I'm developing a C# solution with data access to Oracle.
And would like to have a generic solution about query.
Here is a part of my code :
public DataTable GetData(string query)
{
DbProviderFactory factory = DbProviderFactories.GetFactory("System.Data.OracleClient");
using (DbConnection conn = factory.CreateConnection())
{
try
{
DbConnectionStringBuilder csb = factory.CreateConnectionStringBuilder();
csb["Data Source"] = #"Northwind";
csb["User Id"] = #"Northwind";
csb["Password"] = #"Northwind";
conn.ConnectionString = csb.ConnectionString;
conn.Open();
using (DbCommand cmd = conn.CreateCommand())
{
cmd.CommandText = query;
using (DataTable dt = new DataTable())
{
DbDataAdapter da = factory.CreateDataAdapter();
cmd.CommandType = CommandType.Text;
da.SelectCommand = cmd;
da.Fill(dt);
return dt;
}
}
}
catch (Exception ex)
{
throw new Exception("Error", ex);
}
finally
{
if (conn.State != ConnectionState.Closed)
conn.Close();
}
}
}
And I call my method like this :
DataAccess.Provider data = new DataAccess.Provider();
DataTabel dt = dt.GetData("select * from myTable);
This works pretty good but this is not my aim.
I have a second class called CL_mpg with all my SQL queries.
class CL_MPG
{
public string rq_sql;
public string selectParam(string param)
{
this.rq_sql = "select * from myTable where id = '" + param + "';";
return this.rq_sql;
}
public string select()
{
this.rq_sql = "select * from myTable";
return this.rq_sql;
}
//...
}
And I would like to use my methods selectParam and/or select to fill my datatable, but I don't know how to do that.
Although others complain at your learning attempt, everyone has to start somewhere. Your method is actually an ok start, but I would change the parameter from a string to a DbCommand object. Then, you can create your methods to properly build the command and set proper parameters. Then pass the entire prepared command to your wrapper method (that creates connection, tests open successful, queries data, etc) and have your method return a DataTable object as you have... something like
public class CL_MPG
{
private DataTable GetData(DbCommand cmd )
{
// do all the same as you have with exception of your USING DBCOMMAND.
// just set the connection property of the incoming command to that of
// your connection created
// AT THIS PART --
// using (DbCommand cmd = conn.CreateCommand())
// {
// cmd.CommandText = query;
// just change to below and remove the closing curly bracket for using dbcommand
cmd.Connection = conn;
}
// Now, your generic methods that you want to expose for querying
// something like
public DataTable GetAllData()
{
DbCommand cmd = new DbCommand( "select * from YourTable" );
return GetData( cmd );
}
public DataTable GetUser( int someIDParameter )
{
DbCommand cmd = new DbCommand( "select * from YourTable where ID = #parmID" );
cmd.Parameters.Add( "#parmID", someIDParameter );
return GetData( cmd );
}
public DataTable FindByLastName( string someIDParameter )
{
DbCommand cmd = new DbCommand( "select * from YourTable where LastName like #parmTest" );
cmd.Parameters.Add( "#parmTest", someIDParameter );
return GetData( cmd );
}
}
Notice the command is being built and fully prepared and parameterized vs concatination of strings as prior comment was made which could expose you to SQL-injection. As for the parameters, and not querying Oracle, they may need to be tweaked some. Different engines use slightly different conventions. If connecting to SQL-Server database, it uses "#" to identify a parameter. In SyBase Advantage Database, it uses ":". Using Visual FoxPro, a simple "?" placeholder is used.
Also, if your query has many criteria, just keep adding additional "#parm" type placeholders, then add your parameters in the same order as they appear in your query just to make sure you didn't miss any. Some functions could have none, one or more based on your needs. Then, in the samples provided, its as simple as doing something like
DataTable whoIs = yourCL_MPGObject.GetUser( 23 );
if( whoIs.Rows.Count > 0 )
MessageBox.Show( whoIs.Rows[0]["WhateverColumnName"] );
Related
I am using EF6 to query a backend database. User can customize a temporary table and query the data from the temporary table. I am using
DataTable result = context.Query(queryStatement);
to get the result and it has been working fine.
