there is no error just a clarification
I am trying to insert into a table called "Test" which has one column, a primary key called "id". I am new to using databases in visual studio and think there is something wrong with my insert syntax since all other functions work fine. is the general layout like this?
using (SqlCommand command = new SqlCommand("INSERT INTO Test (id) VALUES(1)", conn))
overall code looks like this:
class Program
{
static void Main(string[] args)
{
string connection =
"Data Source=.\\SQLEXPRESS;" +
"User Instance=true;" +
"Integrated Security=true;" +
"AttachDbFilename=|DataDirectory|HaythamService.mdf;";
try
{
using (SqlConnection conn = new SqlConnection(connection))
{
conn.Open();
using (SqlCommand command = new SqlCommand("INSERT INTO Test (id) VALUES(1)", conn))
{
command.ExecuteNonQuery();
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
for (int i = 0; i < reader.FieldCount; i++)
{
Console.WriteLine(reader.GetValue(i));
}
Console.WriteLine();
Console.Read();
}
}
}
conn.Close();
}
}
catch (Exception ex)
{
}
}
}
First of all: swallowing the exception will not help. Remove the try-catch-block and let your application run into the error - then you'll see what the problem is.
Secondly: You're executing the INSERT command using ExecuteNonQuery and right after that try to read from it using an SqlDataReader? What kind of output do you expect from that?
Probably, if ID is a primary key column, that will also be the cause of a primary key violation error, because actually you're executing the same insert twice using the same value - and this is not allowed for a primary key.
To put it short: Create a second command you ExecuteReader. The command should read SELECT * FROM Test.
Thirdly: Do use the SqlConnectionStringBuilder class to create your connection string instead of hardcoding it. This will help you against invalid connection strings.
Related
i want to delete data in my database and using this code but its now working
private static void DeletePreviousRecord()
{
string connectionString = "Data Source=ABDULLAH\\ABDULLAHZAFAR;Initial Catalog=FoodHunt;Integrated Security=True";
using (SqlConnection con = new SqlConnection(connectionString))
{
using (SqlCommand cmd = new SqlCommand("Delete From RestaurantsMenu", con))
{
try
{
cmd.CommandType = CommandType.StoredProcedure;
con.Open();
var result = cmd.ExecuteNonQuery();
con.Close();
}
catch (Exception ex)
{ }
}
}
}
i tried this but this is not working, how can i do that, any suggestion?
Setting the CommandType to StoredProcedure when you clearly use a sql text directly cannot do any good at your code.
Remove that line because the default is CommandType.Text (and this is correct for your command)
But as stated in the comment above.
If you catch the exception, at least write in some log or display at
video what the error message is
If you don't add a WHERE clause at your sql statement, you delete
everything in the table (Probably you are lucky that this code has
not worked)
Looking at your comment below, if you want to delete every record (and reset the Identity column if any) a faster approach is
using (SqlCommand cmd = new SqlCommand("TRUNCATE TABLE RestaurantsMenu", con))
For a quick reading about the difference between TRUNCATE and DELETE look at this article
As I can read from SQLite FAQ it supports multiple processes reading (SELECT) and only one process writing (INSERT, UPDATE, DELETE) database at any moment in time:
SQLite uses reader/writer locks to control access to the database.
When any process wants to write, it must lock the entire database file
for the duration of its update. But that normally only takes a few
milliseconds. Other processes just wait on the writer to finish then
continue about their business
I'm using System.Data.SQLite adapter via c#.
Could someone expalin me plz, how exactly this process is going on?
Will this process work automatically and writing SQLiteCommand will simply wait if there is another writing SQLiteCommand already executing over the same database?
Or maybe it will throw an exception? What kind of it?
Sorry but I found no information about this mechanics :)
Thank you.
UPDATE:
I've found post saying that exception will be raised with a specific errorcode
Is that statement correct?
I've investigated it by myself:
I created a sample SQLite database c:\123.db with one table Categories containing two fields: ID (uniqueidentifier) and Name (nvarchar).
I then wrote some multi-thread code to emulate multiple write access to the database (don't forget to add a System.Data.SQLite reference to your project if you use this code):
using System;
using System.Data.SQLite;
using System.Threading.Tasks;
namespace SQLiteTest
{
class Program
{
static void Main(string[] args)
{
var tasks = new Task[100];
for (int i = 0; i < 100; i++)
{
tasks[i] = new Task(new Program().WriteToDB);
tasks[i].Start();
}
foreach (var task in tasks)
task.Wait();
}
public void WriteToDB()
{
try
{
using (SQLiteConnection myconnection = new SQLiteConnection(#"Data Source=c:\123.db"))
{
myconnection.Open();
using (SQLiteTransaction mytransaction = myconnection.BeginTransaction())
{
using (SQLiteCommand mycommand = new SQLiteCommand(myconnection))
{
Guid id = Guid.NewGuid();
mycommand.CommandText = "INSERT INTO Categories(ID, Name) VALUES ('" + id.ToString() + "', '111')";
mycommand.ExecuteNonQuery();
mycommand.CommandText = "UPDATE Categories SET Name='222' WHERE ID='" + id.ToString() + "'";
mycommand.ExecuteNonQuery();
mycommand.CommandText = "DELETE FROM Categories WHERE ID='" + id.ToString() + "'";
mycommand.ExecuteNonQuery();
}
mytransaction.Commit();
}
}
}
catch (SQLiteException ex)
{
if (ex.ReturnCode == SQLiteErrorCode.Busy)
Console.WriteLine("Database is locked by another process!");
}
}
}
}
The result on my Core2Duo E7500 is that Exception is never raised!
Looks like SQLite is optimised enough for my needs (locking/unlocking is really fast and normally only takes a few milliseconds as SQLite FAQ tells us) - Great!
Note that there is no need to retrieve an integer ErrorCode for an SQLiteException - you can use a special enum ReturnCode field instead. All codes are described here.
Hope this information will help somebody.
I have read TONS of tutorials, articles and whatever regarding my issue and honestly, due to my lack of experience I can't twist my fingers around this one so I hope some of you guys can help me out :)
I am working on a project (simply to learn how to program so it's probably very basic), but I have this "News" page where I can update and delete data using a GridView.
Now I would like to INSERT something into my database using 3 textboxes and 1 submit button.
I have 3 rows that has to be inserted:
Headline
Date
Content/the news itself.
Which are stored under NyhedTB from the connectionstring: BoligStjernenConnectionString
My query looks like this:
INSERT INTO [NyhedTB] ([NyhedDato], [NyhedTitel], [NyhedTekst])
VALUES (#NyhedDato, #NyhedTitel, #NyhedTekst)
I read on the internet that this code should do the magic for me (I will have to insert my own values ofc.):
static void Insert()
{
try
{
string connectionString =
"server=.;" +
"initial catalog=employee;" +
"user id=sa;" +
"password=sa123";
using (SqlConnection conn =
new SqlConnection(connectionString))
{
conn.Open();
using (SqlCommand cmd =
new SqlCommand("INSERT INTO EmployeeDetails VALUES(" +
"#Id, #Name, #Address)", conn))
{
cmd.Parameters.AddWithValue("#Id", 1);
cmd.Parameters.AddWithValue("#Name", "Amal Hashim");
cmd.Parameters.AddWithValue("#Address", "Bangalore");
int rows = cmd.ExecuteNonQuery();
//rows number of record got inserted
}
}
}
catch (SqlException ex)
{
//Log exception
//Display Error message
}
}
I looked at this code and thought it should be easy enough but really, I can't figure it out.
Here is some advice to get you going, learning programming is a lot of
trial and error.
Start off basic, litrally put three textboxes on a form/page and a
button.
Double click the button to go the code-behind and view the buttons
click event.
Paste in the body of code included with your question (everything in the try-catch).
Put a break-point on the Public Void Button_Click line of code and press F11 to
step through the code.
