DataTable属性 - NullReferenceException

Question

我正在编写一个从数据库导入数据的程序。我想把所有这些表放在我自己的对象中。所有这些DataTable属性都被填充，直到执行Base examBase = Base()，但在此行之后，exam.Base.Tests不再存在。是什么原因造成的？

class Base
{
    MySqlConnection myConnection;
    MySqlDataAdapter testsDataAdapter;
    DataTable testsDataTable;
    MySqlDataAdapter questionsDataAdapter;
    DataTable questionsDataTable;
    MySqlDataAdapter answersDataAdapter;
    DataTable answersDataTable;



    public Base()
    {
        string myConnectionString = "Database=Exams;Data Source=localhost;User Id=root;Password=";
        myConnection = new MySqlConnection(myConnectionString);
        myConnection.Open();
        GetTests();
        GetQuestions();
        GetAnswers();
    }

    private void GetTests()
    {
        string testQuery = "SELECT * FROM tests";
        testsDataAdapter = new MySqlDataAdapter(testQuery, myConnection);
        testsDataTable = new DataTable();
        testsDataAdapter.Fill(testsDataTable);
        testsDataTable.PrimaryKey = new DataColumn[] { testsDataTable.Columns["TestID"] };

        this.Tests = testsDataTable;
    }

    private void GetQuestions()
    {
        string questionQuery = "SELECT * FROM questions";
        questionsDataAdapter = new MySqlDataAdapter(questionQuery, myConnection);
        questionsDataTable = new DataTable();
        questionsDataAdapter.Fill(questionsDataTable);

        this.Questions = questionsDataTable;
    }

    private void GetAnswers()
    {
        string answerQuery = "SELECT * FROM answers";
        answersDataAdapter = new MySqlDataAdapter(answerQuery, myConnection);
        answersDataTable = new DataTable();
        answersDataAdapter.Fill(answersDataTable);

        this.Answers = answersDataTable;
    }
    public DataTable Tests { get; set; }
    public DataTable Questions { get; set; }
    public DataTable Answers { get; set; }


}

首先在GetName（）方法中看到异常：

 class Test
{
    Base examBase;
    private List<Question> questions;

    public Test(int testID)
    {
        examBase = new Base();
        this.TestID = testID;

        GetName();
        GetDescription();
        GetAuthor();
        GetQuestions();

    }

    private void GetName()
    {

        this.Name = examBase.Tests.Rows.Find(this.TestID)["Name"].ToString();

    }

修改

好的，对象examBase.Tests存在，但是有一些使用whis Find()方法的东西。在我的基础上，在表格中＆＃34;测试＆＃34;我有一个主键（列TestID），但我得到了KeyMissing异常。 Meybe我错误地使用了这个Find()？