Now the query is needed among a serious of other sqlcommand and a transaction is needed. So I have
public static DataTable GetData()
{
using (MyDbContext context = new MyDbContext())
using (DbContextTransaction tran = context.Database.BeginTransaction())
{
try
{
int rowAffected = context.Database.ExecuteSqlCommand(
"UPDATE [MyDb].dbo.[TableLocks] SET RefCount = RefCount + 1 WHERE TableName = 'TESTTABLE1'");
if (rowAffected != 1)
throw new Exception("Cannot find 'TestTable1'");
//The following line will raise an exception
DataTable result = context.Query("SELECT TOP 100 * FROM [MyDb].dbo.[TestTable1]");
//This line will work if I change it to
//context.Database.ExecuteSqlCommand("SELECT TOP 100 * FROM [MyDb].dbo.[TestTable1]");
//but I don't know how to get the result out of it.
context.Database.ExecuteSqlCommand(
"UPDATE [MyDb].dbo.[TableLocks] SET RefCount = RefCount - 1 WHERE TableName = 'TestTable1'");
tran.Commit();
return result;
}
catch (Exception ex)
{
tran.Rollback();
throw (ex);
}
}
}
But this throws an exception while executing context.Query
ExecuteReader requires the command to have a transaction when the connection
assigned to the command is in a pending local transaction. The Transaction
property of the command has not been initialized.
And when I read this article: https://learn.microsoft.com/en-us/ef/ef6/saving/transactions
It says:
Entity Framework does not wrap queries in a transaction.
Is it the reason cause this issue?
How can I use context.Query() inside a transaction?
What else I can use?
I tried all other method, none of them work - because the return datatype cannot be predicted before hand.
I just realized that, the Query method is defined in MyDbContext!
public DataTable Query(string sqlQuery)
{
DbProviderFactory dbFactory = DbProviderFactories.GetFactory(Database.Connection);
using (var cmd = dbFactory.CreateCommand())
{
cmd.Connection = Database.Connection;
cmd.CommandType = CommandType.Text;
cmd.CommandText = sqlQuery;
using (DbDataAdapter adapter = dbFactory.CreateDataAdapter())
{
adapter.SelectCommand = cmd;
DataTable dt = new DataTable();
adapter.Fill(dt);
return dt;
}
}
}
May be you are missing this section -
you are free to execute database operations either directly on the
SqlConnection itself, or on the DbContext. All such operations are
executed within one transaction. You take responsibility for
committing or rolling back the transaction and for calling Dispose()
on it, as well as for closing and disposing the database connection
And then this codebase -
using (var conn = new SqlConnection("..."))
{
conn.Open();
using (var sqlTxn =
conn.BeginTransaction(System.Data.IsolationLevel.Snapshot))
{
try
{
var sqlCommand = new SqlCommand();
sqlCommand.Connection = conn;
sqlCommand.Transaction = sqlTxn;
sqlCommand.CommandText =
#"UPDATE Blogs SET Rating = 5" +
" WHERE Name LIKE '%Entity Framework%'";
sqlCommand.ExecuteNonQuery();
using (var context =
new BloggingContext(conn, contextOwnsConnection: false))
{
context.Database.UseTransaction(sqlTxn);
var query = context.Posts.Where(p => p.Blog.Rating >= 5);
foreach (var post in query)
{
post.Title += "[Cool Blog]";
}
context.SaveChanges();
}
sqlTxn.Commit();
}
catch (Exception)
{
sqlTxn.Rollback();
}
}
}
Specially this one -
context.Database.UseTransaction(sqlTxn);
Sorry guys, as mentioned above, I thought the Query method is from EF, but I examined the code and found it is actually coded by another developer, defined in class MyDbContext. Since this class is generated by EF, and I never think somebody have added a method.
