Question

SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["connecton1"].ConnectionString);
conn.Open();
SqlCommand check = new SqlCommand("SELECT Location FROM Items WHERE Serial="+Convert.ToInt32(Serialtxt.Text).ToString()+"", conn);
string checker = check.ExecuteReader();

我正在尝试在我的数据库中查找一段数据并将其分配给变量。我得到的错误是

无法将类型'System.Data.SqlClient.SqlDataReader'隐式转换为字符串

我做错了什么？

Answer 1

您必须改为使用ExecuteScalar。

string checker = (string)check.ExecuteScalar();

您还应该使用sql-parameters来阻止sql-injection。

SqlCommand check = new SqlCommand("SELECT Location FROM Items WHERE Serial = @Serial", conn);
check.Parameters.AddWithValue("@Serial", Convert.ToInt32(Serialtxt.Text));

如果您希望每个序列有多行，则可以使用ExecuteReader并填写List<string>：

List<string> allLocations = new List<string>();
using(SqlDataReader rd = check.ExecuteReader())
while(rd.Read())
    allLocations.Add(rd.GetString(0));

Answer 2

将检查器类型从string更改为SqlDataReader

然后你可以做

SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["connecton1"].ConnectionString);
conn.Open();
SqlCommand check = new SqlCommand("SELECT Location FROM Items WHERE Serial           ="+Convert.ToInt32(Serialtxt.Text).ToString()+"", conn);
SqlDataReader checker = check.ExecuteReader();

    while (checker.Read())
    {
           if (checker[0] != null)
           {
              //some logic with the result
           }
    }

我的选择陈述有什么问题？

2 个答案: