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Read Entity objects from database using EntityDataReader

Due to some reason I need to read entity objects directly from database using ADO.Net.
I've found below snippet from Microsoft documentation. I want to know are there any methods to read whole row into an Onject ('contact' in this sample) using EntityDataReader instead of mapping every single field to every property? I mean instead of reading Contact.Id and Contact.Name and other fields one by one, are there any methods which read one row into one object or not?
using (EntityConnection conn =
new EntityConnection("name=AdventureWorksEntities"))
{
conn.Open();
string esqlQuery = #"SELECT VALUE contacts FROM
AdventureWorksEntities.Contacts AS contacts
WHERE contacts.ContactID == #id";
// Create an EntityCommand.
using (EntityCommand cmd = conn.CreateCommand())
{
cmd.CommandText = esqlQuery;
EntityParameter param = new EntityParameter();
param.ParameterName = "id";
param.Value = 3;
cmd.Parameters.Add(param);
// Execute the command.
using (EntityDataReader rdr =
cmd.ExecuteReader(CommandBehavior.SequentialAccess))
{
// The result returned by this query contains
// Address complex Types.
while (rdr.Read())
{
// Display CustomerID
Console.WriteLine("Contact ID: {0}",
rdr["ContactID"]);
// Display Address information.
DbDataRecord nestedRecord =
rdr["EmailPhoneComplexProperty"] as DbDataRecord;
Console.WriteLine("Email and Phone Info:");
for (int i = 0; i < nestedRecord.FieldCount; i++)
{
Console.WriteLine(" " + nestedRecord.GetName(i) +
": " + nestedRecord.GetValue(i));
}
}
}
}
conn.Close();
}

Your cleanest option is to use execute your query using EntityFramework as suggested by #herosuper
In your example, you'd need to do something like this:
EntityContext ctx = new EntityContext();
var contacts= ctx.Contacts
.SqlQuery("SELECT * FROM AdventureWorksEntities.Contacts AS contacts"
+ "WHERE contacts.ContactID =#id", new SqlParameter("#id", 3)).ToList();
From here, you would be able to:
var myvariable = contacts[0].ContactID;//zero is index of list. you can use foreach loop.
var mysecondvariable = contacts[0].EmailPhoneComplexProperty;
Alternatively, you might skip the whole SQL string by by doing this:
EntityContext ctx = new EntityContext();
var contact= ctx.Contacts.Where(a=> a.ContactID ==3).ToList();
I'm assuming the query returns more than one record, otherwise you would just use FirstOrDefault() instead of Where()