It is
public DataTable Query(string sqlQuery)
{
DbProviderFactory dbFactory = DbProviderFactories.GetFactory(Database.Connection);
using (var cmd = dbFactory.CreateCommand())
{
cmd.Connection = Database.Connection;
cmd.CommandType = CommandType.Text;
cmd.CommandText = sqlQuery;
//And I added this line, then problem solved.
if (Database.CurrentTransaction != null)
cmd.Transaction = Database.CurrentTransaction.UnderlyingTransaction;
using (DbDataAdapter adapter = dbFactory.CreateDataAdapter())
{
adapter.SelectCommand = cmd;
DataTable dt = new DataTable();
adapter.Fill(dt);
return dt;
}
}
}
Im trying to build up a little status-tool. I need to get results of multiple queries (about 4-5). The general connection-setup and 'how-to-read-data' is already done but I cant figure out how the another query executed.
Everything I found while searching for it is for the SqlClient. Im totally overcharged with this.
Here is my code so far (be patient, im a newbie to this):
private void button1_Click(object sender, EventArgs e)
{
if(listView1.Items.Count > 1)
{
listView1.Items.Clear();
}
var listMember = new List<string>{};
var listOnline = new List<string>{};
// SQL PART //
string connString = "Server=10*****;Port=3306;Database=e***;Uid=e***;password=********************;";
MySqlConnection conn = new MySqlConnection(connString);
MySqlCommand command = conn.CreateCommand();
command.CommandText = "SELECT fullname,online FROM member WHERE active = '1' ORDER BY online DESC";
try
{
conn.Open();
}
catch (Exception ex)
{
listView1.Items.Add("Error: " + ex);
}
MySqlDataReader reader = command.ExecuteReader();
while(reader.Read())
{
listMember.Add(reader["fullname"].ToString());
listOnline.Add(reader["online"].ToString());
}
conn.Close();
// SQL ENDING //
// SET ENTRIES TO LISTVIEW //
int counter = 0;
foreach(string member in listMember)
{
ListViewItem item = new ListViewItem(new[] { member, listOnline.ElementAt(counter) });
item.ForeColor = Color.Green;
listView1.Items.Add(item);
counter++;
}
}
Im not really sure how the design/layout will look like in the end, so I would like to just append the results to lists in the sql-part to process the data later out of the lists.
Do I really have to setup a complete new connection after conn.Close()? Or is there any other way? I can just imagine: 5 queries with their own connection,try,catch and 2 loops... this will get about 100-200 lines just for getting the results out of 5 queries. Isnt that a bit too much for such an easy thing?
Hope for some help.
Greetings.
According to the new comments my latest code:
Top:
public partial class Form1 : Form
{
public static string connString = "Server=10****;Port=3306;Database=e****;Uid=e****;password=****;";
public Form1()
{
InitializeComponent();
MySqlConnection conn = new MySqlConnection(connString); // Error gone!
}
Body part:
public void QueryTwoFields(string s, List<string> S1, List<string> S2)
{
try
{
MySqlCommand cmd = conn.CreateCommand(); // ERROR: conn does not exist in the current context.
cmd.CommandType = CommandType.Text;
string command = s;
cmd.CommandText = command;
MySqlDataReader sqlreader = cmd.ExecuteReader();
while (sqlreader.Read())
{
S1.Add(sqlreader[0].ToString());
S2.Add(sqlreader[1].ToString());
}
sqlreader.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private void button1_Click(object sender, EventArgs e)
{
if(listView1.Items.Count > 1)
{
listView1.Items.Clear();
}
var listMember = new List<string>{};
var listOnline = new List<string>{};
using (conn) // ERROR: conn does not exist in the current context.
