We Keep Coding

Pass logic function as parameter to general function

Trying to reduse some code and follow the DRY principle with a generic approach. The code is kind of trivial, but I can not manage to compile it. I guess you see what I'm trying to do here (not repeat GetData(), but rather have several Logic() func's), what am I doing wrong?
Caller:
IEnumerable<IMyClass> result = Factory.GetData<IEnumerable<IMyClass>>("storedProsedureName", Factory.LogicFunction());
Logic:
public static IEnumerable<T> GetData<T>(string storedProsedureName, Func<string, OracleConnection, OracleCommand, IEnumerable<T>> functionCall) where T : class
{
using (OracleConnection conn = new OracleConnection(Helpers.GetConnectionString()))
{
using (OracleCommand cmd = conn.CreateCommand())
{
try
{
return functionCall(storedProsedureName, conn, cmd);
}
catch (Exception e)
{
throw e;
}
}
}
}
public static IEnumerable<IMyClass> LogicFunction(string storedProsedureName= "", OracleConnection conn = null, OracleCommand cmd = null)
{
conn.Open();
{...}
conn.Close();
return IEnumerable<IMyClass>;
}
Error:
Argument 2: cannot convert
from
'System.Collections.Generic.IEnumerable_IMyClass>'
to
'System.Func_string, OracleConnection, OracleCommand, IEnumerable _IEnumerable_IMyClass>>>'

Change your caller to below code.
Removed () and also changed generic closing type from IEnumerable<IMyClass> to IMyClass.
IEnumerable<IMyClass> result = Factory.GetData<IMyClass>("storedProsedureName", Factory.LogicFunction);

MySql Connection Pool leaked after ThreadAbortedException

I updated the code in order to simplify it
I’ve encountered a strange issue that never happened before on this code (run perfectly for 2 years).
I’m running MVC application over multiple IISs, and using MySQL over C# code.
Querying table X receives response from a different table in the same schema.
The issue happens sporadically on some IIS (once a 1-4 days) and solved by 3 iisreset.
Here is the code I’m using (updated):
using (var conn = new MySqlConnection(connectionString))
{
var command = conn.CreateCommand();
command.CommandText = sql;
IDataReader reader;
try
{
reader = command.ExecuteReader();
}
catch (Exception ex)
{
throw new MoranbernateQueryException(sql, ex);
}
using (reader)
{
while (reader.Read())
{
Console.WriteLine(sql, GetTableFromReader(reader));
}
}
}
}
private static string GetTableFromReader(IDataReader reader)
{
var schema = reader.GetSchemaTable();
var rows = schema?.Rows;
if (rows != null && schema.Columns.Count > 11)
{
return rows[0][10].ToString();
}
}
The result of this code is an sql query to table A but the table (and data) from the reader schema is B. Both tables resides in the same DB and Schema.
Has anyone else encountered this type of problem? I’d like to hear any theory or suggestion for investigation.

i don't know how do you access reader even it out of scope, there is may problem with flow of your code. use below code i think this have to work.
using(var command = new MySqlConnection(connectionString))
{
command.CommandText = sql;
try
{
using(SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
var t = new T();
var i = 0;
foreach (var property in properties)
{
try
{
property.SetValue(t, reader.GetValue(i++));
}
catch (Exception ex)
{
HandleSetValueException<T>(sql, parameters, reader, connection, ex);
}
}
yield return t;
}
}
}
catch (Exception ex)
{
throw new MoranbernateQueryException(sql, ex);
}
}

So apparently it's a known issue that was fixed by MySql team, after updating the driver all is well for now

