数据库中的更新行

Question

我正在用c＃和ADO .NET实体数据模型开发一个应用程序。我有一个表文章（idArticle，nameArticle，statusArticles）。我想检索statusArticle = false的第一篇文章，并将其值更新为true。有人能帮助我这个代码，请：

private void button_Click(object sender, EventArgs e) 
     { 
      using (DbEntities db = new DbEntities()) 
      { 
       Articles firstArticle = db.Articles.FirstOrDefault(u => u.statusArticle == false); 
       if (firstArticle != null) 
       { 
        firstArticle.statusArticle = true; 
        MessageBox.Show("Article validated", "OK"); 
        this.Refresh(); 
       } 
      } 
     } 

Answer 1

这可以如下

private void button_Click(object sender, EventArgs e) 
    { 
     using (DbEntities db = new DbEntities()) 
     { 
      Articles firstArticle = db.Articles.FirstOrDefault(u => u.statusArticle == false); 
      // firstArticle is not null anyways as you are calling FirstOrDefault() 
     **EDIT** // In case nothing has status = false, you will get a new Articles object, so instead of the below null check, you have to check for other property like id or name that will be unique. 
      if (firstArticle != null) 
      { 
       firstArticle.statusArticle = true; 
       db.SaveChanges(); 
       MessageBox.Show("Article validated", "OK"); 
       this.Refresh(); 
      } 
     } 
    } 

Answer 2

.FirstOrDefault()

public static TSource FirstOrDefault<TSource>(
    this IEnumerable<TSource> source //db.Articles 
) 

将返回：

默认（TSource）如果来源是空的;否则，源中的第一个元素。

默认（TSource）返回null参考型元件或（通常）0值类型的元件。

你修改代码：

private void button_Click(object sender, EventArgs e) 
     { 
      using (DbEntities db = new DbEntities()) 
      { 
       Articles firstArticle = db.Articles.FirstOrDefault(u => u.statusArticle == false); 
       if (firstArticle != null) 
       { 
        firstArticle.statusArticle = true; 
        MessageBox.Show("Article validated", "OK"); 
        db.SaveChanges(); //change (can go before/after validation message) 
        this.Refresh(); 

       } 
      } 
     }