SQL Query not Retrieving All Rows in C# Application

I have a stored procedure created in my SQL Server 2012 database that selects data from multiple tables. In C#, I use this procedure to show data in a datagridview.
Issue: when I execute the query in SQL Server, I get the correct result which returns 3 rows, but in C#, it returns only 2 rows.
Query:
SELECT DISTINCT
Employee.Employee_No AS 'Badge'
,Employee.Employee_Name_Ar AS 'Emp Name'
,Employee.Basic_Salary AS 'Basic'
,Employee.Current_Salary AS 'Current'
,Attendance.Present
,Attendance.Leave
,Attendance.Othe_Leave AS 'OL'
,Pay_Slip.Salary_Amount AS 'Sal. Amt.'
,(ISNULL(Pay_Slip.OverTime1_Amount, 0.00) + ISNULL(Pay_Slip.OverTime2_Amount, 0.00)) AS 'O/T Amt.'
,(ISNULL(Pay_Slip.Salary_Amount, 0.00) + ISNULL(ISNULL(Pay_Slip.OverTime1_Amount, 0.00) + ISNULL(Pay_Slip.OverTime2_Amount, 0.00), 0.00)) AS 'Sal. & O/T'
,Pay_Slip.Trasnport AS 'Allow'
,Pay_Slip.CostofLiving AS 'O.Allow'
,Pay_Slip.Gross_Salary AS 'T Salary'
,Pay_Slip.Insurance1_Amount AS 'ss 7%'
,Pay_Slip.Insurance2_Amount AS 'ss 11%'
,(ISNULL(Pay_Slip.Insurance1_Amount, 0.00) + ISNULL(Pay_Slip.Insurance2_Amount, 0.00)) AS 'Total s.s'
,Pay_Slip.Tax
,Pay_Slip.Personal_Loans AS 'Advance'
,Pay_Slip.Other_Deductions AS 'Ded.'
,Pay_Slip.Net_Salary AS 'Net'
FROM Pay_Slip
LEFT JOIN Employee ON Pay_Slip.Employee_No = Employee.Employee_No
LEFT JOIN Attendance ON Pay_Slip.Employee_No = Attendance.Employee_No
WHERE Pay_Slip.Month = '5'
AND Pay_Slip.Year = '2020'
AND Attendance.Month = '5'
AND Attendance.Year = '2020'
Executing this query in SQL Server returns 3 rows which are the employee slips on May-2020 (They all have values in May-2020).
C# code:
private void dateTimePicker_ReportDate_ValueChanged(object sender, EventArgs e)
{
try
{
DateTime date = dateTimePicker_ReportDate.Value;
String Month = dateTimePicker_ReportDate.Value.ToString("MM");
String Year = dateTimePicker_ReportDate.Value.ToString("yyyy");
String str = "server=localhost;database=EasyManagementSystem;User Id=Jaz;Password=Jaz#2020;Integrated Security=True;";
String query = "Execute EMP_PAY_ATT_Selection #Month, #Year";
SqlConnection con = null;
con = new SqlConnection(str);
SqlCommand cmd= new SqlCommand(query, con);
cmd.Parameters.Add("#Month", SqlDbType.Int).Value = Convert.ToInt32(Month);
cmd.Parameters.Add("#Year", SqlDbType.Int).Value = Convert.ToInt32(Year);
SqlDataReader sdr;
con.Open();
sdr = cmd.ExecuteReader();
if (sdr.Read())
{
DataTable dt = new DataTable();
dt.Load(sdr);
dataGridView_Report.DataSource = dt;
dataGridView_Report.EnableHeadersVisualStyles = false;
dataGridView_Report.ColumnHeadersDefaultCellStyle.BackColor = Color.LightBlue;
}
else
{
dataGridView_Report.DataSource = null;
dataGridView_Report.Rows.Clear();
}
con.Close();
}
catch (Exception es)
{
MessageBox.Show(es.Message);
}
}
Again, when running this, it only returns 2 rows on the datagridview. While it should be 3 rows.
These are the tables:

The DbDataReader.Read method advances the reader to the next record.
There is no way to rewind a data reader. Any methods that you pass it to will have to use it from whatever record it is currently on.
If you want to pass the reader to DataTable.Load(), do not Read from it yourself. If you merely want to know if it contains records, use HasRows.

C# - Retrieving data from mysql then storing into variables

I have been trying a more efficient way to get and set data from my database in mysql to a variable. I've used a for loop to shorten the code and make it easier to read, though i can't think of a way to properly set other variables. Here's my code:
Note: I use 18 different local variables. (i.g ad, mnd, psk, pck, etc..)
for (int i = 1; i <= 18; i++) {
MySqlCommand cmd = dbConn.CreateCommand();
cmd.CommandText = "SELECT price from products where productID = '" + i + "'";
MySqlDataReader reader = cmd.ExecuteReader();
while (reader.Read()) {
ad = Convert.ToInt32(reader.ToString());
}
}
I am trying to retrieve the prices of 18 products from the database, but on this piece of code, I can only set one price. Any kind of help would be appreciated.

You assign all prices to 1 variable. Your code run like this
ad = 150; //sample price
ad = 240;
ad = 100;
...(18 times)
You have to use array instead of single variable.
Change your code to :
MySqlCommand cmd = dbConn.CreateCommand();
cmd.CommandText = "SELECT price from products where productID > 1 AND productID < 19" ;
MySqlDataReader reader = cmd.ExecuteReader();
int counter = 0;
while (reader.Read()) {
ad[counter++] = Convert.ToInt32(reader.ToString());
}

Okay, change your schema a bit, so you have
name | price | id
------------------------
'ad' 1.00 1
'mnd' 42.24 2
'psk' 6.66 3
'pck' 2.00 4
'etc' 9999.99 5
...
Then use Dapper like this,
using Dapper;
...
IDictionary<string, decimal> products;
using(var connection = new SqlConnection(GetConnectionString()))
{
connection.Open();
products = connection.Query("SELECT name, price FROM products;")
.ToDictionary(
row => (string)row.Name,
row => (decimal)row.Price);
}
then you can get whatever product you want like this,
var adPrice = products["ad"];
Once you have many products (a lot more than 18) you won't want to hold them all in memory at once but for now this would work well.