"one thing is having the code-behind working but how to make the buttons and textboxes working is still a misery"*
Put the textbox as the value rather than your hardcoded values:
cmd.Parameters.AddWithValue("#Address", textBox1.Text);
You also should not insert the Id value, instead modify the EmployeeDetails table and set the ID column to in the properties set Identity Specification (IS Identity) = True. Then right click the ID column and set Primary Key.
Post any error messages you encounter here and when you do get get it working, an additional exercise (that will be very valuable for you) would use a database stored procedure rather than ad-hoc SQL, to safe-guard against sql-injection attacks.
I'm assuming you have SQL Server installed and have a 'employee' database with a table called EmployeeDetails.
protected void GvManualShows_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
//label lbl = (label)e.Row.FindControl("lblHidden");
if (e.Row.Cells[14].Text == "Y")
{
// CheckBox cb = (CheckBox)e.Row.FindControl("chk");
CheckBox chk = (CheckBox)e.Row.Cells[0].FindControl("chkBox");
chk.Checked = true;
}
}
}
It's fairly simple. You just have to modify the connection string, the query and its parameters:
private void button1_Click(object sender, EventArgs e)
{
try
{
string connectionString =
"server=SQLServer;" + // SQLServer is your SQL server machine
"initial catalog=employee;" + // employee is your database
"user id=sa;" + // sa is the login to connect the database
"password=sa123"; // sa123 is the password of the login
using (SqlConnection conn =
new SqlConnection(connectionString))
{
conn.Open();
using (SqlCommand cmd = new SqlCommand(
"INSERT INTO [NyhedTB] ([NyhedDato], [NyhedTitel], [NyhedTekst]) " +
"VALUES (#NyhedDato, #NyhedTitel, #NyhedTekst)", conn))
{
cmd.Parameters.AddWithValue("#NyhedDato", textBoxDate.Text);
cmd.Parameters.AddWithValue("#NyhedTitel", textBoxTitle.Text);
cmd.Parameters.AddWithValue("#NyhedTekst", textBoxBody.Text);
int rows = cmd.ExecuteNonQuery(); // Inserted rows number
}
}
}
catch (SqlException ex)
{
//Log exception
//Display Error message
}
}
I made changed example code with your requirements and added comments, hope it would be a bit clearer for you to understand whats going on:
static void Insert()
{
try
{
string connectionString =
"server=.;" +
"initial catalog=MyDatabaseName;" + //here you write database name where your NyhedTB table is
"user id=sa;" + //user name to connect to database
"password=sa123"; //password
using (SqlConnection conn = new SqlConnection(connectionString))
{
conn.Open();
using (SqlCommand cmd =
new SqlCommand("INSERT INTO NyhedTB (NyhedDato, NyhedTitel, NyhedTekst) VALUES (#NyhedDato, #NyhedTitel, #NyhedTekst)", conn))
{
//all "things" in your sql command what beggins with #
//means that it is parameter and you need to pass values for these parameters:
//For #NyhedDato parameter you set text from your textbox
cmd.Parameters.AddWithValue("#NyhedDato", txtDate.Text);
//For #NyhedTitel parameter you set text from title textbox
cmd.Parameters.AddWithValue("#NyhedTitel", txtTitle.Text);
//For #NyhedTekst parameter you set text from content textbox
cmd.Parameters.AddWithValue("#NyhedTekst", txtContent.Text);
//Execute insert command and get how many records was efected, in this case it should be rows = 1 because you inserting just one record
int rows = cmd.ExecuteNonQuery();
}
}
}
catch (SqlException ex)
{
//Log exception
//Display Error message
}
}
P.s. code not tested. And when you say
I have 3 rows that has to be inserted:
Headline
Date
Content/the news itself.
actually you mean you want to insert record with fields
I don't know much about exporting data using OLEDB, I figured the following:
using (OleDbConnection conn = new OleDbConnection(connString))
{
try
{
conn.Open();
foreach (T t in rows)
{
using( OleDbCommand oleDbCommand = new OleDbCommand(insertString, conn))
{
OleDbParameter param = new OleDbParameter(.., ..);
oleDbCommand.Parameters.Add(param);
//add more parameters
oleDbCommand.ExecuteNonQuery();
}
}
}
catch (Exception e)
{
//handle
}
}
At first, I didn't use the using statement for the OleDbCommand (i.e., I didn't dispose of the OleDbCommand). But in that case, a record locking file remained on the database even though I was finished exporting. WITH the (inner) Using statement however, exporting seems slower. Why? And how to get both the fast exporting and the removal of the record locking at the end of exporting?
