I'm trying to retrieve the names of the table from the local database I'm using.
This the code I've tried but it never goes through the foreach loop:
public void GetColumnNames()
{
SqlConnection con;
SqlDataAdapter adapter = new SqlDataAdapter();
DataSet ds = new DataSet();
con = new SqlConnection(Properties.Settings.Default.AlhusainSoundDBConnectionString);
List<string> colns = new List<string>();
try
{
con.Open();
}
catch (SqlException ex)
{
MessageBox.Show(ex.Message);
}
foreach (DataTable dt in ds.Tables)
{
colns.Add(dt.TableName);
Console.WriteLine(dt.TableName);
}
}
So could anyone please suggest me how to do that correctly
Regards
To get table names you need to use INFORMATION_SCHEMA
USE <your_database_name>
GO
SELECT * FROM INFORMATION_SCHEMA.TABLES
You haven't done anything except open a connection to the database. Your dataset has not been populated with any data. My approach would be to use a SqlCommand object to execute the following SQL Statement and populate a SqlDataReader
SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
So, the C# code might look something like this:
string sql = "SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES";
using (SqlConnection con = new SqlConnection(Properties.Settings.Default.AlhusainSoundDBConnectionString))
using (SqlCommand cmd = new SqlCommand(sql, con))
{
con.Open();
using (SqlDataReader dr = cmd.ExecuteReader())
{
while (dr.Read())
{
// do something with each table
string tableName= dr["TABLE_NAME"].ToString();
// OR
// string tableName = dr[0].ToString();
// OR
// string tableName = dr.GetString(0);
}
}
}
Related
This is probably a simple question but I am not experienced in C#.
I have 2 datatables, 1 is basically a copy of the other (like a table to review information). To set the values this is what I am doing now:
string attribute1 = "";
string attribute2 = "";
string attribute3 = "";
.....
DataTable result = new DataTable();
using (SqlConnection con = new SqlConnection("user id=user_id;password=pwd;server=serverstring;Trusted_Connection=yes;database=database;connection timeout=30"))
{
using (SqlCommand cmd = new SqlCommand("SELECT * FROM table1 WHERE parameter=#identifying_parameter", con))
{
cmd.Parameters.AddWithValue("#identifying_parameter", "example");
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
if (reader.Read())
{
attribute1 = Convert.ToString(reader["attribute1"]);
attribute2 = Convert.ToString(reader["attribute2"]);
attribute3 = Convert.ToString(reader["attribute3"]);
.....
}
con.Close();
}
}
using (SqlConnection con = new SqlConnection("user id=user_2;password=pwd;server=serverstring;Trusted_Connection=yes;database=database;connection timeout=30"))
{
using (SqlCommand cmd = new SqlCommand("INSERT INTO table2 (attribute1, attribute2, attribute3, ...) VALUES(#attribute1, #attribute2, #attribute3, ...)", con))
{
cmd.Parameters.AddWithValue("#attribute1", attribute1);
cmd.Parameters.AddWithValue("#attribute2", attribute2);
cmd.Parameters.AddWithValue("#attribute3", attribute3);
....
con.Open();
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(result);
con.Close();
da.Dispose();
}
}
Obviously I might have a lot of attributes, so is there a simpler way to set every attribute in the table to be equal in C#?
You can use INSERT..INTO..SELECT
DataTable result = new DataTable();
using (SqlConnection con = new SqlConnection("user id=user_2;password=pwd;server=serverstring;Trusted_Connection=yes;database=database;connection timeout=30"))
{
using (SqlCommand cmd = new SqlCommand(#"INSERT INTO table2 (attribute1, attribute2, attribute3, ...)
SELECT attribute1, attribute2, attribute3 ... FROM table1
WHERE parameter=#identifying_parameter
", con))
{
cmd.Parameters.AddWithValue("#identifying_parameter", "example");
con.Open();
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(result);
con.Close();
da.Dispose();
}
}
You can use * instead of specifying the column name, although which is not good practice..
In order to make a second Table identical (or "equivalent" as per your definition) to the first one (for certainty let's call it sourceTable), you can use SqlBulkCopy.WriteToServer Method (DataTable)(re: https://msdn.microsoft.com/en-us/library/ex21zs8x%28v=vs.110%29.aspx)
using (SqlConnection YourConnection= new SqlConnection(YourConnectionString))
{
YourConnection.Open();
using (SqlBulkCopy bulkCopy = new SqlBulkCopy(YourConnection))
{
bulkCopy.DestinationTableName = "dbo.YourDestinationTable";
try
{
// Write from the source to the destination.
bulkCopy.WriteToServer(sourceTable);
}
catch (Exception ex) { }
}
}
In order to get a sourceTable you can use the following code snippet:
DataTable sourceTable = SqlReadDB(YourConnString, "SELECT *")
private static DataTable SqlReadDB(string ConnString, string SQL)
{
DataTable _dt;
try
{
using (SqlConnection _connSql = new SqlConnection(ConnString))
{
using (SqlCommand _commandl = new SqlCommand(SQL, _connSql))
{
_commandSql.CommandType = CommandType.Text;
_connSql.Open();
using (SqlCeDataReader _dataReaderSql = _commandSql.ExecuteReader(CommandBehavior.CloseConnection))
{
_dt = new DataTable();
_dt.Load(_dataReaderSqlCe);
_dataReaderSql.Close();
}
}
_connSqlCe.Close();
return _dt;
}
}
catch { return null; }
}
}
Hope this may help.
I have the below code, which works, but is only reading the top row of the DB and then terminating. The array should hold 3 pieces of data, but it only holds one.
I think this is because it is not looping.
How do you say for the code to carry on running until it has no more data to read?
SqlConnection conn1 = new SqlConnection(ssConnectionString);
conn1.Open();
SqlCommand command1 = conn1.CreateCommand();
command1.CommandText = "SELECT FeedURL FROM [dbo].[Feeds]";
rssFeeds.Add(command1.ExecuteScalar());
conn1.Close();
By default ExecuteScalar() will only ever return one value. You would need to create a DataReader, and then loop through the results using command1.ExecuteReader()
conn1.Open();
string query = "select feedurl from [dbo].[feeds]";
DataSet DS = new DataSet();
SqlDataAdapter adapt = new SqlDataAdapter(query,conn1);
adapt.Fill(DS);
if (DS != null)
{
if (DS.Tables[0].rows.Count > 0 )
{
foreach(DataRow DR in DS.Tables[0].Rows)
{
string temp = DR['columnname'];
}
}
{
You can just use ExecuteReader for your problem. In this example that I took from MSDN is consuming the connection with using statement because SqlConnection class has some unmanaged resources. If you have more questions about using and Finalizers also check here.
How to use ExecuteReader, you can check here:
static void HasRows(SqlConnection connection)
{
using (connection)
{
SqlCommand command = new SqlCommand(
"SELECT CategoryID, CategoryName FROM Categories;",
connection);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
Console.WriteLine("{0}\t{1}", reader.GetInt32(0),
reader.GetString(1));
}
}
else
{
Console.WriteLine("No rows found.");
}
reader.Close();
}
}
Try this:
//method to make this code reusable
//the returned data set is accessible even if the underlying connection is closed
//NB: that means data's held in memory; so beware of your resource usage
public DataSet ExecuteSQLToDataSet(string ssConnectionString, string query, string name)
{
DataSet ds = new DataSet("Tables");
using (SqlConnection conn1 = new SqlConnection(ssConnectionString))
{
conn1.Open();
SqlDataAdapter sda = new SqlDataAdapter(query, objConn);
sda.FillSchema(ds, SchemaType.Source, name);
sda.Fill(ds, name);
} //using statement will close and dispose the connection for you
return ds;
}
//example usage
DataSet ds = ExecuteSQLToDataSet(ssConnectionString, "SELECT FeedURL FROM [dbo].[Feeds]", "Feeds"); //nb: name doesn't have to match table name; you can call it what you like; naming is useful if you wanted to add other result sets to the same data set
//DataTable tblFeeds = ds.Tables["Feeds"]; //if you want to access the above query by name
foreach (DataTable tbl in ds.Tables)
{
foreach (DataRow dr in tbl.Rows) //tblFeeds.Rows if you did that instead of looping through all tables
{
//Console.WriteLine(dr["FeedURL"].ToString()); //you can specify a named column
Console.WriteLine(dr[0].ToString()); //or just use the index
}
}
Console.WriteLine("Done");
Console.ReadLine();
More Detail: http://support.microsoft.com/kb/314145
I want to get the result from a query in my oracle database and put it in a gridview. Now my problem is, I have no idea how to output it in the gridview. I am using the gridview from the toolbox and my oracle connection is working. I also have the right SELECT query and I can output that in a listbox. I just have no idea how to do this in a gridview. I looked for it and I came across this: How to populate gridview with mysql? Although this doesn't help me.
