We Keep Coding

Refering to view values one by one

I have the following code which establishing an SQL connection inside of a project I am working on. What I want to do is to create a for loop which contains a method and every time the loop repeats the method runs with a different value until all views of the returned query are used.
I can't figure out how to refer to every value of the view without saving the view to a list or an array first. Any ideas?
SqlConnection Con = new SqlConnection(#"Data Source=localhost\**;Initial Catalog=ML;User Id=sa;Password='**'");
string sql = #"select product_id,Name from E_PRODUCT_PROPERTY";
var mylist = new List<WineRating>();
using (var command = new SqlCommand(sql, Con))
{
Con.Open();
using (var reader = command.ExecuteReader())
{
while (reader.Read())
new WineRating { product_id = reader.GetInt32(0), Name = reader.GetString(1) };
///Here goes the code I suppose
method_name(reader.GetInt32(0), reader.GetString(1));
}
}
public static int method_name(int product_id, string Name)
{
int num = x *2;
Console.WriteLine(num + Name);
}

Perhaps like this:
using (var reader = command.ExecuteReader())
{
while (reader.Read())
{
MyMethodToPrintToScreen(reader.GetInt32(0), reader.GetString(1));
}
}
With the method to print to screen
private static void MyMethodToPrintToScreen(int id, string product)
{
//Do whatever you wish with the data: example
Console.WriteLine($"My id: {id} | Product: {product}");
}
Edit
Let me make it even more obvious(using your exact code):
SqlConnection Con = new SqlConnection(#"Data Source=localhost\**;Initial Catalog=ML;User Id=sa;Password='**'");
string sql = #"select product_id,Name from E_PRODUCT_PROPERTY";
var mylist = new List<WineRating>();
using (var command = new SqlCommand(sql, Con))
{
Con.Open();
using (var reader = command.ExecuteReader())
{
while (reader.Read())
{
method_name(reader.GetInt32(0), reader.GetString(1));
}
}
}

SQL query result assertion

I have put together the following method:
public static ArrayList DbQueryToArry()
{
string SqlCString = "connString";
SqlConnection connection = null;
ArrayList valuesList = new ArrayList();
connection = new SqlConnection(SqlCString);
connection.Open();
SqlCommand command = new SqlCommand("Select CLIENTNO, ACCOUNT_Purpose from audit.ACCOUNTS_AUDIT", connection);
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
valuesList.Add(Convert.ToString(reader[0]));
}
return valuesList;
}
I'd like to be able to run an assertion like this one:
var a = DbQueryToArry();
Assert.IsTrue(a.Contains("some value"));
Given reader [0]
valuesList.Add(Convert.ToString(reader[0]));
I only get the first column (CLIENTINFO) into the array and not the second (ACCOUNT_Purpose). How should I modify the code to get both ?
In addition, the returned values could be either a String or Int so would my current code version should be handling both ?
Thanks in advance.

If we switch from obsolete ArrayList to something like IEnumerable<T>:
public static IEnumerable<IDataRecord> DbQueryToArray(string sql) {
if (null == sql)
throw new ArgumentNullException(nameof(sql));
//TODO: do not hardcode connetcion string but read it (say, from Settings)
string SqlCString = "connString";
//DONE: Wrap IDisposable into using
using (SqlConnection connection = new SqlConnection(SqlCString)) {
connection.Open();
//DONE: Wrap IDisposable into using
using (SqlCommand command = new SqlCommand(sql, connection)) {
//DONE: Wrap IDisposable into using
using (SqlDataReader reader = command.ExecuteReader()) {
while (reader.Read()) {
yield return reader as IDataRecord;
}
}
}
}
}
then you can use Linq in order to query the result:
var a = DbQueryToArray("Select CLIENTNO, ACCOUNT_Purpose from audit.ACCOUNTS_AUDIT");
Assert.IsTrue(a.Any(record =>
Convert.ToString(record["CLIENTNO"]) == "some value"));
Assert.IsTrue(a.Any(record =>
Convert.ToString(record["ACCOUNT_Purpose"]) == "some other value"));
If you don't want execute query several times, you can materialize the results:
var a = DbQueryToArray("Select CLIENTNO, ACCOUNT_Purpose from audit.ACCOUNTS_AUDIT")
.ToList();
Assert.IsTrue(a.Any(record => Convert.ToString(record[0]) == "some value"));
Assert.IsTrue(a.Any(record => Convert.ToString(record[1]) == "some other value"));
Finally (see comments below), if we want to test if any field in any record has the value:
var a = DbQueryToArray("Select CLIENTNO, ACCOUNT_Purpose from audit.ACCOUNTS_AUDIT")
.SelectMany(line => {
// Flatten the cursor into IEnumerable<String>
string[] result = new string[line.FieldCount];
for (int i = 0; i < result.Length; ++i)
result[i] = Convert.ToString(line[i]);
return result;
});
a.Any(item => item == "some value");

It is because you only read the first value of the reader. Reader.Read() read each row one by one and Convert.ToString(reader[0])) means that you want to read the first column as string.

