Question

从组合选择的值中将此值传递到存储过程，并使用序列化生成条形图仪表板。但这向我显示了一个错误

无法将字符串隐式转换为system.data.datatable

使用DataTable和序列化

此行错误

return serializer.Serialize(rows);

.cs代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;



namespace VOT.DashboardPages
{
    public partial class Velocity : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
                using (SqlConnection con = new SqlConnection(constr))
                {
                    using (SqlCommand cmd = new SqlCommand("SELECT ProjectNo FROM [dbo].[ProjectPlan] ORDER BY ProjectNo asc"))
                    {
                        cmd.CommandType = CommandType.Text;
                        cmd.Connection = con;
                        con.Open();
                        ddlProjectNo.DataSource = cmd.ExecuteReader();
                        ddlProjectNo.DataTextField = "ProjectNo";
                        ddlProjectNo.DataValueField = "ProjectNo";
                        ddlProjectNo.DataBind();
                        con.Close();
                    }
                }
                ddlProjectNo.Items.Insert(0, new ListItem("--Select ProjectNo--", "0"));
            }
        }

            public DataTable BindData(String prjNo)
            {
                DataTable dt = new DataTable();
                SqlConnection connection = new SqlConnection("constr");
                try
                {
                    connection.Open();
                    SqlCommand sqlcmd = new SqlCommand("VelocityByOperationType", connection);
                    sqlcmd.CommandType = CommandType.StoredProcedure;
                    SqlDataAdapter sqlDa = new SqlDataAdapter(sqlcmd);
                    sqlcmd.Parameters.AddWithValue("@prjNo", prjNo);
                    sqlDa.Fill(dt);
                    System.Web.Script.Serialization.JavaScriptSerializer serializer = new System.Web.Script.Serialization.JavaScriptSerializer();

                    List<Dictionary<string, object>> rows = new List<Dictionary<string, object>>();

                    Dictionary<string, object> row;
                    foreach (DataRow dr in dt.Rows)
                    {
                        row = new Dictionary<string, object>();
                        foreach (DataColumn col in dt.Columns)
                        {
                            row.Add(col.ColumnName, dr[col]);
                        }
                          rows.Add(row);
                    }

                    return serializer.Serialize(rows);

               }
                finally
                {
                    connection.Close();
                }
            }


    protected void ddlProjectNo_SelectedIndexChanged(object Sender,EventArgs e)
    {
        TextBox1.Text = ddlProjectNo.SelectedItem.Value;
        DataTable dt = BindData(ddlProjectNo.SelectedItem.Value);
        //if(dt.Rows.Count>0)
        //{

        //}
    }
}

}

Answer 1

Serialize方法返回一个字符串，而不是DataTable。

如果要从方法中返回数据表，则需要用以下内容替换返回的变量（第68行）：

return dt;

这将在调用该方法时从该方法返回具有DataRows的填充的DataTable。

例如，如果要返回DataRows的序列化字符串，则需要将方法签名从DataTable更改为string或创建一个新方法。

public string ReturnSerialisedData()
{
    // Add data table code here
    JavaScriptSerializer serializer = new JavaScriptSerializer();
    return serializer.Serialize(rows);
}

另外，您可能希望将代码分成更多服务/数据访问层，而不是直接在Page_Load事件中执行数据库操作。

我收到此错误，无法将字符串隐式转换为system.data.datatable

1 个答案: