从数据库表中选择信息 [英] Select information from database table

问题描述

您好，我正在使用ADO .NET数据实体模型进行ac＃项目，我有一个表主题列（idSubject（int），nameSubject（nvarchar），subjectNoted（bit / boolean）。我来自表格第一个主题有`subjectNoted == false`然后我点击一个按钮后我将值改为`== true`：

 私有  void  button1_Click（ object  sender，EventArgs e）
 {
 使用（DbEntities db =  new  DbEntities（））
 {
主题firstSubject = db.Subjects.FirstOrDefault（s = >  s.subjectNoted ==  false ）; 
  if （firstSubject！=  null ）
 {
 firstSubject.subjectNoted =  true ; 
 db.SaveChanges（）; 
 MessageBox.Show（ 主题注释， 确定）; 
} 
} 
} 
 
  private   void  button2_Click（ object  sender，EventArgs e）
 {
  //  显示下一个主题的代码：subjectNoted == false  
} 

我有另一个按钮，这个必须忽略第一个主题，并用`subjectNoted == false`显示第二个主题。我创建了一个方法ShowSubject，但我找不到如何选择第二个主题有`subjectNoted == false`并用方法显示它？

  private   void  ShowSubject（主题主题）
 {
  using （DbEntities db =  new  DbEntities（））
 {
 Subjects firstSubject = db.Subjects.FirstOrDefault （s = >  s.subjectNoted ==  false ）; 
  if （firstSubject！=  null ）
 {
 textBox1。 Text = firstSubject.nameSubject; 
} 
} 
} 

有人可以帮助我，我会被困在这里！

解决方案

您是否尝试过使用Skip（）和Take（）方法？



Skip（n）将跳转n条记录和Take（n）将返回许多记录。



例如你可以尝试

  var  subject = db 
 .Subjects 
 .Where（s = >  s.subjectNoted = =  false ）
 .OrderBy（s = >  s.idSubject）
 .Skip（ 1 ）
 .Take（ 1 ）
 .FirstOrDefault（） ; 

有一件事是你需要在查询之前添加订单才能跳过/取走。

private void ShowSubject（Subjects subject）

{

使用（DbEntities db = new DbEntities（））

{

主题firstSubject = db.Subjects.FirstOrDefault（s => s.subjectNoted == false）.Skip（1）.Take（1）.FirstOrDefault（）;

if（firstSubject！= null）

{

textBox1.Text = firstSubject.nameSubject;

}

}

}

Hello, i m doing a c# project with ADO .NET data entity model, i have a table Subjects with columns (idSubject(int), nameSubject(nvarchar), subjectNoted(bit/boolean). I''m getting from the table the first subject that have `subjectNoted==false` then i change the value to `==true` after clickin a button with this code:

private void button1_Click(object sender, EventArgs e)
            {
                using (DbEntities db = new DbEntities())
                {
                Subjects firstSubject = db.Subjects.FirstOrDefault(s => s.subjectNoted == false);
                    if (firstSubject != null)
                    {
                        firstSubject.subjectNoted = true;
                        db.SaveChanges();
                        MessageBox.Show("Subject Noted", "OK");                    
                    }
                }
            }
    
            private void button2_Click(object sender, EventArgs e)
            {
        //code to show the next subject that have subjectNoted==false
            }

I have another button, this one must ignore the first subject and show the second one with `subjectNoted==false`. I created a method ShowSubject, but i can''t find how to select the second subject that have `subjectNoted==false` and show it with the methode??

private void ShowSubject(Subjects subject)
            {
                using (DbEntities db = new DbEntities())
                {
                   Subjects  firstSubject = db.Subjects.FirstOrDefault(s => s.subjectNoted == false);
                    if (firstSubject != null)
                    {
                        textBox1.Text = firstSubject.nameSubject;
                    }
                }
            }

Someone can help me please i''m stuck here!

解决方案

Have you tried using Skip() and Take() methods ?

Skip(n) will jump the n number of records and Take(n) will return n many records.

for example you could try

var subjects = db
    .Subjects
    .Where(s=> s.subjectNoted == false)
    .OrderBy(s=> s.idSubject)
    .Skip(1)
    .Take(1)
    .FirstOrDefault();

One thing is you do need to add an order by to your query before you can do a skip / take.

private void ShowSubject(Subjects subject)
{
using (DbEntities db = new DbEntities())
{
Subjects firstSubject = db.Subjects.FirstOrDefault(s => s.subjectNoted == false).Skip(1).Take(1) .FirstOrDefault();
if (firstSubject != null)
{
textBox1.Text = firstSubject.nameSubject;
}
}
}

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