从SQL数据库创建图表 [英] Create chart from SQL database

问题描述

我对这部分代码有问题，给我看错：在整数类型上转换字符串ID无效。在SQL中是int类型。请问哪里有问题？谢谢

 Chart1.Series（GRAF_PORUCH）。Points.AddXY（READER.GetInt32（ID），READER.GetString（ VIDENCNI_CIS））

我的尝试：

私有子BUTTON1_Click（发件人为对象，e为EventArgs）处理BUTTON1.Click 
 
 Dim DOTAZ As String =SELECT * FROM TECH_PORUCHY
 Dim READER As SqlDataReader 
 Dim ds As New DataSet 
 Try 
 CONNECTION.Open（）
 
 CMD6 =新SqlCommand（DOTAZ，CONNECTION）
 READER = CMD6.ExecuteReader 
当READER.Read 
 
 Chart1.Series（GRAF_PORUCH）。XValueMember =EVIDENCNI_CIS
 Chart1.Series（GRAF_PORUCH）。YValueMembers = ID
 Chart1.Size = New System.Drawing.Size（780,350）
 Chart1.Series（GRAF_PORUCH）。Points.AddXY（READER.GetInt32（ID），READER.GetString （VIDENCNI_CIS））
 En d $ 
 CONNECTION.Close（）
 
 Catch ex As Exception 
 MessageBox.Show（ex.Message）
最后
 CONNECTION.Dispose（）
 
结束尝试
结束子
 

解决方案

如果查看文档 - < a href =https://docs.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqldatareader.getint32?view=netframework-4.7.2> SqlDataReader.GetInt32（Int32）方法（系统.Data.SqlClient）| Microsoft Docs [ ^ ] - 它会显示

Quote：

public override int GetInt32（ int i）;

参数

i Int32 从零开始的列序数。

您正在使用字符串在你的代码

 ... AddXY（READER.GetInt32（ID），... 

注意你会遇到与<$相同的问题c $ c> GetString 。



您还将使用

SELECT *返回表格中的所有列FROM TECH_PORUCHY

最好明确列出要返回的列 - 它还可以使用 GetInt32 等代码更容易阅读.Eg < pre lang =vb> Dim DOTAZ As String = SELECT ID，VIDENCNI_CIS FROM TECH_PORUCHY
。
。
。
Chart1.Series（ GRAF_PORUCH）。Points.AddXY（READER.GetInt32（< span class =code-digit> 0 ），READER.GetString（ 1 ））

I have a problem with this part of code, show me error: convert string ID on type integer is not valid. In SQL is type int. Where is a problem please? Thank you

Chart1.Series("GRAF_PORUCH").Points.AddXY(READER.GetInt32("ID"), READER.GetString("VIDENCNI_CIS"))

What I have tried:

Private Sub BUTTON1_Click(sender As Object, e As EventArgs) Handles BUTTON1.Click

       Dim DOTAZ As String = "SELECT * FROM TECH_PORUCHY"
       Dim READER As SqlDataReader
       Dim ds As New DataSet
       Try
           CONNECTION.Open()

           CMD6 = New SqlCommand(DOTAZ, CONNECTION)
           READER = CMD6.ExecuteReader
           While READER.Read

               Chart1.Series("GRAF_PORUCH").XValueMember = "EVIDENCNI_CIS"
               Chart1.Series("GRAF_PORUCH").YValueMembers = "ID"
               Chart1.Size = New System.Drawing.Size(780, 350)
               Chart1.Series("GRAF_PORUCH").Points.AddXY(READER.GetInt32("ID"), READER.GetString("VIDENCNI_CIS"))
           End While
           CONNECTION.Close()

       Catch ex As Exception
           MessageBox.Show(ex.Message)
       Finally
           CONNECTION.Dispose()

       End Try
   End Sub

解决方案

If you check the documentation - SqlDataReader.GetInt32(Int32) Method (System.Data.SqlClient) | Microsoft Docs[^] - it will show you

Quote:

public override int GetInt32 (int i);
Parameters
i Int32 The zero-based column ordinal.

You are using a string in your code

... AddXY(READER.GetInt32("ID"), ...

Note you will have the same problem with GetString.

You are also returning all of the columns from your table with

"SELECT * FROM TECH_PORUCHY"

It is better practice to explicitly list the columns you want to return - it also makes code using GetInt32 etc easier to read.E.g.

Dim DOTAZ As String = "SELECT ID, VIDENCNI_CIS FROM TECH_PORUCHY"
.
.
.
Chart1.Series("GRAF_PORUCH").Points.AddXY(READER.GetInt32(0), READER.GetString(1))

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