C# Mysql Connection must be valid and open

First of all: I got my code running without using oop. I declared all my variables inside the same class and opened/closed the connection right before and after passing the query to the db. That worked! Now with some new experiences I tried to split my code into different classes. Now it wont work anymore.
It tells me "Connection must be valid and open". Enough text, here's my current code:
Services.cs
public static MySqlConnection conn // Returns the connection itself
{
get
{
MySqlConnection conn = new MySqlConnection(Services.ServerConnection);
return conn;
}
}
public static string ServerConnection // Returns the connectin-string
{
get
{
return String.Format("Server={0};Port=XXXX;Database=xxx;Uid=xxx;password=xxXxxXxXxxXxxXX;", key);
}
}
public static void DB_Select(string s, params List<string>[] lists)
{
try
{
MySqlCommand cmd = conn.CreateCommand();
cmd.CommandType = CommandType.Text;
string command = s;
cmd.CommandText = command;
MySqlDataReader sqlreader = cmd.ExecuteReader();
while (sqlreader.Read())
{
if (sqlreader[0].ToString().Length > 0)
{
for (int i = 0; i < lists.Count(); i++)
{
lists[i].Add(sqlreader[i].ToString());
}
}
else
{
foreach (List<string> save in lists)
{
save.Add("/");
}
}
}
sqlreader.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error while selecting data from database!\nDetails: " + ex);
}
}
LoginForm.cs
private void checkUser(string username, string password)
{
using (Services.conn)
{
Services.conn.Open();
Services.DB_Select("..a short select statement..");
Services.conn.Close();
}
I guess this is all we need. I have shortened my code to get a focus on the problem.
I created Services.cs to get a global way to access the db from all forms without copy&pasting the connection info. Now when I reach my LoginForm.cs it throws an error "Connection must be valid and open". I've already debugged my code. It's all time closed. Even when passing conn.Open() it stays closed. Why?
Another try: I've also tried placing conn.Open() and conn.Close() inside Services.DB_Select(..) at the beginning and end. Same error here.
I have to say: The code worked before and I've used the same connection-string. So the string itself is surely valid.
I appreciate any help given here!

The problem is that you don't store the connection that was returned from your factory property. But don't use a property like a method. Instead use it in this way:
using (var con = Services.conn)
{
Services.conn.Open();
Services.DB_Select("..a short select statement..", con ));
//Services.conn.Close(); unnecessary with using
}
So use the same connection in the using that was returned from the property(or better created in the using) and pass it to the method which uses it. By the way, using a property as factory method is not best practise.
But in my opinion it's much better to create the connection where you use it, best place is in the using statement. And throw the con property to the garbage can, it is pointless and a source for nasty errors.
public static void DB_Select(string s, params List<string>[] lists)
{
try
{
using(var conn = new MySqlConnection(Services.ServerConnection))
{
conn.Open();
MySqlCommand cmd = conn.CreateCommand();
cmd.CommandText = s;
using( var sqlreader = cmd.ExecuteReader())
while (sqlreader.Read())
{
if (sqlreader[0].ToString().Length > 0)
{
for (int i = 0; i < lists.Count(); i++)
{
lists[i].Add(sqlreader[i].ToString());
}
}
else
{
foreach (List<string> save in lists)
{
save.Add("/");
}
}
} // unnecessary to close the connection
} // or the reader with the using-stetement
}
catch (Exception ex)
{
MessageBox.Show("Error while selecting data from database!\nDetails: " + ex);
}
}

Try to restructure your Services class as follows
public static MySqlConnection conn // Returns the connection itself
{
get
{
MySqlConnection conn = new MySqlConnection(Services.ServerConnection);
return conn;
}
}
private static string ServerConnection // Returns the connectin-string - PRIVATE [Improved security]
{
get
{
return String.Format("Server={0};Port=XXXX;Database=xxx;Uid=xxx;password=xxXxxXxXxxXxxXX;", key);
}
}
// Rather than executing result here, return the result to LoginForm - Future improvement
public static void DB_Select(MySqlConnection conn ,string s, params List<string>[] lists)
{
try
{
MySqlCommand cmd = conn.CreateCommand();
cmd.CommandType = CommandType.Text;
string command = s;
cmd.CommandText = command;
MySqlDataReader sqlreader = cmd.ExecuteReader();
while (sqlreader.Read())
{
if (sqlreader[0].ToString().Length > 0)
{
for (int i = 0; i < lists.Count(); i++)
{
lists[i].Add(sqlreader[i].ToString());
}
}
else
{
foreach (List<string> save in lists)
{
save.Add("/");
}
}
}
sqlreader.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error while selecting data from database!\nDetails: " + ex);
}
}
In LoginForm.cs use returning connection and store it there. When you need to execute query, use
MySqlConnection conn=Services.conn(); // Get a new connection
Services.DB_Select(conn,"..a short select statement.."); // Executing requirement
Services.conn.Close();
Additional - I suggest you need to return MySqlDataReader to LoginForm and handle results there

