SQL Server Express and C# : Database Charting
I am trying to link my SQL Server Express database to a chart in ac# application. I am trying to extract the age of some employees to display them in a bar char. Here is my code
string constring = "Data Source=.SQLEXPRESS;AttachDbFilename=C:UsersMichaelDownloadsEmployeeEmployeeEmployeeEmployeeDetails.mdf;Integrated Security=True;User Instance=True;Initial Catalog=Employee";
SqlConnection conDatabase = new SqlConnection(constring);
SqlCommand cmdDatabase = new SqlCommand("Select * from Employee;", conDatabase);
SqlDataReader myReader;
try{
conDatabase.Open();
myReader=cmdDatabase.ExecuteReader();
while(myReader.Read())
{
this.chart1.Series["Age"].Points.AddXY(myReader.GetString("FirstName"), myReader.GetInt32("Age"));
}
}
When I compile my program, I get 4 error messages, which relate to this line:
(myReader.GetString("FirstName"), myReader.GetInt32("Age"))
The error messages are:
The best overloaded method match for 'System.Data.Common.DbDataReader.GetString(int)' has some invalid arguments
Argument 1: cannot convert from 'string' to 'int' The best overloaded method match for 'System.Data.Common.DbDataReader.GetInt32(int)' has some invalid arguments
Argument 1: cannot convert from 'string' to 'int'
The SQL Server Express database uses VARCHAR for FirstName and INT for Age
what have i done wrong?
IDataReader 's .Get* methods only take the index of the column to be accessed, not the column name.
So instead of
myReader.GetString("FirstName")
You'll need something like
myReader["FirstName"].ToString()
and
Convert.ToInt32(myReader.GetInt32("Age")))
If you are doing this in a tight loop, then you can cache the name : index mappings.
Error 1 The best overloaded method match for 'System.Data.Common.DbDataReader.GetString(int)' has some invalid arguments
DbDataReader.GetString method takes argument as an int , not string .
Gets the value of the specified column as an instance of String.
public abstract string GetString(
int ordinal
)
Use this method with what is the zero-based column ordinal of your FirstName and Age columns.
Error 2 Argument 1: cannot convert from 'string' to 'int'
There is no implicit conversation from string to int . You get this error actually because myReader.GetString("FirstName") method returns string but your AddXY() method probably except int as a first parameter.
您应该使用GetString（0）或GetString（1）或GetString（2）
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