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Read all record in sql table using SqlDataReader

I want to read all records from "product" table and create objects from each records.
it only gets one records from the database, any ideas might help ?
public IReadOnlyList<Product> Search(string name)
{
var result = new List<Product>();
using (var conn = new SqlConnection(connectionString))
{
if (name == null)
{
var command = new SqlCommand("SELECT * FROM Product ", conn);
conn.Open();
using var reader = command.ExecuteReader();
{
while (reader.Read())
{
var prod = new Product((int)reader["ID"], (string)reader["Name"],
(double)reader["Price"], (int)reader["Stock"], (int)reader["VATID"],
(string)reader["Description"]);
result.Add(prod);
reader.NextResult();
}
reader.Close();
conn.Close();
return result;
};
}
}

If you have several result sets, you should loop over them, i.e. you should put one more outer loop, e.g.
using var reader = command.ExecuteReader();
do {
while (reader.Read()) {
var prod = new Product(
Convert.ToInt32(reader["ID"]),
Convert.ToString(reader["Name"]),
Convert.ToDouble(reader["Price"]), // decimal will be better for money
Convert.ToInt32(reader["Stock"]),
Convert.ToInt32(reader["VATID"]),
Convert.ToString(reader["Description"])
);
result.Add(prod);
}
}
while (reader.NextResult());
Note outer do .. while loop since we always have at least one result set.

You use NextResult which advances the reader to the next result set. This makes sense if you have multiple sql queries and you'd use it after the while-loop. Here it's just unnecessary and wrong.
You are already advancing the reader to the next record with Read.
If I get rid of it, this error occur : Unable to cast object of type
'System.DBNull' to type 'System.String.
You can use IsDBNull:
int nameIndex = reader.GetOrdinal("Name");
string name = reader.IsDBNull(nameIndex) ? null : reader.GetString(nameIndex);
int descIndex = reader.GetOrdinal("Description");
string description = reader.IsDBNull(descIndex) ? null : reader.GetString(descIndex);
var prod = new Product((int)reader["ID"],
name,
(double)reader["Price"],
(int)reader["Stock"],
(int)reader["VATID"],
description);
Use it for every nullable column, for the numeric columns you could use nullable types like int?.

You have an error in your code:
Remove the line reader.NextResult();
NextResult is used for moving to next result set not next record.

Definitely remove the NextResult(). That does NOT move between individual records in the same query. Read() does this for you already. Rather, NextResult() allows you to include multiple queries in the same CommandText and run them all in one trip to the database.
Try this:
public IEnumerable<Product> Search(string name)
{
using (var conn = new SqlConnection(connectionString))
using (var command = new SqlCommand("SELECT * FROM Product ", conn))
{
if (!string.IsNullOrEmpty(name) )
{
command.CommandText += " WHERE Name LIKE #Name + '%'";
command.Parameters.Add("#Name", SqlDbType.NVarChar, 50).Value = name;
}
conn.Open();
using var reader = command.ExecuteReader();
{
while (reader.Read())
{
var prod = new Product((int)reader["ID"], reader["Name"].ToString(),
(double)reader["Price"], (int)reader["Stock"], (int)reader["VATID"],
reader["Description"].ToString());
yield return prod;
}
}
}
}

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.

How to get values in two indexes of a string list and assign them to two string variables C#

I'm implementing a method to return the result set that generated from the query and assign it to a string list. I have set to assign the id (id is a primary key) and name of selected db table line to index 0 and 1 in the string list. The code of that as follows,
public List<string>[] getTrafficLevel()
{
string query = "select * from traffictimeinfo where startTime<time(now()) and endTime>time(now());";
List<string>[] list = new List<string>[2];
list[0] = new List<string>();
list[1] = new List<string>();
if (this.openConnection() == true)
{
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader dataReader = cmd.ExecuteReader();
while (dataReader.Read())
{
list[0].Add(dataReader["timeslotid"] + "");
list[1].Add(dataReader["timeslotname"] + "");
}
dataReader.Close();
this.closeConnection();
return list;
}
else
{
return list;
}
}
What I want to know is how can i assign this values in two indexes into two string variables.
the method that i tried is as follows, is there anyone who knows how to implement this.. Thanks in advance..
public void predictLevel(List<String>resList)
{
string trafficTime, trafficLevel;
List<string>[]ansList = getTrafficLevel();
ansList[0] = # want to assign the string value into trafficTime string variable
ansList[1].ToString = # want to assign the string value into trafficLevel string variable
}

Have you considered using List of Tuples instead?
public List<Tuple<string,string>> getTrafficLevel()
{
string query = "select * from traffictimeinfo where startTime<time(now()) and endTime>time(now());";
List<Tuple<string,string>> list = new List<Tuple<string,string>>();
if (this.openConnection() == true)
{
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader dataReader = cmd.ExecuteReader();
while (dataReader.Read())
{
list.Add(new Tuple<string,string>(dataReader["timeslotid"] + "", dataReader["timeslotname"] + ""));
}
dataReader.Close();
this.closeConnection();
return list;
}
else
{
return list;
}
}
And your predictLevel method would be -
public void predictLevel(List<String>resList)
{
string trafficTime, trafficLevel;
List<Tuple<string,string>> ansList = getTrafficLevel();
trafficTime = ansList[0].Item1;
trafficLevel = ansList[0].Item2;
}

Can I create an anonymous type collection from a DataReader?