Since you do not close the Connection, the ldb file remains present as you're still connected to the DB.
So, you should put a using statement around the connection-declaration (or close the connection in the finally block of your try statement [which is exactly what the using statement does nb).
using( var conn = new OleDbConnection (connectionstring) )
{
conn.Open();
using( cmd = conn.CreateCommand() )
{
cmd.Parameters.Add (..);
...
for( ... )
{
cmd.Parameters.Clear();
cmd.CommandText = "";
cmd.Parameters["#p_param"].Value = ...
cmd.ExecuteNonQuery();
}
}
}
With the using clause in the for-loop, you're disposing the OleDbCommand for every record that you're going to insert. However, you can re-use the OleDbCommand instance for every insert. (See code above).
Next to that, you should start a transaction explicitly. Since, when you do not do that, an implicit transaction will be created for each insert statement.
Also, by performing all the inserts inside one transaction, you'll be able to rollback all the changes (inserts) that you've done when you encounter an error.
(For instance, if inserting row nr 159 fails, you can rollback all the 158 inserts that you've done before).
When several fields in a MSAccess table need to be updated (For instance Salary=Salary*Factor, SomeNumber=GetMyBusinessRuleOn(SomeNumber) etc...),and the update should affect every record in a table, which technique would you use?
I have just started to implement this with DataSets, but got stuck (Updating and persisting dataset problem)
But maybe this isn't even the ideal way to handle this kind of batch update?
Note : the updates don't have to be on disconnected data first, so a dataset is not necessary.
UPDATE :
One command won't do, I need some kind of recordset or cursor to cycle through the records
I would just use a ODBCConnection/ODBCCommand and use a SQL Update query.
There is a JET Database driver that you should be able to use to establish a database connection to a MSAccess database using the ODBCConeection object.
string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\\PathTo\\Your_Database_Name.mdb; User Id=admin; Password=";
using (OdbcConnection connection =
new OdbcConnection(connectionString))
{
// Suppose you wanted to update the Salary column in a table
// called Employees
string sqlQuery = "UPDATE Employees SET Salary = Salary * Factor";
OdbcCommand command = new OdbcCommand(sqlQuery, connection);
try
{
connection.Open();
command.ExecuteNonQuery();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
// The connection is automatically closed when the
// code exits the using block.
}
You could use these websites to help you generate a connection string:
http://www.connectionstrings.com/
http://www.sqlstrings.com/
EDIT - Example for using a data reader to cycle through records in order to aply the business rule
I should note that the following example could be improved in certain ways (especially if the database driver supports parameterized queries). I only wanted to give a relatively simple example to illustrate the concept.
using (OdbcConnection connection =
new OdbcConnection(connectionString))
{
int someNumber;
int employeeID;
OdbcDataReader dr = null;
OdbcCommand selCmd = new OdbcCommand("SELECT EmployeeID, SomeNumber FROM Employees", connection);
OdbcCommand updateCmd = new OdbcCommand("", connection);
try
{
connection.Open();
dr = selCmd.ExecuteReader();
while(dr.Read())
{
employeeID = (int)dr[0];
someNumber = (int)dr[1];
updateCmd.CommandText = "UPDATE Employees SET SomeNumber= " + GetBusinessRule(someNumber) + " WHERE employeeID = " + employeeID;
updateCmd.ExecuteNonQuery();
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
finally
{
// Don't forget to close the reader when we're done
if(dr != null)
dr.Close();
}
// The connection is automatically closed when the
// code exits the using block.
}
Sounds like you just need an update statement:
http://msdn.microsoft.com/en-us/library/bb221186.aspx
You can use the OleDb Provider for this.