{
conn.Open();
///...1st Query
QueryTwoFields("SELECT fullname,online FROM member WHERE active = '1' ORDER BY online DESC",listMember,listOnline);
//...2nd query
//QueryTwoFields("your new Select Statement", otherList, otherList);
}
}
You don't have to close connection every time you execute one query rarher than close the sqlreader assigned to that connection. Finally when all of your queries have been executed you close the connection. Consider also the use of using:
You cal also define a method for execution your Query in order for your code not to be repetive:
public void QueryTwoFields(string s, List<string> S1, List<string> S2)
///Select into List S1 and List S2 from Database (2 fields)
{
try
{
MySqlCommand cmd = conn.CreateCommand();
cmd.CommandType = CommandType.Text;
string command = s;
cmd.CommandText = command;
MySqlDataReader sqlreader = cmd.ExecuteReader();
while (sqlreader.Read())
{
S1.Add(sqlreader[0].ToString());
S2.Add(sqlreader[1].ToString());
}
sqlreader.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private void button1_Click(object sender, EventArgs e)
{
if(listView1.Items.Count > 1)
{
listView1.Items.Clear();
}
var listMember = new List<string>{};
var listOnline = new List<string>{};
// SQL PART //
using (conn)
{
conn.Open();
///...1st Query
QueryTwoFields("SELECT fullname,online FROM member WHERE active = '1' ORDER BY online DESC",listmember,listonline)
//...2nd query
QueryTwoFields("your new Select Statement",myOtherList1,myOtherlist2)
....
}
}
EDIT :
Take in mind you cant define QueryTwoFields method inside button handler. You must define it outside (see code above).
Also Define your connection data in the start of the programm:
namespace MyProject
{
/// <summary>
/// Defiine your connectionstring and connection
/// </summary>
///
public partial class Form1 : Form
{ public static string connString = "Server=10*****;Port=3306;Database=e***;Uid=e***;password=********************;";
MySqlConnection conn = new MySqlConnection(connString);
.........
Datatables are fantastic
Using a data table is a nice way to do both read and write. And it comes with the luxury of eveything you can do with a datatable - like asssigning it directly to a datagrid control, sorting, selecting and deleting while disconnected.
The sample below assumes a MySqlConnection conection property managed by calls to your own OpenConnection() and CloseConnection() methods not shown.
Simple datatable read demo:
public DataTable Select(string query = "")
{
//Typical sql: "SELECT * FROM motorparameter"
DataTable dt = new DataTable();
//Open connection
if (this.OpenConnection() == true)
{
//Create Command
MySqlCommand cmd = new MySqlCommand(query, connection);
//Create a data reader and Execute the command
MySqlDataReader dataReader = cmd.ExecuteReader();
dt.Load(dataReader);
//close Data Reader
dataReader.Close();
//close Connection
this.CloseConnection();
//return data table
return dt;
}
else
{
return dt;
}
}
In case of writing back the datatable to the database - supply the SQL you used in the read (or would have used to read to the data table):
public void Save(DataTable dt, string DataTableSqlSelect)
{
//Typically "SELECT * FROM motorparameter"
string query = DataTableSqlSelect;
//Open connection
if (this.OpenConnection() == true)
{
//Create Command
MySqlCommand mySqlCmd = new MySqlCommand(query, connection);
MySqlDataAdapter adapter = new MySqlDataAdapter(mySqlCmd);
MySqlCommandBuilder myCB = new MySqlCommandBuilder(adapter);
adapter.UpdateCommand = myCB.GetUpdateCommand();
adapter.Update(dt);
//close Connection
this.CloseConnection();
}
else
{
}
}
The neat thing the datatable is extremely flexible. You can run your own selects against the table once it contains data and before writing back you can set or reset what rows needs updating and by default the datatable keeps track of what rows you update in the table. Do not forget primary key column(s) for all tables in the db.
For multiple queries consider if possible using a join between the database tables or same table if data related or use a UNION sql syntax if column count and type of data is the same. You can allways "create" your extra column in the select to differ what data comes from what part of the UNION.
Also consider using CASE WHEN sql syntax to conditionally select data from different sources.
I am writing a small XAML/C#/MySQL database and wanted to create a query that accepts parameters. However, the test query that I am setting up fails when I try to create it
var con = new MySqlConnection(ClsVariables.StrDb);
con.Open();
var command = new MySqlCommand("", con);
command =
new MySqlCommand("Create View r2_Add_Edit_View as SELECT era.contact_id, era.n_family FROM era WHERE era.contact_id = #ContactID", con) command.ExecuteNonQuery();
con.Close();
When I change the #ContactID to a specific number - it works fine.