I have this code:
var query = "SELECT * FROM Cats";
var conn = new SqlConnection(sqlConnectionString);
conn.Open();
var cmd = new SqlCommand(query);
var reader = cmd.ExecuteReader();
while (reader.Read())
{
var CatName = reader.GetString(0);
var CatDOB = reader.GetDateTime(1);
var CatStatus = reader.GetInt32(2);
}
I'd like to pull the rows out into an anonymous type collection, which I'd normally do using LINQ to iterate, but I an not sure if it's possible due to the way you have to call .Read() each time to get the next row.
Is there a way to do this?

You can create helper generic method and let compiler infer type parameter:
private IEnumerable<T> Select<T>(DbDataReader reader, Func<DbDataReader, T> selector)
{
while(reader.Read())
{
yield return selector(reader);
}
}
usage:
var items = SelectFromReader(reader, r => new { CatName = r.GetString(0), CarDOB = r.GetDateTime(1), CatStatus = r.GetInt32(2) });
You can even make the method an extension method on DbDataReader:
public static IEnumerable<T> Select<T>(this DbDataReader reader, Func<DbDataReader, T> selector)
{
while (reader.Read())
{
yield return selector(reader);
}
}
and use it like that:
var items = reader.Select(r => new { CatName = r.GetString(0), CarDOB = r.GetDateTime(1), CatStatus = r.GetInt32(2) });

Here is an example of doing it with dynamic (which I think is easier to work with) but some may feel does not adhere to the letter of your question.
Call it like this:
var result = SelectIntoList("SELECT * FROM Cats",sqlconnectionString);
You could (like I did) put it into a static class in a separate file for easier maintanence.
public static IEnumerable<dynamic> SelectIntoList(string SQLselect, string connectionString, CommandType cType = CommandType.Text)
{
using (SqlConnection conn = new SqlConnection(connectionString))
{
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandType = cType;
cmd.CommandText = SQLselect;
conn.Open();
using (SqlDataReader reader = cmd.ExecuteReader())
{
if (reader.Read()) // read the first one to get the columns collection
{
var cols = reader.GetSchemaTable()
.Rows
.OfType<DataRow>()
.Select(r => r["ColumnName"]);
do
{
dynamic t = new System.Dynamic.ExpandoObject();
foreach (string col in cols)
{
((IDictionary<System.String, System.Object>)t)[col] = reader[col];
}
yield return t;
} while (reader.Read());
}
}
conn.Close();
}
}
}

It's possible, although not particularly neat. We'll need to create a new method that will allow us to create an empty sequence that allows for type inference off of a dummy value for starters:
public static IEnumerable<T> Empty<T>(T dummyValue)
{
return Enumerable.Empty<T>();
}
This lets us create a list of an anonymous type:
var list = Empty(new
{
CatName = "",
CatDOB = DateTime.Today,
CatStatus = 0
}).ToList();
(The item here isn't used.)
Now we can add our anonymous types to this list:
var cmd = new SqlCommand(query);
var reader = cmd.ExecuteReader();
while (reader.Read())
{
list.Add(new
{
CatName = reader.GetString(0),
CatDOB = reader.GetDateTime(1),
CatStatus = reader.GetInt32(2),
});
}
Of course, using a named type would likely be easier, so I would suggest using one unless there is a real compelling reason not to do so. That is especially true if you plan to use the list outside of the scope it's created in.

Technically, it may not answer your question, but simply don't use a reader. Instead use a SqlDataAdapter to Fill a DataSet, if you can. Take the 0th Table of that DataSet, and select a new anonymous object from the Rows collection.
using System.Data; // and project must reference System.Data.DataSetExtensions
var ds = new DataSet();
using (var conn = DbContext.Database.GetDbConnection())
using (var cmd = conn.CreateCommand())
{
cmd.CommandType = CommandType.Text;
cmd.CommandText = sqlText;
conn.Open();
(new SqlDataAdapter(cmd)).Fill(ds);
}
var rows = ds.Tables[0].AsEnumerable(); // AsEnumerable() is the extension
var anons = rows
.Select(r => new { Val = r["Val"] })
.ToList();

Read data from SqlDataReader

I have a SQL Server 2008 database and I am working on it in the backend. I am working on asp.net/C#
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
//how do I read strings here????
}
I know that the reader has values. My SQL command is to select just 1 column from a table. The column contains strings ONLY. I want to read the strings (rows) in the reader one by one. How do I do this?

using(SqlDataReader rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
var myString = rdr.GetString(0); //The 0 stands for "the 0'th column", so the first column of the result.
// Do somthing with this rows string, for example to put them in to a list
listDeclaredElsewhere.Add(myString);
}
}

string col1Value = rdr["ColumnOneName"].ToString();
or
string col1Value = rdr[0].ToString();
These are objects, so you need to either cast them or .ToString().