That's cause you are getting only the first column. You can do something like below by specifying the column name
while (reader.Read())
{
valuesList.Add(Convert.ToString(reader["CLIENTNO"]));
valuesList.Add(Convert.ToString(reader["ACCOUNT_Purpose"]));
}
Moreover, since you are converting all the columns to string; I would suggest to use a strongly typed collection like List<string> rather then ArrayList valuesList = new ArrayList();

The other answers are good, However some concerns
Lets stop using ArrayList, and use a List<T> instead
Lets use a using statement where you can
Note : I have used a ValueTuple to return more than 1 field
Example
public static List<(string clientNo, string account)> DbQueryToArray()
{
const string SqlCString = "connString";
var valuesList = new List<(string clientNo, string account)>();
using (var connection = new SqlConnection(SqlCString))
{
connection.Open();
using (var command = new SqlCommand("Select CLIENTNO, ACCOUNT_Purpose from audit.ACCOUNTS_AUDIT", connection))
{
var reader = command.ExecuteReader();
while (reader.Read())
valuesList.Add(((string)reader[0],(string)reader[1]) );
}
}
return valuesList;
}
Usage
var results = DbQueryToArray();
Assert.IsTrue(results.Any(x => x.clientNo == someValue || x.account == someValue));

best practice is to check first if the reader has rows
reader.HasRows
then close the reader and the connection
your code should look like this:
public static ArrayList DbQueryToArry()
{
string SqlCString = "connString";
SqlConnection connection = null;
ArrayList valuesList = new ArrayList();
connection = new SqlConnection(SqlCString);
using (connection)
{
connection.Open();
SqlCommand command = new SqlCommand("Select CLIENTNO, ACCOUNT_Purpose from audit.ACCOUNTS_AUDIT", connection);
SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
valuesList.Add(Convert.ToString(reader[0]));
valuesList.Add(Convert.ToString(reader[1])); // add to valuelist
}
}
reader.Close(); // close reader
} //dispose connection
return valuesList;
}

Use DataTable and SqlDataAdapter to get query result in form of table. Something like this:
string connString = #"your connection string here";
string query = "select * from table";
DataTable dataTable = new DataTable();
SqlConnection conn = new SqlConnection(connString);
SqlCommand cmd = new SqlCommand(query, conn);
conn.Open();
// create data adapter
SqlDataAdapter da = new SqlDataAdapter(cmd);
// this will query your database and return the result to your datatable
da.Fill(dataTable);
conn.Close();
da.Dispose();
Then you can use dataTable object to see if particular values exist.

C# ExecuteReader fails if condition

Why only the else condition runs? Postalcode column is float, City column is nvarchar. I think the fail is the string may be mistake.
private void txt_st_postalcode_Leave(object sender, EventArgs e)
{
using (var connection = new SqlConnection("Data Source=mypublicip\\SQLEXPRESS2017;Initial Catalog=studentreg; User = myusername; Password=mypassword;"))
{
connection.Open();
using (var command = new SqlCommand("SELECT City FROM Cities WHERE Postcode=#Postcode", connection))
{
command.Parameters.AddWithValue("#Postcode", "10101");
using (var reader = command.ExecuteReader())
{
string txt_st_postalcode = reader.Read() ?
reader[1] as string : ("City");
if (reader.Read())
{
txt_st_city.Text = reader.GetString(reader.GetOrdinal("City"));
}
else
{
MessageBox.Show("Sh*t!");
}
}
}
}
}

Not too sure how these postcodes work (different in the UK), but given that you're using ExecuteReader you appear to be expecting multiple results. As the comments have pointed out, you're currently reading the results twice; however, you should probably have some form of loop; for example:
using (var command = new SqlCommand("SELECT City FROM Cities WHERE Postcode=#Postcode", connection))
{
command.Parameters.AddWithValue("#Postcode", "10101");
using (var reader = command.ExecuteReader())
{
while (reader.Read())
{
string txt_st_postalcode = reader[0] as string;
//txt_st_city.Text = reader.GetString(reader.GetOrdinal("City"));
// Depends what you're doing here?
}
}
}
If you only expect a single result, try using ExecuteScalar() which will return a single result; for example:
using (var command = new SqlCommand("SELECT City FROM Cities WHERE Postcode=#Postcode", connection))
{
command.Parameters.AddWithValue("#Postcode", "10101");
txt_st_city.Text = command.ExecuteScalar();
}