private MySqlConnection _conn;
public MySqlConnection conn // Returns the connection itself
{
get
{
if(_conn == null)
_conn = new MySqlConnection(Services.ServerConnection);
return _conn;
}
}

How to copy MySqlDataReader into an array and then loop throught the array?

I am new to C# so yes this should be a faily easy question but I can't seem to find the answer to it.
I have a method that query a database.
What I am trying to do here is handle the loop though the data outside the method.
public MySqlDataReader getDataSet(string query)
{
MySqlDataReader dataset = null;
MySqlConnection conn = new MySqlConnection(conn_string);
if (startConnection(conn) == true)
{
MySqlCommand cmd = new MySqlCommand(query, conn);
dataset = cmd.ExecuteReader();
closeConnection(conn);
}
return dataset;
}
what I could do is write a while loop just before the closeConnection(conn); line and handle the data. But, I don't want to do it inside this method and I want to do it somewhere else in my code.
In one of my forms I want to read the database on the load so here is what I tried to do
public newDepartment()
{
InitializeComponent();
inputDepartmentName.Text = "Hi";
dbConnetion db = new dbConnetion();
MySqlDataReader ds = db.getDataSet("SELECT name FROM test;");
while (ds.Read())
{
//Do Something
}
}
The problem that I am having is that I get an error Invalid attempt to Read when reader is closed
Which I belive I get this issue because I close the connection and then I am trying to read it. so What I need to do is read the data from the query and put it in an array and then loop through the array and deal with the data in a different form.
How can I workaround this issue? if my idea is good then how can I copy the data into an array and how do I loop though the array?
Here is the full class
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data.MySqlClient;
using System.Windows.Forms;
namespace POS
{
public class dbConnetion
{
//private OdbcConnection conn;
private readonly string mServer;
private readonly string mDatabase;
private readonly string mUid;
private readonly string mPassword;
private readonly string mPort;
private readonly string conn_string;
public dbConnetion()
{
mServer = "localhost";
mDatabase = "pos";
mUid = "root";
mPassword = "";
mPort = "3306";
conn_string = String.Format("server={0};user={1};database={2};port={3};password={4};", mServer, mUid, mDatabase, mPort, mPassword);
}
//Start connection to database
private bool startConnection(MySqlConnection mConnection)
{
try
{
mConnection.Open();
return true;
}
catch (MySqlException ex)
{
MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK);
return false;
}
}
//Close connection
private bool closeConnection(MySqlConnection mConnection)
{
try
{
mConnection.Close();
return true;
}
catch (MySqlException ex)
{
MessageBox.Show(ex.Message);
return false;
}
}
public MySqlDataReader getDataSet(string query)
{
MySqlDataReader dataset = null;
MySqlConnection conn = new MySqlConnection(conn_string);
if (startConnection(conn) == true)
{
MySqlCommand cmd = new MySqlCommand(query, conn);
dataset = cmd.ExecuteReader();
closeConnection(conn);
}
return dataset;
}
public void processQuery(string strSQL, List<MySqlParameter> pars)
{
MySqlConnection conn = new MySqlConnection(conn_string);
if (startConnection(conn) == true)
{
MySqlCommand cmd = new MySqlCommand(strSQL, conn);
foreach (MySqlParameter param in pars)
{
cmd.Parameters.Add(param);
}
cmd.ExecuteNonQuery();
closeConnection(conn);
}
}
}
}