Put the name of the column begin returned from the database where "ColumnName" is. If it is a string, you can use .ToString(). If it is another type, you need to convert it using System.Convert.
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
string column = rdr["ColumnName"].ToString();
int columnValue = Convert.ToInt32(rdr["ColumnName"]);
}

while(rdr.Read())
{
string col=rdr["colName"].ToString();
}
it wil work

Thought to share my helper method for those who can use it:
public static class Sql
{
public static T Read<T>(DbDataReader DataReader, string FieldName)
{
int FieldIndex;
try { FieldIndex = DataReader.GetOrdinal(FieldName); }
catch { return default(T); }
if (DataReader.IsDBNull(FieldIndex))
{
return default(T);
}
else
{
object readData = DataReader.GetValue(FieldIndex);
if (readData is T)
{
return (T)readData;
}
else
{
try
{
return (T)Convert.ChangeType(readData, typeof(T));
}
catch (InvalidCastException)
{
return default(T);
}
}
}
}
}
Usage:
cmd.CommandText = #"SELECT DISTINCT [SoftwareCode00], [MachineID]
FROM [CM_S01].[dbo].[INSTALLED_SOFTWARE_DATA]";
using (SqlDataReader data = cmd.ExecuteReader())
{
while (data.Read())
{
usedBy.Add(
Sql.Read<String>(data, "SoftwareCode00"),
Sql.Read<Int32>(data, "MachineID"));
}
}
The helper method casts to any value you like, if it can't cast or the database value is NULL, the result will be null.

For a single result:
if (reader.Read())
{
Response.Write(reader[0].ToString());
Response.Write(reader[1].ToString());
}
For multiple results:
while (reader.Read())
{
Response.Write(reader[0].ToString());
Response.Write(reader[1].ToString());
}

I know this is kind of old but if you are reading the contents of a SqlDataReader into a class, then this will be very handy. the column names of reader and class should be same
public static List<T> Fill<T>(this SqlDataReader reader) where T : new()
{
List<T> res = new List<T>();
while (reader.Read())
{
T t = new T();
for (int inc = 0; inc < reader.FieldCount; inc++)
{
Type type = t.GetType();
string name = reader.GetName(inc);
PropertyInfo prop = type.GetProperty(name);
if (prop != null)
{
if (name == prop.Name)
{
var value = reader.GetValue(inc);
if (value != DBNull.Value)
{
prop.SetValue(t, Convert.ChangeType(value, prop.PropertyType), null);
}
//prop.SetValue(t, value, null);
}
}
}
res.Add(t);
}
reader.Close();
return res;
}

I would argue against using SqlDataReader here; ADO.NET has lots of edge cases and complications, and in my experience most manually written ADO.NET code is broken in at least one way (usually subtle and contextual).
Tools exist to avoid this. For example, in the case here you want to read a column of strings. Dapper makes that completely painless:
var region = ... // some filter
var vals = connection.Query<string>(
"select Name from Table where Region=#region", // query
new { region } // parameters
).AsList();
Dapper here is dealing with all the parameterization, execution, and row processing - and a lot of other grungy details of ADO.NET. The <string> can be replaced with <SomeType> to materialize entire rows into objects.

Actually, I figured it out myself that I could do this:
while (rdr.read())
{
string str = rdr.GetValue().ToString().Trim();
}

In the simplest terms, if your query returns column_name and it holds a string:
while (rdr.Read())
{
string yourString = rdr.getString("column_name")
}

I usually read data by data reader this way. just added a small example.
string connectionString = "Data Source=DESKTOP-2EV7CF4;Initial Catalog=TestDB;User ID=sa;Password=tintin11#";
string queryString = "Select * from EMP";
using (SqlConnection connection = new SqlConnection(connectionString))
using (SqlCommand command = new SqlCommand(queryString, connection))
{
connection.Open();
using (SqlDataReader reader = command.ExecuteReader())
{
if (reader.HasRows)
{
while (reader.Read())
{
Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1]));
}
}
reader.Close();
}
}

You have to read database columnhere. You could have a look on following code snippet
string connectionString = ConfigurationManager.ConnectionStrings["NameOfYourSqlConnectionString"].ConnectionString;
using (var _connection = new SqlConnection(connectionString))
{
_connection.Open();
using (SqlCommand command = new SqlCommand("SELECT SomeColumnName FROM TableName", _connection))
{
SqlDataReader sqlDataReader = command.ExecuteReader();
if (sqlDataReader.HasRows)
{
while (sqlDataReader.Read())
{
string YourFirstDataBaseTableColumn = sqlDataReader["SomeColumn"].ToString(); // Remember Type Casting is required here it has to be according to database column data type
string YourSecondDataBaseTableColumn = sqlDataReader["SomeColumn"].ToString();
string YourThridDataBaseTableColumn = sqlDataReader["SomeColumn"].ToString();
}
}
sqlDataReader.Close();
}
_connection.Close();

I have a helper function like:
public static string GetString(object o)
{
if (o == DBNull.Value)
return "";
return o.ToString();
}
then I use it to extract the string:
tbUserName.Text = GetString(reader["UserName"]);