How can I output it in a gridview so that it looks exactly the same as a normal table in the oracle database?
What should I use and how?
This is my code:
public void read()
{
try
{
var conn = new OracleConnection("")
conn.Open();
OracleCommand cmd = new OracleCommand("select * from t1", conn);
OracleDataReader reader = cmd.ExecuteReader();
DataTable dataTable = new DataTable();
while (reader.Read())
{
var column1 = reader["vermogen"];
column = (column1.ToString());
listBox1.Items.Add(column);
}
conn.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
To bind a DataTable to a DataGridView your code need simply to be changed to
public void read()
{
try
{
using(OracleConnection conn = new OracleConnection("....."))
using(OracleCommand cmd = new OracleCommand("select * from t1", conn))
{
conn.Open();
using(OracleDataReader reader = cmd.ExecuteReader())
{
DataTable dataTable = new DataTable();
dataTable.Load(reader);
dataGridView1.DataSource = dataTable;
}
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
}
The OracleDataReader could be passed to the Load method of the DataTable and then the table is ready to be bound to the DataGridView DataSource property. I have also added some using statement to ensure proper disposing of the disposable objects employed. (In particular the OracleConnection is very expensive to not close in case of exceptions)
You can use DataSet too:
public void read()
{
try
{
OracleConnection conn = new OracleConnection("");
OracleCommand cmd = new OracleCommand("select * from t1", conn);
conn.Open();
cmd.CommandType = CommandType.Text;
DataSet ds = new DataSet();
OracleDataAdapter da = new OracleDataAdapter();
da.SelectCommand = cmd;
da.Fill(ds);
dataGridView1.DataSource = ds.Tables[0];
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
}
First establish connection in case, you didnt establish globally by using connection string. Then use oleDbcommand for the oracle sql command you want to execute. In my case, it is 'select * from table_name' which would show all data from table to datagrid. I wrote this code in a button to display data on data grid.
{
OleDbConnection conn = new OleDbConnection("");
OleDbCommand cmd = new OleDbCommand("select * from table_name", conn);
{
conn.Open();
OleDbDataReader reader = cmd.ExecuteReader();
{
DataTable dataTable = new DataTable();
dataTable.Load(reader);
dataGridView1.DataSource = dataTable;
}
conn.Close();
}
}
I am new to SQL, In my project I am trying to fill the DataSet from the DataBase table and then inserting new rows in DataSet. After doing this, again I am filling the Database table with the DataSet data. Before filling I am clearing or deleting the Database table data. Well I achieved this by using the below code:
Database Table --> myTable
DataSet --> ds
OnButtonClick
string strQuery = "delete from [dbo].[myTable]"
SqlConnection conn = new SqlConnection(strConn);
SqlCommand cmd = new SqlCommand(strQuery, conn);
SqlCommand command;
SqlDataAdapter da = new SqlDataAdapter(cmd);
using (cmd)
{
using (conn)
{
conn.Open();
cmd.ExecuteNonQuery(); //deleting database table data
foreach (DataRow dr in ds.Tables[0].Rows) //Inserting new data into the Database table
{
command = new SqlCommand(InsertQuery, conn);
command.ExecuteNonQuery();
}
conn.Close();
}
}
The above code is working fine but when there is any exception in command sqlCommand then it is deleting the database table completely and not filling the DataSet. Any suggestions to modify this code? please help.
UPDATE:
string strQuery = "delete from [dbo].[myTable]";
using (SqlCommand cmd = new SqlCommand(strQuery, conn))
{
using (SqlCommand cmdReset = new SqlCommand("DBCC CHECKIDENT('myTable', RESEED, 0)", conn))
{
SqlDataAdapter da = new SqlDataAdapter(cmd);
conn.Open();
SqlTransaction sqlTransaction = conn.BeginTransaction();
cmd.Transaction = sqlTransaction;
try
{
cmd.ExecuteNonQuery(); //deleting database table data
cmdReset.ExecuteNonQuery(); //Resetting Identity of first column
foreach (DataRow dr in ds.Tables[0].Rows) //Inserting new data into the Database table
{
command = new SqlCommand(query.createDoctorRow(InsertQuery, conn);
command.ExecuteNonQuery();
}
sqlTransaction.Commit();
conn.Close();
}
catch (Exception e)
{
sqlTransaction.Rollback();
/*ERROR*/ throw;
}
}
}
ERROR --> "ExecuteNonQuery 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."