Putting the records into an array would destroy the best feature of a using a datareader: that you only need to allocate memory for one record at a time. Try doing something like this:
public IEnumerable<T> getData<T>(string query, Func<IDataRecord, T> transform)
{
using (var conn = new MySqlConnection(conn_string))
using (var cmd = new MySqlCommand(query, conn))
{
conn.Open();
using (var rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
yield return transform(rdr);
}
}
}
}
While I'm here, there's a very serious security flaw with this code and the original. A method like this that only accepts a query string, with no separate mechanism for parameters, forces you to write code that will be horribly horribly vulnerable to sql injection attacks. The processQuery() method already accounts for this, so let's extend getDataset() to avoid that security issue as well:
public IEnumerable<T> getData<T>(string query, List<MySqlParameter> pars, Func<IDataRecord, T> transform)
{
using (var conn = new MySqlConnection(conn_string))
using (var cmd = new MySqlCommand(query, conn))
{
if (pars != null)
{
foreach(MySqlParameter p in pars) cmd.Parameters.Add(p);
}
conn.Open();
using (var rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
yield return transform(rdr);
}
}
}
}
Much better. Now we don't have to write code that's just asking to get hacked anymore. Here's how your newDepartment() method will look now:
public newDepartment()
{
InitializeComponent();
inputDepartmentName.Text = "Hi";
dbConnetion db = new dbConnetion();
foreach(string name in db.getDataSet("SELECT name FROM test;", null, r => r["name"].ToString() ))
{
//Do Something
}
}
One thing about this code is that is uses a delegate to have you provide a method to create a strongly-typed object. It does this because of the way the datareaders work: if you don't create a new object at each iteration, you're working on the same object, which can have undesirable results. In this case, I don't know what kind of object you're working with, so I just used a string based on what your SELECT query was doing.
Based on a separate discussion, here's an example of calling this for a more complicated result set:
foreach(var item in db.getDataSet(" long query here ", null, r =>
new columnClass()
{
firstname = r["firstname"].ToString(),
lastname = r["lastname"].ToString(),
//...
}
) )
{
//Do something
}

Since you are new to .Net I thought I point out that there are two layers of database access in ADO.Net. There are the data reader way that you are using and all of that is online only forward reading of queries. This is the lowest level access and will give you the best performance but it is more work. For most connection types you can only execute one command or have one active data reader per connection (And you can't close the connection before you have read the query as you are doing).
The other form is the offline data adapter and requires just a little bit different code, but is generally easier to use.
public DataTable getDataSet(string query)
{
MySqlConnection conn = new MySqlConnection(conn_string);
if (startConnection(conn) == true)
{
MySqlDataAdapter adapter = new MySqlDataAdapter(query, conn);
DataTable table = new DataTable();
adapter.Fill(table);
closeConnection(conn);
return table;
}
return null;
}
This will result in you getting a DataTable with columns and rows corresponding to the result of your query (Also look into command builders if you want to post changes back to the database later on from it, but for that you will need to keep the connection open).
One nice thing with using the data adapter is that it will figure out what the correct data types should be so you don't have to worry about invalid cast exceptions while reading the data from the data reader.
As somebody pointed out though you will need to read all the data into memory which could be a problem if you are dealing with a lot of memory. Also the DataTable class is really slow when you start dealing with a lot of records. Finally DataTable and DataSet classes also generally hook well into UI components in .Net so that their contents can easily be displayed to users.

.net SQL Server stored procs wrapper class structure

I'm looking to write a C# SQL Server wrapper to call some stored procedures. If I was writing a single function I'd do something like the following (which I think is correct/proper):
void RunStoredProc1(object arg1)
{
using(SqlConnection conn = new SqlConnection(connStr)){
try{
SqlCommand cmd = new SqlCommand("storedProc1", conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#input1", arg1);
conn.Open();
cmd.ExecuteNonQuery();
} catch (Exception ex){
//handle the exception appropriately.
}
}
}
The problem I'm having is that it seems like a lot of repeated code... every function will have the same using/try(open/execute)/catch code, and it'd be nice to have it all in only one place. Is there a clean way of doing this? How about for queries that I'd want to use a data reader on?