After that I will need to create a recordset, and pass the parameter to it (but I can ask that in a secondary question).
Thanks as always.
When I change the #ContactID to a specific number - it works fine.
Well, you don't pass the parameter, so just add it to your command:
public class MySqlConnector
{
private readonly string _connString;
public MySqlConnector(string connString)
{
_connString = connString;
}
private MySqlCommand _command;
const string Sql = "Create View r2_Add_Edit_View as SELECT era.contact_id, era.n_family FROM era WHERE era.contact_id = #ContactID";
public void CreateView(int contactId)
{
if(_command == null)
{
_command = new MySqlCommand();
_command.CommandText = Sql;
_command.Connection = _connString;
}
_command.Parameters.AddWithValue("#ContactID", contactId);
_command.ExecuteNonQuery();
_command.Close();
}
}
Try to use Command AddParameters method.
command.Parameters.Add("#ContactID", SqlDbType.Int);
command.Parameters["#ContactID"].Value = value;
Don't ask me why, but I want put in an sqlCommand object something like this:
sqlConnection a = new sqlConection(...);
sqlCommand b = new sqlCommand("EXEC storedProcedure()", a);
sqlDataAdapter c = new sqlDataAdapter(b);
DataTable d = new DataTable();
c.Fill(d);
So, when the stored procedure makes an insert the row is successfully added but however the code throws an Exception.
I know exist an sqlCommand.CommandType specifically for stored procedures but my architecture need it made in this way.
set the adapter "SelectCommand" property instead
var cmd = new SqlCommand("EXEC storedProcedure()", a);
cmd.CommandType = CommandType.StoredProcedure; //set command property
//..
var adapter = new SqlDataAdapter();
adapter.SelectCommand = cmd; //set adapter command for select query
and your command type must be CommandType.StoredProcedure to exec SP and your architecture don't need this? simply ask him for a good reason.
Your SQL syntax is off.
From http://technet.microsoft.com/en-us/library/ms188332.aspx :
USE AdventureWorks2012;
GO
DECLARE #CheckDate datetime;
SET #CheckDate = GETDATE();
EXEC dbo.uspGetWhereUsedProductID 819, #CheckDate;
GO
So your code should be:
new sqlCommand("EXEC storedProcedure", a);
While there are many ways to do the same thing, there are some things that work best when you do them the way the framework suggests.
In this case there are several things that can happen when you run the stored procedure, depending on which procedure it is. It might return a set of row, or several sets of rows, or nothing at all. There are already things we can do to handle all those situations, courtesy of the .NET framework.
Here's some extension code I've used in the past for any SP that is returning one or more rowsets:
public static DataSet ExecuteStoredProcedure(this SqlConnection connection, string SPName, params object[] parameters)
{
using (var cmd = connection.CreateCommand())
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = SPName;
cmd.CommandTimeout = 60;
if (connection.State != ConnectionState.Open)
connection.Open();
SqlCommandBuilder.DeriveParameters(cmd);
int index = 1;
foreach (object p in parameters)
{
if (index >= cmd.Parameters.Count)
break;
cmd.Parameters[index++].Value = (p == null ? DBNull.Value : p);
}
using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
{
DataSet res = new DataSet();
adapter.Fill(res);
return res;
}
}
}
Handling non-rowset return values and output parameters takes a bit more work, but this will do for your immediate needs:
var conn = new SqlConnection("some connection string");
DataSet ds = conn.ExecuteStoredProcedure("storedProcedure");
DataTable d = ds == null ? null : ds.Tables.Length < 1 ? null : ds.Tables[0];
This is a question from an experienced beginner!
Using ASP.NET 4 C# AND SQL server,
I have a connection string in web.config to myDatabase named "myCS".
I have a database named myDB.