Use a transaction to run the sql
string strQuery = "delete from [dbo].[myTable]";
using (SqlConnection conn = new SqlConnection(strConn))
{
using (cmd = new SqlCommand(strQuery, conn))
{
SqlDataAdapter da = new SqlDataAdapter(cmd);
conn.Open();
SqlTransaction sqlTransaction = conn.BeginTransaction();
cmd.Transaction = sqlTransaction;
try
{
cmd.ExecuteNonQuery(); //deleting database table data
foreach (DataRow dr in ds.Tables[0].Rows) //Inserting new data into the Database table
{
command = new SqlCommand(InsertQuery, conn);
command.ExecuteNonQuery();
}
sqlTransaction.Commit();
conn.Close();
}
catch(Exception e)
{
sqlTransaction.Rollback();
throw;
}
}
}
Transactions form an all or nothing scenario. Either everything in the transaction works and is committed to the database, or the whole lot is cancelled as if nothing happened.
This example has a nice way of wrapping sql commands in a transaction scope. Basically if any exception is thrown during any of the row insert the delete query will fail as well.
In a nut shell you wrap everything inside a
using (TransactionScope scope = new TransactionScope())
{
using (SqlConnection connection1 = new SqlConnection(connectString1))
{
//enter your code here
}
}
Also you don't have to do an insert row by row you can use the SqlBulkCopy to do it more efficiently.
using (SqlConnection connection =new SqlConnection(connectionString))
{
connection.Open();
using (SqlBulkCopy bulkCopy = new SqlBulkCopy(connection))
{
bulkCopy.DestinationTableName = table.TableName;
bulkCopy.WriteToServer(table);
}
}
Why do I get this exception in my code? I restarted the server, changed ports, etc, but nothing is working.
What's wrong?
DataTable dt = new DataTable();
SqlConnection con = new SqlConnection("server=localhost;user=armin;password=root;");
con.Open();
SqlCommand result = new SqlCommand(
"SELECT userid FROM KDDData.dbo.userprofile order by userid", con);
SqlDataReader reader = result.ExecuteReader();
dt.Load(reader);
List<string> userids = new List<string>(dt.Rows.Count);
foreach (DataRow item in dt.Rows)
{
userids.Add(item.ItemArray[0].ToString().Trim());
}
con.Close();
con = new SqlConnection("server=localhost;user=armin;password=root;");
con.Open();
foreach (string user in userids)
{
DataTable temp = new DataTable();
SqlCommand result1 = new SqlCommand(
"select itemid from KDDTrain.dbo.train where userid=" + user, con);
SqlDataReader reader1 = result1.ExecuteReader();
if (!reader1.HasRows)
{
continue;
}
temp.Load(reader1);
}
The first query works fine, but the second doesn't. As you can see I even use some other SqlConnection but it still doesn't work.
Note:The database i'm working with has atleast 100 milion records,thought may be this would be a problem.
Something doesn't look right in your connection string
I always seen "server=localhost; user=armin;password=root" in connections strings for MySql not for SqlServer where instead I will use "Data Source=(LOCAL);Integrated Security=SSPI" or the INSTANCE name of SqlServer. Are you sure that the first query works?.
However I think you should use the appropriate using statement
DataTable dt = new DataTable();
using(SqlConnection con = new SqlConnection("server=localhost;user=armin;password=root;"))
{
using(SqlCommand result = new SqlCommand(
"SELECT userid FROM KDDData.dbo.userprofile order by userid", con))
{
con.Open();
using(SqlDataReader reader = result.ExecuteReader())
{
dt.Load(reader);
List<string> userids = new List<string>(dt.Rows.Count);
foreach (DataRow item in dt.Rows)
{
userids.Add(item.ItemArray[0].ToString().Trim());
}
}
DataTable temp = new DataTable();
foreach (string user in userids)
{
using(SqlCommand result1 = new SqlCommand(
"select itemid from KDDTrain.dbo.train where userid=" + user, con))
{
using(SqlDataReader reader1 = result1.ExecuteReader())
{
if (!reader1.HasRows) continue;
temp.Load(reader1);
}
}
}
}
Please insert this line
result1.CommandTimeout = 0;
befor this line in the second query
SqlDataReader reader1 = result1.ExecuteReader();
Dispose your reader after:
foreach (DataRow item in dt.Rows)
{
userids.Add(item.ItemArray[0].ToString().Trim());
}
...and also close the connection after temp.Load(reader1). Also close the reader1.
Instead of all this... the clean way is to use USING for initializng the readers and connection. :)