow.
/// this code is placed in App.cs (down below)
public static Data.TableTwo tabletwo
        {
            get
            {
                if (datadistance == null)
                {
                    tabletwo = new Data.TableTwo(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "TodoSQLite.db3"));
                }
                return tabletwo;
            }
        }

/// ***I think maybe this code needs to be fixed somehow.
/// this code is placed in App.cs (down below)
        public static Data.TableOne tableone
        {
            get
            {
                if (tableone == null)
                {
                    tableone = new Data.TableOne(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "TodoSQLite.db3"));
                }
                return tableone;
            }
        }

以上代码工作正常。当上面的代码被调用时。申请失败。

我有两张桌子。在用户工作时，使用一个表(保存和删除数据)，那么所有操作都正常。如果用户开始使用另一个表(保存数据)，应用程序就会崩溃。

应用程序树！DataBase(文件夹)TableTwo(文件)TableOne(文件)模型(文件夹)TableTwo(文件)TableOne(文件)

所有的事情都是按照https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/databases#using-sqlite文章中的代码做的

实际上，我只是第二次复制了代码，然后粘贴到了项目中。-这就是我所做的，创建第二个表并使用它(删除插入数据)

Answer 1

让我们假设您的两个表类型为Load和MyDatabase，数据库的类型为MyDatabase，您可能希望在MyDatabase类中保持到SqlLite的单个连接，并添加与表交互的方法，如下所示：

public class MyDatabase
{
    private readonly SQLiteAsyncConnection _connection;

    public MyDatabase():this(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "MyDatabase.db3"))
    {
    }

    internal MyDatabase(string dbPath)
    {
        _connection = new SQLiteAsyncConnection(dbPath);

        _connection.CreateTableAsync<Load>().Wait();
        _connection.CreateTableAsync<Category>().Wait();
    }

    public Task<List<Load>> GetLoads() => 
        _connection.Table<Load>().ToListAsync();

    public Task<List<Category>> GetCategories() => 
        _connection.Table<Category>().ToListAsync();

    public Task<Load> GetLoad(int id) => 
        _connection.Table<Load>().Where(i => i.Id == id).FirstOrDefaultAsync();

    public Task<int> SaveLoad(Load item) =>
        item.Id != 0 ? _connection.UpdateAsync(item) : _connection.InsertAsync(item);

    public Task<int> DeleteLoad(Load item) => 
        _connection.DeleteAsync(item);
}

下面是一个很好的示例：https://github.com/xamarin/xamarin-forms-samples/blob/master/Todo/Todo/Data/TodoItemDatabase.cs，但是它包含一个表