C# MySQL adding multiple of the same parameter with a loop

Update: as the original question was essentially answered, I've marked this as complete.
I have a C# project in which I'd like to query a database. The SQL query will SELECT from a table, and in the WHERE clause I want to filter the results from a pre-defined list of values specified in C#.
List<string> productNames = new List<string >() { "A", "B", "C" };
foreach (name in productNames)
{
string query = #"
SELECT *
FROM products
WHERE name IN (#name);";
// Execute query
MySqlCommand cmd = new MySqlCommand(query, dbConn);
cmd.Parameters.AddWithValue("name", name);
MySqlDataReader row = cmd.ExecuteReader();
while (row.Read())
{
// Process result
// ...
}
}
However I'm getting an error:
There is already an open DataReader associated with this Connection
which must be closed first
Is it not possible then to use a for loop to add parameters this way to a SELECT statement?

You need to dispose your object to not get the exception. However you don't need to iterate over values and run a query for every value in the list. Try the following code. It makes a parameter for every value and adds it to command to use in "IN (...)" clause.
Also "using" keywords handles disposing objects.
List<string> productsIds = new List<string>() { "23", "46", "76", "88" };
string query = #"
SELECT *
FROM products
WHERE id IN ({0});";
// Execute query
using (MySqlCommand cmd = new MySqlCommand(query, dbConn))
{
int index = 0;
string sqlWhere = string.Empty;
foreach (string id in productsIds)
{
string parameterName = "#productId" + index++;
sqlWhere += string.IsNullOrWhiteSpace(sqlWhere) ? parameterName : ", " + parameterName;
cmd.Parameters.AddWithValue(parameterName, id);
}
query = string.Format(query, sqlWhere);
cmd.CommandText = query;
using (MySqlDataReader row = cmd.ExecuteReader())
{
while (row.Read())
{
// Process result
// ...
}
}
}

You are doing few things wrong. Let me point out them:
Everything is fine in the first iteration of the loop, when you are in second iteration the First Reader associated with the command remains opened and that result in current error.
You are using Where IN(..) you you can specify the values within IN as comma separated so there is no need to iterate through parameters.
You can use String.Join method to construct this values with a comma separator.
Now take a look into the following code:
List<int> productsIds = new List<int>() { 23, 46, 76, 88 };
string idInParameter = String.Join(",", productsIds);
// Create id as comma separated string
string query = "SELECT * FROM products WHERE id IN (#productId);";
MySqlCommand cmd = new MySqlCommand(query, dbConn);
cmd.Parameters.AddWithValue("#productId", idInParameter);
MySqlDataReader row = cmd.ExecuteReader();
while (row.Read())
{
// Process result
// ...
}
Please note if the id field in the table is not integers then you have to modify the construction of idInParameter as like the following:
idInParameter = String.Join(",", productsIds.Select(x => "'" + x.ToString() + "'").ToArray());

Pass the comma separated productIds string instead of looping. Read more about IN here.
string productIdsCommaSeparated = string.Join(",", productsIds.Select(n => n.ToString()).ToArray())
string query = #"
SELECT *
FROM products
WHERE id IN (#productId);";
// Execute query
MySqlCommand cmd = new MySqlCommand(query, dbConn);
cmd.Parameters.AddWithValue("productId", productIdsCommaSeparated );
MySqlDataReader row = cmd.ExecuteReader();
while (row.Read())
{
// Process result
// ...
}
The error you are getting is because you do not close the MySqlDataReader. You must close it to get rid of error before you call ExecuteReader in next iteration but this is not proper way in this case.

From what I tried and tested seems best solution (especially for text column types) is to create a list of individual parameters and add it as a range the to the query and parameters.
e.g:
List<MySqlParameter> listParams = new List<MySqlParameter>();
for (int i = 0; i < listOfValues.Length; i++)
{
listParams.Add(new MySqlParameter(string.Format("#values{0}", i),
MySqlDbType.VarChar) { Value = listOfValues[i] });
}
string sqlCommand = string.Format("SELECT data FROM table WHERE column IN ({0})",
string.Join(",", listParams.Select(x => x.ParameterName)));
......
using (MySqlCommand command = new MySqlCommand(sqlCommand, connection)
{
............
command.Parameters.AddRange(listParams.ToArray());
............
}

