CS0266：无法将类型'object'隐式转换为'System.Data.SqlClient.SqlDataReader'。这个错误导致行dr = cmd.executescalar（） [英] CS0266: Cannot implicitly convert type 'object' to 'System.Data.SqlClient.SqlDataReader'. this error conduct the line dr=cmd.executescalar()

问题描述

public int membercount(string tbl, string condition)
    {
        string query = null;
        if (condition.Trim().Length > 0) 
        {
            query = query + "where" + condition;
        }
        else
        {
            query = query;
        }
        cmd = new SqlCommand(query, con);
       dr= cmd.ExecuteScalar();
        return a;   
    }

推荐答案

正如我在代码块中看到的那样， dr是SqlDataReader 对象。 cmd.ExecuteScalar（） [ ^ ]返回第一个查询返回的结果集中第一行的列。其他列或行将被忽略。



此外，我还可以看到代码中还有一个问题，即您的SQL查询错误。我在这里修改查询。您可以查看一次。

试试这个：

As I can see in your code block, dr is SqlDataReader object. Where as cmd.ExecuteScalar()[^] returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

Additionally, I can see one more problem in your code is, your SQL query is wrong. I am modifying the query here. You can check it once.
Try this:

public int membercount(string tbl, string condition)
{
    string query = "SELECT COUNT(*) FROM " + tbl; //Since your function is for counting member.
    if (condition.Trim().Length > 0)
    {
        query = query + " where " + condition;
    }
    cmd = new SqlCommand(query, con);
    int a = Convert.ToInt32(cmd.ExecuteScalar());//Converting the returned value to Int32
    return a;
}

- Amit

实际上Executescaler（）方法返回



查询返回的结果集中第一行的第一列。额外的列或行将被忽略。



但你已将其分配给博士。这就是为什么你会收到这个错误。

Actually the Executescaler() method returns

the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

but u have assigned it to the dr .Thats why u are getting this error.

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