检查表，如果在C＃中语句存在？ [英] Check if table exists with if statement in C#?

问题描述

我尽量把了一个，如果检查语句是否已经创建了一个表。我只是想创建一个表，但是因为它是现在我创建一个表我点击按钮存储信息每次。有什么建议么？

I try to put up an if statement to check if a table is already created. I only want to create one table, but as it is now I create a table every time I click the button to store the info. Any suggestions?

    DataTable dt;

    private void InitDataTable()
    {

        if () { 

        }

        dt = new DataTable();
        DataSet ds = new DataSet();
        ds.ReadXml("gjesteInfo.xml");
        ds.Tables.Add(dt);

        DataColumn dc1 = new DataColumn("Fullt navn");
        DataColumn dc2 = new DataColumn("Start dato");
        DataColumn dc3 = new DataColumn("Antall dager");

        dt.Columns.Add(dc1);
        dt.Columns.Add(dc2);
        dt.Columns.Add(dc3);

        dt.Rows.Add(gjestenavnInput.Text, datoInnsjekk.Text, antallDager.Text);

        ds.Merge(dt);

        ds.WriteXml("gjesteInfo.xml");

    }



    private void lagre_Click(object sender, EventArgs e)
    {

        InitDataTable();

        gjesterutenrom.Items.Add(gjestenavnInput.Text);

        gjestenavnInput.Text = "";
        datoInnsjekk.Text = "";
        antallDager.Text = "";

        DataSet onClick = new DataSet();
        onClick.ReadXml("gjesteInfo.xml");
        lagredeGjester.DataSource = onClick.Tables[0];

    }

我试图让出存储在XLM的信息。一个名为lagredeGjester因为看到了DataGridView的

I try to get out the info stored in the XLM with a DataGridView named lagredeGjester as seen over.

已更新问题：

现在我写这样的代码：

    DataTable dt;

    DataSet ds = new DataSet();

    private void InitDataTable()
    {


         if( ds.Tables.Contains("Gjester")   )
        {
            dt.Rows.Add(gjestenavnInput.Text, datoInnsjekk.Text, antallDager.Text);
            ds.Merge(dt);

            ds.WriteXml("gjesteInfo.xml");

        }
        else {

            dt = new DataTable("Gjester");

            ds.ReadXml("gjesteInfo.xml");
            ds.Tables.Add(dt);

            DataColumn dc1 = new DataColumn("Fullt navn");
            DataColumn dc2 = new DataColumn("Start dato");
            DataColumn dc3 = new DataColumn("Antall dager");

            dt.Columns.Add(dc1);
            dt.Columns.Add(dc2);
            dt.Columns.Add(dc3);

            dt.Rows.Add(gjestenavnInput.Text, datoInnsjekk.Text, antallDager.Text);
            ds.Merge(dt);

            ds.WriteXml("gjesteInfo.xml");

        }

    }

在我的第一个跑我进入两个不同的infomations和我按下按钮。无论信息在同一个表作为了我想它。但我似乎无法正确地写我的if语句。当我运行上面的代码将其与一个空的XML工作（无表），但只要Gjester表创建它说的DataTable名为Gjester'已经属于此DataSet。但是，这不就是if语句应该避免什么我？正如我现在写的，应该把它不只是添加信息，不要试图创建新表？

On my first run I entered two different infomations and pressed my button. Both info got in the same table as I wanted it to. But I can't seem to write my if statement correctly. When I run the code above it works with an empty XML (with no tables), but as long as "Gjester" table is created it says "A DataTable named 'Gjester' already belongs to this DataSet." But isn't this what my if statement should prevent? As I wrote it now, should it not just add the info and not try to create a new table?

推荐答案

可以检查通过

if(ds.Tables.Contains("tablename"))

或

 if(dt.Rows.Count == 0)

或

int flag=0;
try
{

    if(ds.Tables["tablename"].Rows.Count>0)
    {
      // execute something
    }
}
catch(Exception ex)
{
 flag=1;
}

if(flag==1)
{
  messagebox.show("Table does not exists");
}

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