Fastest way to update more than 50.000 rows in a mdb database c#

I searched on the net something but nothing really helped me. I want to update, with a list of article, a database, but the way that I've found is really slow.
This is my code:
List<Article> costs = GetIdCosts(); //here there are 70.000 articles
conn = new OleDbConnection(string.Format(MDB_CONNECTION_STRING, PATH, PSW));
conn.Open();
transaction = conn.BeginTransaction();
using (var cmd = conn.CreateCommand())
{
cmd.Transaction = transaction;
cmd.CommandText = "UPDATE TABLE_RO SET TABLE_RO.COST = ? WHERE TABLE_RO.ID = ?;";
for (int i = 0; i < costs.Count; i++)
{
double cost = costs[i].Cost;
int id = costs[i].Id;
cmd.Parameters.AddWithValue("data", cost);
cmd.Parameters.AddWithValue("id", id);
if (cmd.ExecuteNonQuery() != 1) throw new Exception();
}
}
transaction.Commit();
But this way take a lot of minutes something like 10 minutes or more. There are another way to speed up this updating ? Thanks.

Try modifying your code to this:
List<Article> costs = GetIdCosts(); //here there are 70.000 articles
// Setup and open the database connection
conn = new OleDbConnection(string.Format(MDB_CONNECTION_STRING, PATH, PSW));
conn.Open();
// Setup a command
OleDbCommand cmd = new OleDbCommand();
cmd.Connection = conn;
cmd.CommandText = "UPDATE TABLE_RO SET TABLE_RO.COST = ? WHERE TABLE_RO.ID = ?;";
// Setup the paramaters and prepare the command to be executed
cmd.Parameters.Add("?", OleDbType.Currency, 255);
cmd.Parameters.Add("?", OleDbType.Integer, 8); // Assuming you ID is never longer than 8 digits
cmd.Prepare();
OleDbTransaction transaction = conn.BeginTransaction();
cmd.Transaction = transaction;
// Start the loop
for (int i = 0; i < costs.Count; i++)
{
cmd.Parameters[0].Value = costs[i].Cost;
cmd.Parameters[1].Value = costs[i].Id;
try
{
cmd.ExecuteNonQuery();
}
catch (Exception ex)
{
// handle any exception here
}
}
transaction.Commit();
conn.Close();
The cmd.Prepare method will speed things up since it creates a compiled version of the command on the data source.

Small change option:
Using StringBuilder and string.Format construct one big command text.
var sb = new StringBuilder();
for(....){
sb.AppendLine(string.Format("UPDATE TABLE_RO SET TABLE_RO.COST = '{0}' WHERE TABLE_RO.ID = '{1}';",cost, id));
}
Even faster option:
As in first example construct a sql but this time make it look (in result) like:
-- declaring table variable
declare table #data (id int primary key, cost decimal(10,8))
-- insert union selected variables into the table
insert into #data
select 1121 as id, 10.23 as cost
union select 1122 as id, 58.43 as cost
union select ...
-- update TABLE_RO using update join syntax where inner join data
-- and copy value from column in #data to column in TABLE_RO
update dest
set dest.cost = source.cost
from TABLE_RO dest
inner join #data source on dest.id = source.id
This is the fastest you can get without using bulk inserts.

Performing mass-updates with Ado.net and OleDb is painfully slow. If possible, you could consider performing the update via DAO. Just add the reference to the DAO-Library (COM-Object) and use something like the following code (caution -> untested):
// Import Reference to "Microsoft DAO 3.6 Object Library" (COM)
string TargetDBPath = "insert Path to .mdb file here";
DAO.DBEngine dbEngine = new DAO.DBEngine();
DAO.Database daodb = dbEngine.OpenDatabase(TargetDBPath, false, false, "MS Access;pwd="+"insert your db password here (if you have any)");
DAO.Recordset rs = daodb.OpenRecordset("insert target Table name here", DAO.RecordsetTypeEnum.dbOpenDynaset);
if (rs.RecordCount > 0)
{
rs.MoveFirst();
while (!rs.EOF)
{
// Load id of row
int rowid = rs.Fields["Id"].Value;
// Iterate List to find entry with matching ID
for (int i = 0; i < costs.Count; i++)
{
double cost = costs[i].Cost;
int id = costs[i].Id;
if (rowid == id)
{
// Save changed values
rs.Edit();
rs.Fields["Id"].Value = cost;
rs.Update();
}
}
rs.MoveNext();
}
}
rs.Close();
Note the fact that we are doing a full table scan here. But, unless the total number of records in the table is many orders of magnitude bigger than the number of updated records, it should still outperform the Ado.net approach significantly...