Question

我试图用Visual Studio创建一个localdb。我使用c＃连接和插入新行。我不了解问题是在Visual Studio服务器资源管理器数据库连接中还是在我的代码中。

要将行插入数据库，我从[Using SqlDataAdapter to insert a row 。当用户单击按钮时，此连接应正常工作，但调试时出现空引用异常

import java.time.LocalDate;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

public class Conteudo {

    private final ObjectProperty<LocalDate> data = new SimpleObjectProperty<>(this, "data",null);
    private final StringProperty aula = new SimpleStringProperty(this, "aula",null);
    private final StringProperty conteudo = new SimpleStringProperty(this, "conteudo", null);

    public Conteudo() { 
        this(null, null, null); // chama outro construtor
    }

    public Conteudo(LocalDate dt, String au, String cont) {
        this.data.set(dt);
        this.aula.set(au);
        this.conteudo.set(cont);
    }

    public void setDate(LocalDate dt) {
        data.set(dt);
    }
    public LocalDate getDate() {
        return data.get();
    }

    public final ObjectProperty<LocalDate> dateProperty() {
        return data;
    }

    public void setAula(String au) {
        this.aula.set(au);
    }
    public String getAula() {
        return aula.get();
    }
    public void setConteudo(String cont) {
        this.conteudo.set(cont);
    }
    public String getConteudo() {
        return conteudo.get();
    }

}

我在Visual Studio中创建了3个localdb，所以只有其中一个已连接。也许我使用的是错误的。如果变量con中有问题，我该怎么理解？为了轻松实现问题，调试时的con值在下面；

SqlConnection con = new SqlConnection(@"Data Source = (LocalDB)\MSSQLLocalDB;AttachDbFilename= C:\somepath.mdf; Integrated Security = True;");
con.Open();
SqlDataAdapter sqlDataAdapter = new SqlDataAdapter("SELECT * FROM mytablename WHERE 0 = 1", con);

DataSet dataSet = new DataSet();
sqlDataAdapter.Fill(dataSet);

DataRow newRow = dataSet.Tables["mytablename"].NewRow();  // null reference exception
newRow["username"] = "un";
newRow["myaccountusername"] = "maun";
dataSet.Tables["mytablename"].Rows.Add(newRow);

new SqlCommandBuilder(sqlDataAdapter);
sqlDataAdapter.Update(dataSet);

localdb创建新行null异常

0 个答案: