從SQL數據庫中刪除ListView中的選定項

Question

我試圖創建一種從數據庫表mrydenEntities()中刪除我選擇的項（從列表視圖中刪除）的方法，並使用EntityFramework和Database First模型設置了數據庫。

我收到這個錯誤

System.InvalidOperationException：序列不包含任何元素

我可以肯定地說這意味着我的代碼recipeToRemove = context.Recipe.First(r => r.Id.Equals(Id)); 沒有得到任何相等的比賽。

我不確定我做錯了什么，我在選票上用盡了如何前進。

我的Db類：

public class Dbconnection : INotifyPropertyChanged
    {

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

        public string RecipeName { get; set; }
        public string RecipeIngredients { get; set; }
        public string CookingTime { get; set; }
        public int Id { get; set; }

        mrydendbEntities context = new mrydendbEntities();
        public Recipe recipeToRemove;
        public Recipe Table { get; set; }         

        public void DbconnectionRemove(string RecipeName, string Ingredients, string CookingTime, int Id)
        {
            recipeToRemove = context.Recipe.First(r => r.Id.Equals(Id)); //This is giving me an error System.InvalidOperationException: Sequence contains no elements
            context.Recipe.Remove(recipeToRemove);
            context.SaveChanges();
            MessageBox.Show(recipeToRemove.RecipeName);
        }
    }

我的代碼背后：

public partial class ViewAll : Page, INotifyPropertyChanged
    {
        public int Id { get; set; }

        public string RecipeName { get; set; }

        public string Ingredients { get; set; }

        public string CookingTime { get; set; }

        private Recipe _recipe;
        public Recipe Recipe
        {
            get { return _recipe; }
            set
            {
                if(_recipe != value)
                {
                    _recipe = value;
                    OnPropertyChanged("Recipe");
                }
            }
        }

        public ViewAll()
        {
            InitializeComponent();
            LoadItemTemplate();
        }

        public void LoadItemTemplate()
        {
            mrydendbEntities dbe = new mrydendbEntities();
            listOfRecipes.ItemsSource = dbe.Recipe.ToList();
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        private void Button_Click(object sender, RoutedEventArgs e) //My button event to remove the selected table row.
        {
            var remove = new Dbconnection();
            remove.DbconnectionRemove(RecipeName, Ingredients, CookingTime, Id);
        }

我的mrydendbEntities類：

using System;
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;

    public partial class mrydendbEntities : DbContext
    {
        public mrydendbEntities()
            : base("name=mrydendbEntities")
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }

        public virtual DbSet<Recipe> Recipe { get; set; }
    }

編輯：更改了recipeToRemove = context.Recipe.First(r => r.Id.Equals(Id)); 替換為recipeToRemove = context.Recipe.FirstOrDefault(r => r.RecipeName.Equals(RecipeName)); 這在行context.Recipe.Remove(recipeToRemove);給了我一個新的錯誤消息context.Recipe.Remove(recipeToRemove);

System.ArgumentNullException“值不能為空”

Answer 1

代替這個：

recipeToRemove = context.Recipe.First(r => r.Id.Equals(Id)); //This is giving me an error System.InvalidOperationException: Sequence contains no elements

做這個：

recipeToRemove = context.Recipe.FirstOrDefault(r => r.Id.Equals(Id));

然后在繼續之前檢查結果是否為<null> 。

如果沒有結果，則First將出錯，但是如果沒有結果，則FirstOrDefault將返回<null> 。

Answer 2

我解決了

我必須將recipeToRemove = context.Recipe.FirstOrDefault(r => r.RecipeName.Equals(RecipeName))更改為recipeToRemove = context.Recipe.First(r => r.RecipeName.Equals(r.RecipeName));