如何在c#中使用带有参数化查询的SqlDataReader？

Question

我正在查看参数化查询问题,我找不到使用SqlDataReader参数化查询来填充下拉列表的示例.

现在,我可以在这里使用我的代码填充我的下拉

if (!this.IsPostBack)
{
    using (SqlConnection con = new SqlConnection(SQLConnectionString))
    {
        System.Data.SqlClient.SqlCommand go = new System.Data.SqlClient.SqlCommand();

        con.Open();
        go.Connection = con;
        go.CommandText = "SELECT InsuredID, FirstName, LastName FROM [Lab2].[dbo].[INSURED]";
        go.ExecuteNonQuery();

        SqlDataReader readIn = go.ExecuteReader();

        while (readIn.Read())
        {
            ddlHomeInsuredID.Items.Add(
                new ListItem(readIn["InsuredID"].ToString() + " : " + readIn["FirstName"].ToString()
                + " " + readIn["LastName"].ToString()));
        }

        con.Close();

        ddlHomeInsuredID.Items.Insert(0, new ListItem("--Select InsuredID--", "0"));
    }
}

但是,我想让这个select语句参数化.我怎样才能做到这一点？我很乐意编写参数化的插入语句,如下所示:

using (SqlConnection connection = new SqlConnection(SQLConnectionString))
{
    SqlCommand command = new SqlCommand();
    command.Connection = connection;
    command.CommandType = System.Data.CommandType.Text;

    command.CommandText = @"INSERT INTO [Lab2].[dbo].[INSURED] ([FirstName], [LastName], [MI], [DateOfBirth], 
[CreditScore], [AddressID], [DriversLicenseNumber], [LastUpdatedBy], [LastUpdated]) VALUES
(@firstName, @lastName, @middleInitial, @dateOfBirth, @creditScore, @addressID,
@driversLicenseNumber, @lastUpdatedBy, @lastUpdated)";

    command.Parameters.Add("@firstName", SqlDbType.VarChar, 20).Value = Insured.insuredArr[j].getFirstName();
    command.Parameters.Add("@lastName", SqlDbType.VarChar, 30).Value = Insured.insuredArr[j].getLastName();
    command.Parameters.Add("@middleInitial", SqlDbType.Char, 1).Value = Insured.insuredArr[j].getMiddleInitial();
    command.Parameters.Add("@dateOfBirth", SqlDbType.VarChar, 30).Value = Insured.insuredArr[j].getDateOfBirth();
    command.Parameters.Add("@creditScore", SqlDbType.Int).Value = Insured.insuredArr[j].getCreditScore();
    command.Parameters.Add("@addressID", SqlDbType.Int).Value = Insured.insuredArr[j].getAddressID();
    command.Parameters.Add("@driversLicenseNumber", SqlDbType.VarChar, 30).Value = Insured.insuredArr[j].getDriversLicenseNumber();
    command.Parameters.Add("@lastUpdatedBy", SqlDbType.VarChar, 20).Value = Insured.insuredArr[j].getLastUpdatedBy();
    command.Parameters.Add("@lastUpdated", SqlDbType.Date).Value = Insured.insuredArr[j].getLastUpdated();

    connection.Open();
    command.ExecuteNonQuery();
    connection.Close();
}

MsgBox("Record(s) inserted into database", this.Page, this);

那么,我怎样才能像第二个例子那样进行第一次查询？

谢谢

nammrick

Answer 1

首先,ExecuteNonQuery()方法的使用对SELECT查询无效,ExecuteReader()因为你想要返回查询结果.这是ExecuteNonQuery方法的用法说明:

您可以使用ExecuteNonQuery执行目录操作(例如,查询数据库的结构或创建数据库对象,例如表),或者通过执行UPDATE,INSERT或DELETE语句来更改数据库中的数据而不使用DataSet .

修改后的查询流应该是这样的:

using (SqlConnection con = new SqlConnection(SQLConnectionString))
{
    SqlCommand go = new SqlCommand();

    con.Open();
    go.Connection = con;
    go.CommandText = "SELECT InsuredID, FirstName, LastName FROM [Lab2].[dbo].[INSURED]";

    SqlDataReader readIn = go.ExecuteReader();
    while (readIn.Read())
    {
       // reading data from reader
    }

    con.Close();

    // other stuff
}

如果要对SELECT语句使用参数化查询,则需要在WHERE子句中包含至少一个列(和一个参数名称)(请参见下面的示例):

SELECT InsuredID, FirstName, LastName FROM [Lab2].[dbo].[INSURED] WHERE InsuredID = @InsuredID

然后,您可以使用SqlParameter将参数值传递到上面的查询中:

using (SqlConnection con = new SqlConnection(SQLConnectionString))
{
    System.Data.SqlClient.SqlCommand go = new System.Data.SqlClient.SqlCommand();

    con.Open();
    go.Connection = con;
    go.CommandText = "SELECT InsuredID, FirstName, LastName FROM [Lab2].[dbo].[INSURED] WHERE InsuredID = @InsuredID";
    go.Parameters.Add("@InsuredID", SqlDbType.Int).Value = 1; // example value for parameter passing

    SqlDataReader readIn = go.ExecuteReader();
    while (readIn.Read())
    {
       // reading data from reader
    }

    con.Close();

    // other stuff
}

注意:避免INSERT/UPDATE/DELETE在SELECT使用相同活动连接的语句填充数据的同时执行操作,应在执行另一个查询之前先关闭先前的连接.

更多例子:

如何在sql语句中使用字符串变量

如何使用sql参数进行选择查询？