I have a table named myTable with a primary key named myPK
What are the NECESSARY lines of code behind (minimal code) to create a SQL connection, then select from myTable where myPK=="simpleText"
it will probably include:
sqlconnection conn = new sqlconnection(??? myCS)
string SQLcommand = select * from myDB.myTable where myPK==myTestString;
sqlCommand command = new SqlCommand(SQL,conn);
conn.Open();
booleanFlag = ????
conn.Close();
conn.Dispose();
then
If ( theAnswer != NULL ) // or (if flag)
{
Response.Redirect("Page1.aspx");
}
else
{
Response.Redirect("Page2.aspx");
}
Here is a limited simple tutorial:
First, you want to have a class to do the hard work for you, then you will use it with ease.
First, you have to crate the connection string in your web.config file and name it.
Here it is named DatabaseConnectionString, but you may named it myCS as required in the question.
Now, in App_Code create a new class file and name it SqlComm (this is just an example name) like:
using System;
using System.Data;
using System.Data.SqlClient;
using System.Web;
public class SqlComm
{
// this is a shortcut for your connection string
static string DatabaseConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["dbConStr"].ConnectionString;
// this is for just executing sql command with no value to return
public static void SqlExecute(string sql)
{
using (SqlConnection conn = new SqlConnection(DatabaseConnectionString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Connection.Open();
cmd.ExecuteNonQuery();
}
}
// with this you will be able to return a value
public static object SqlReturn(string sql)
{
using (SqlConnection conn = new SqlConnection(DatabaseConnectionString))
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
object result = (object)cmd.ExecuteScalar();
return result;
}
}
// with this you can retrieve an entire table or part of it
public static DataTable SqlDataTable(string sql)
{
using (SqlConnection conn = new SqlConnection(DatabaseConnectionString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Connection.Open();
DataTable TempTable = new DataTable();
TempTable.Load(cmd.ExecuteReader());
return TempTable;
}
}
// sooner or later you will probably use stored procedures.
// you can use this in order to execute a stored procedure with 1 parameter
// it will work for returning a value or just executing with no returns
public static object SqlStoredProcedure1Param(string StoredProcedure, string PrmName1, object Param1)
{
using (SqlConnection conn = new SqlConnection(DatabaseConnectionString))
{
SqlCommand cmd = new SqlCommand(StoredProcedure, conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(new SqlParameter(PrmName1, Param1.ToString()));
cmd.Connection.Open();
object obj = new object();
obj = cmd.ExecuteScalar();
return obj;
}
}
}
Okay, this only a class, and now you should know how to use it:
If you wish to execute a command like delete, insert, update etc. use this:
SqlComm.SqlExecute("TRUNCATE TABLE Table1");
but if you need to retrieve a specific value from the database use this:
int myRequiredScalar = 0;
object obj = new object();
obj = SqlComm.SqlReturn("SELECT TOP 1 Col1 FROM Table1");
if (obj != null) myRequiredScalar = (int)obj;
You can retrieve a bunch of rows from the database this way (others like other ways)
This is relevant to your sepecific question
int Col1Value = 0;
DataTable dt = new DataTable();
dt = SqlComm.SqlDataTable("SELECT * FROM myTable WHERE myPK='simpleText'");
if (dt.Rows.Count == 0)
{
// do something if the query return no rows
// you may insert the relevant redirection you asked for
}
else
{
// Get the value of Col1 in the 3rd row (0 is the first row)
Col1Value = (int)dt.Rows[2]["Col1"];
// or just make the other redirection from your question
}
If you need to execute a stored procedure with or without returning a value back this is the way to do that (in this example there are no returning value)
SqlComm.SqlStoredProcedure1Param("TheStoredProcedureName", "TheParameterName", TheParameterValue);
Again, for your specific question return the table using the SqlDataTable , and redirect if dt.Rows.Count >0
Have fun.
There are many ways: LINQ, SqlDataReader, SQLDataAdapter, according to what you want to read (single value, datatable ...), so here is an example:
using (SqlConnection con = new SqlConnection("SomeConnectionString"))
{
var cmd = new SqlCommand("select from myTable where myPK==N'"+ simpleText+ "'",con);
cmd.Connection.Open();
var sqlReader = cmd.ExecuteReader();
while(sqlReader.Read())
{
//Fill some data like : string result = sqlReader("SomeFieldName");
}
sqlReader.Close();
cmd.Connection.Close();
cmd.Dispose();
}