Something like this should do:
void RunStoredProc(string storedProcName, IDictionary<string, object> args)
{
using (SqlConnection conn = new SqlConnection(connStr))
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = storedProcName;
cmd.CommandType = CommandType.StoredProcedure;
foreach (KeyValuePair<string, object> kvp in args)
{
cmd.Parameters.AddWithValue(kvp.Key, kvp.Value);
}
conn.Open();
cmd.ExecuteNonQuery();
}
}
The connection object itself would probably also be better off as a parameter to this helper method, so you could make it static. It might be interesting to write it as an extension method on SqlConnection.
I would keep the exception handling in your RunStoredProc1 method or even more likely: in the methods that call RunStoredProc1, because exception handling will likely differ on a case by case basis.
void RunStoredProc1(object input1)
{
var args = new Dictionary<string, object>()
{
{ "input1", input1 }
};
try
{
RunStoredProc("storedProc1", args);
}
catch (Exception ex)
{
// Handle exception properly
}
}

Just a fun exercise for me, and not necessarily the way you'd want to implement it. I wrote a quick fluent interface for building and executing SqlCommands.
A couple of sample usages:
int i = Sql.UsingConnection("sample")
.GetTextCommandFor("Select Top 1 ActorID From Actor Where FirstName = #fname")
.AddParameters(new {fname = "Bob"})
.OnException(e => Console.WriteLine(e.Message))
.ExecuteScalar<int>();
var q = Sql.UsingConnection("sample")
.GetTextCommandFor("Select * From Actor Where FirstName=#fname and ActorID > #id")
.AddParameters(new {id = 1000, fname = "Bob"});
using(var reader = q.ExecuteReader())
{
while(reader.Read())
{
// do something
}
}
The actual class(es) and Interfaces are below:
public class Sql
{
public static ISqlCommandTypeSelector UsingConnection(string connection)
{
return new SqlBuilder(connection);
}
private class SqlBuilder : ISqlCommandTypeSelector, ISqlParameterManager, ISqlExecutor
{
private string _connection;
private string _sqltext;
private CommandType _commandtype;
private Action<Exception> _exceptionBehavior = DefaultExceptionBehavior;
private IList<SqlParameter> _inParams;
public SqlBuilder(string connection)
{
_connection = ConfigurationManager.ConnectionStrings[connection].ConnectionString;
_inParams = new List<SqlParameter>();
}
public ISqlParameterManager GetTextCommandFor(string text)
{
_sqltext = text;
_commandtype = CommandType.Text;
return this;
}
public ISqlParameterManager GetProcCommandFor(string proc)
{
_sqltext = proc;
_commandtype = CommandType.StoredProcedure;
return this;
}
public ISqlExecutor OnException(Action<Exception> action)
{
_exceptionBehavior = action;
return this;
}
public void ExecuteNonQuery()
{
try
{
using (var connection = new SqlConnection(_connection))
using (var cmd = connection.CreateCommand())
{
ConfigureCommand(cmd);
PopulateParameters(cmd);
connection.Open();
cmd.ExecuteNonQuery();
}
}
catch(Exception ex)
{
_exceptionBehavior(ex);
}
}
public T ExecuteScalar<T>()
{
T result = default(T);
try
{
using (var connection = new SqlConnection(_connection))
using (var cmd = connection.CreateCommand())
{
ConfigureCommand(cmd);
PopulateParameters(cmd);
connection.Open();
result = (T) cmd.ExecuteScalar();
return result;
}
}
catch(InvalidCastException ex)
{
// rethrow?
}
catch(Exception ex)
{
_exceptionBehavior(ex);
}
return result;
}
public IDataReader ExecuteReader()
{
try
{
var connection = new SqlConnection(_connection);
var cmd = connection.CreateCommand();
ConfigureCommand(cmd);
PopulateParameters(cmd);
connection.Open();
var reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
return reader;
}
catch(Exception ex)
{
_exceptionBehavior(ex);
}
return null;
}
public ISqlExecutor AddParameters(object #params)
{
var type = #params.GetType();
var props = type.GetProperties();
foreach (var propertyInfo in props)
{
var param = new SqlParameter("#" + propertyInfo.Name, propertyInfo.GetValue(#params, null));
param.Direction = ParameterDirection.Input;
_inParams.Add(param);
}
return this;
}
public ISqlExecutor WithoutParams()
{
return this;
}
private void ConfigureCommand(SqlCommand cmd)
{
cmd.CommandText = _sqltext;
cmd.CommandType = _commandtype;
}
private void PopulateParameters(SqlCommand cmd)
{
cmd.Parameters.AddRange(_inParams.ToArray());
}
private static void DefaultExceptionBehavior(Exception e)
{
// do something
}
}
}
public interface ISqlCommandTypeSelector
{
ISqlParameterManager GetTextCommandFor(string text);
ISqlParameterManager GetProcCommandFor(string proc);
}
public interface ISqlExecutor
{
ISqlExecutor OnException(Action<Exception> action);
void ExecuteNonQuery();
T ExecuteScalar<T>();
IDataReader ExecuteReader();
}
public interface ISqlParameterManager
{
ISqlExecutor AddParameters(object #params);
ISqlExecutor WithoutParams();
}
There is some repeated code that could probably be refactored some more if you really hate repeated code. This is just a fun exercise, and probably not how you want to do your data access however. This also doesn't support out parameters as it is written.