Firstly, if you need to read PostCode from the reader, you have to select first. So, change your query.
using (var command = new SqlCommand("SELECT City, PostCode FROM Cities WHERE Postcode=#Postcode", connection))
Secondly, calling read once per row before getting data.
if (reader.Read())
{
txt_st_postalcode .Text = reader.GetString(reader.GetOrdinal("PostCode"));
txt_st_city.Text = reader.GetString(reader.GetOrdinal("City"));
}
else
{
MessageBox.Show("Sh*t!");
}

How to store multiple values in a struct array using SqlDataReader

I'd like to populate an User array with data from my SQL Server database using a SqlDataReader.
This is my code so far:
public struct User
{
public int id;
public string log;
public string password;
public User (int id1,string s, s2)
{
id=id1;
log =s;
password=s2;
}
}
User[] al = new User[50];
int i=0;
using (SqlConnection connection = new SqlConnection("string")
{
connection.Open();
SqlCommand command = new SqlCommand("Select [UserName], [Password]. from [TaUser]", connection);
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
// populate the al array with the datas from the 3 columns : ID, UserName, Password
}
}
connection.Close();
}
I know that if I had a simple arraylist I could just do al.Add(""), however, I struggle when it comes to struct arrays.

There are a lots of errors in your code.
First, your User constructor is invalid, it should be:
public User(int id1, string s, string s2)
Second, your query does not return user id.
Third, it would probably be better to use List instead of array.
With all that, this should work
List<User> userList = new List<User>() ;
using (SqlConnection connection = new SqlConnection("string")
{
connection.Open();
SqlCommand command = new SqlCommand("Select [Id], [UserName], [Password]. from [TaUser]", connection);
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
var id = reader.GetInt32(0);
var userName = reader.GetString(1);
var pwd = reader.GetString(2);
var user = new User(id, userName, pwd);
userList.Add(user);
}
}
connection.Close();
// if you really need an array, do it here
var al = userList.ToArray()

I'd advise doing something like this:
SqlDataReader dataReader = cmd.ExecuteReader();
DataTable dataTable = new DataTable();
dataTable.Load(dataReader);
Then read out of that DataTable like this:
string name = dataTable.Rows[0]["UserName"] as string;
Then fill your User struct with the gathered info. Job Done?

ADO.NET ExecuteReader Returns No Results

I'm updating some old legacy code and I ran into a problem with the
SqlCommand.ExecuteReader() method. The problem is that it's not returning any
results. However, using SqlDataAdapter.Fill(), I get results back from the
database. What am I doing wrong? How can I get results back using the data
reader?
var connectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ToString();
using (var sqlConnection = new SqlConnection(connectionString))
{
using (var sqlCommand = new SqlCommand())
{
sqlCommand.Connection = sqlConnection;
sqlCommand.CommandType = CommandType.Text;
sqlCommand.CommandText = "SELECT * FROM MyTable WHERE ID = 1";
sqlConnection.Open();
// This code works.
//var dataTable = new DataTable();
//using (var sqlDataAdapter = new SqlDataAdapter(sqlCommand))
//{
// sqlDataAdapter.Fill(dataTable);
//}
// This code is not working.
using (var sqlDataReader = sqlCommand.ExecuteReader())
{
while (sqlDataReader.Read())
{
// This fails because the data reader has no results.
var id = sqlDataReader.GetInt32(0);
}
}
}
}

Could it be that there is no Int32 in your results ?
var id = sqlDataReader.GetInt32(0); // <-- this might not be an Int32
Either try:
var id = sqlDataReader.GetValue(0);
Or cast to the correct type (BIGINT for example is Int64), not sure without seeing your data.

Try this..
var id = 0;
using (var sqlDataReader = sqlCommand.ExecuteReader())
{
while (sqlDataReader.Read())
{
id = sqlDataReader.GetInt32(sqlDataReader.GetOrdinal("ColName"));
}
}
I have moved the variable outside of the reader code or the variable will only be accessible inside that scope. I would avoid specifying the ordinal in the code, in case someone altered the columns in the DB.
Also, specify the columns in the SQL statement... SELECT ColName FROM ... and use params in the query

If you got to that line then it has results
Does not mean the value is not null
And you should not use a SELECT *
If may have a problem with an implicit cast
Try Int32
try
{
if(sqlDataReader.IsDBNull(0))
{
// deal with null
}
else
{
Int32 id = sqlDataReader.GetInt32(0);
}
}
catch (SQLexception Ex)
{
Debug.WriteLine(Ex.message);
}

var connectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ToString();
using (var sqlConnection = new SqlConnection(connectionString))
{
sqlConnection.Open();
string sql = "SELECT * FROM MyTable WHERE ID = 1";
using (var sqlCommand = new SqlCommand(sql, sqlConnection))
{
using (var sqlDataReader = sqlCommand.ExecuteReader())
{
while (sqlDataReader.Read())
{
// This fails because the data reader has no results.
var id = sqlDataReader.GetInt32(0);
}
}
}
}