Cannot implicitly convert type 'System.Data.Common.DbDat

本文关键字：System Data Common DbDat implicitly convert type Cannot | 更新日期: 2023-09-27 18:01:34

我一直得到一个错误的阅读器。我只希望能够从阅读器返回单个值。有人能帮帮我吗?

        DbProviderFactory factory = DbProviderFactories.GetFactory("System.Data.SqlClient");
        DbConnection conn = factory.CreateConnection();
        conn.ConnectionString = ConfigurationManager.ConnectionStrings["CompanyConnection"].ConnectionString;
        DbCommand comm = conn.CreateCommand();
        comm.CommandText = "getStockPrice";
        comm.CommandType = CommandType.StoredProcedure;
        DbParameter param = comm.CreateParameter();
        param.ParameterName = "@company";
        param.Value = CompanyName;
        param.DbType = DbType.String;
        comm.Parameters.Add(param);
        conn.Open();
        DbDataReader reader = comm.ExecuteReader();
        string stock = reader;
        reader.Close();
        conn.Close();
        return Convert.ToDouble(stock);

这是存储过程:

        @company varchar(50)
    AS
Select stockPrice From Company_t
where companyName = @company;

Cannot implicitly convert type 'System.Data.Common.DbDat

您必须这样做:

string stock = reader.GetString(0);

或

string stock = reader.GetString(reader.GetOrdinal("stockPrice"));
不是

string stock = reader;
编辑:

您可以使用GetDouble()代替GetString()，并跳过Convert.ToDouble()

尝试呼叫ExecuteScalar 

string stock = (string)comm.ExecuteScalar();

我觉得你的代码有问题

string stock = reader;

你不能那样做，你必须实际从读取器获取数据。

查看文档获取更多信息

您不能直接访问DataReader中的数据而不读取它。这个方法不会破坏你的代码，即使你的查询没有返回数据。

DbDataReader reader = comm.ExecuteReader();
string stock = "0";
while (reader.Read())
{
    // get the results of each column
    stock = reader["stockprice"].ToString();
    break;
}
reader.Close();
conn.Close();
return Convert.ToDouble(stock);
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