The Microsoft Enterprise Library Data Access Application Block can help to reduce redundant code like that, if you're sticking to pure ADO.NET for your data layer. See http://msdn.microsoft.com/en-us/library/ff664408(v=PandP.50).aspx. There are lots of code samples online and in the download as well, i.e. http://msdn.microsoft.com/en-us/library/ff664702(v=PandP.50).aspx.

I'm a big fan of letting computers do the rote, repetitive work. They're very good at it. I only have to teach them to do it once. So I wrote a code generator that uses a reference database to generate strongly typed access code. The advantage of this technique is that if you change the stored procedure's signatures, all you have to do it re-gen your data access layer. Any breaking changes will cause compile errors.
The code generate I wrote reads an XML file identifying the stored procedures of interest and retrieves their metadata from the specified reference database(s).
The XML file contains flags identifying whether each stored procedure returns
multiple result sets (dataset)
a single result set (datatable)
a single row (datarow)
a single row with a single column (a scalar value)
a DataReader
an XmlReader
or nothing (nonquery)
From that it generates appropriate code, 1 class per stored procedure. The generated code provides access to the stored procedure's return code as well as the returned value for any output parameters.
It also parses the declaration for the stored procedure in the stored procedure's source code to identify any optional arguments (those with default values): the generated code allows those to be omitted in the call to execute the stored procedure.
Invoking the generated code goes like this:
public DataTable GetRiskFactorsForPatient( int patientID )
{
dbo_GetRiskbyPatient sp = new dbo_GetRiskbyPatient( CONNECT_STRING_ID ) ;
int rc = sp.Exec( patientID ) ;
DataTable dt = sp.ResultSet ;
if ( dt == null ) throw new InvalidOperationException( "nothing returned from stored procedure" ) ;
return dt ;
}

Personally, i prefer
void RunStoredProc1(object arg1)
{
try
{
using(SqlConnection conn = new SqlConnection(connStr))
{
using SqlCommand cmd = new SqlCommand("storedProc1", conn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#input1", arg1);
conn.Open();
cmd.ExecuteNonQuery();
}
}
}
catch (Exception ex)
{
//handle the exception appropriately.
}
}
Over the traditional try catch finally that you would need to do to manage your resources.
But overall, I like doing it with separate methods, so that you can custom tailor your catch blocks for the sproc.
Also, You might need more than one parameter down the road, and you would just be making a mess of a fairly straight-forward function