Question

我需要从我的模型中加载来自DB的行，我看过一个教程，但是我在转换类型时遇到错误这是我的模型代码：

public class Question
{
    public Question() {
        Answers = new List<Answer>();
    }

    public int Id { get; set;}
    public string Text { get; set; }
    public List<Answer> Answers { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
    public Boolean Active { get; set; }
public ActionResult Questions()
{
    String connectionString = "Password=********;Persist Security Info=True;User ID=sa;Initial Catalog=PoolMananger;Data Source=.;MultipleActiveResultSets=true";
    String sql = "SELECT * FROM Questions";
    SqlCommand cmd = new SqlCommand(sql, conn);

    var model = new List<Question>();
    using (SqlConnection conn = new SqlConnection(connectionString))
    {
        conn.Open();
        SqlDataReader rdr = cmd.ExecuteReader();
        while (rdr.Read())
        {
            var Question = new Question();
            Question.Text = (rdr["Text"] as string);
            Question.StartDate = rdr["StartDate"];
            Question.EndDate = rdr["EndDate"];
            Question.Active = rdr["Active"];

        model.Add(Question);
        }

    }

    return View(model);
}
}

我在“SqlCommand cmd = new SqlCommand(sql, conn);”上收到错误，错误在“conn”中。也在“return View(model);

上

Answer 1

# Load dataset
smartphone = pd.read_csv('all-users_w4_filtered.csv')

# Define Independent variable (X) and Dependent variable (Y)  
x=smartphone[['mood_mean', 'valence_mean', 'app.social_mean', 'app.other_mean']].values
y=smartphone['target'].values
z=smartphone['benchmark'].values

# Reshape data
x = x.reshape(-1, 4)
y = y.reshape(-1, 1)

# First shuffle the data, then perform k-fold cross-validation
kf = KFold(n_splits=5, shuffle=True, random_state=0)
scores = cross_val_score(regr, x, y, cv=kf)
print ('5-fold shuffled cross validation scores: ', scores)
print ('Mean of cross-validation:', scores.mean())

for train_index, test_index in kf.split(x):
   #print("TRAIN:", train_index, "TEST:", test_index)
   X_train, X_test = x[train_index], x[test_index]
   y_train, y_test = y[train_index], y[test_index]

此时您的SqlCommand cmd = new SqlCommand(sql, conn);尚未存在。因此，在定义它的conn内移动此行。

我认为其他错误发生在

using

将强制转换添加到正确的类型：

Question.StartDate = rdr["StartDate"];

（当然，与其他行做类似的事情）

Answer 2

在将它们分配给类变量之前，您必须转换它们（从服务器返回）。试试这个。

Question.StartDate = Convert.ToDateTime(rdr["StartDate"]);
Question.EndDate = Convert.ToDateTime(rdr["EndDate"]);
Question.Active = Convert.ToBoolean(rdr["Active"]);

请注意，这不会检查任何空值，并假设您没有从服务器返回空值。

Answer 3

我发现你的代码中存在几个问题。

您需要在连接对象可用后创建命令对象
Reader返回Object类型。您需要根据数据库中定义的类型正确键入。我正确更新了你的代码。试试下面。希望这有助于

公共课问题 { 公共问题（） { 答案=新的List（）; }

public int Id { get; set; }
public string Text { get; set; }
public List<Answer> Answers { get; set; }
public DateTime StartDate { get; set; }
public DateTime EndDate { get; set; }
public Boolean Active { get; set; }

public ActionResult Questions()
{
    String connectionString =
        "Password=********;Persist Security Info=True;User ID=sa;Initial Catalog=PoolMananger;Data Source=.;MultipleActiveResultSets=true";

    String sql = "SELECT * FROM Questions";


    var model = new List<Question>();
    using (SqlConnection conn = new SqlConnection(connectionString))
    {
        conn.Open();
        SqlCommand cmd = new SqlCommand(sql, conn);
        SqlDataReader rdr = cmd.ExecuteReader();
        while (rdr.Read())
        {
            var Question = new Question();
            Question.Text = rdr["Text"].ToString();
            Question.StartDate = (DateTime) rdr["StartDate"];
            Question.EndDate = (DateTime) rdr["EndDate"];
            Question.Active = (Booolean) rdr["Active"];

            model.Add(Question);
        }
    }

    return View(model);
}
}

asp.net错误：无法将类型'object'隐式转换为'System.DateTime / Boolean'。存在显式转换（您是否错过了演员？）

3 个答案: