So I have a DataTable which uses a "SELECT * FROM People WHERE ID = ?" you can understand that this will only retrieve one row as the ID is unique
I have casted it to a list:
List<DataTable> userInfo = (List<DataTable>)HttpContext.Current.Session["userDT"];
Now I am trying to do a foreach loop that would loop through each row and store the column into a session, this is what I have so far:
However I get an error:
Cannot convert type 'System.Data.DataTable' to 'System.Data.DataRow'
Does anyone know what I am doing wrong?
userInfo is a list of tables. You have to iterate through it, and for each table you can access that table's rows:
foreach (DataTable dt in userInfo)
{
foreach (DataColumn column in dt.Columns)
{
// if you want column names here is how you would get them
string columnName = column.ColumnName;
foreach (DataRow row in dt.Rows)
{
// if you want the values in the cells, here's where you get them
object value = row[column];
}
}
}
Related
I have a DataTable in C#, and I would like to loop through each row of a particular column with the title specified.
Below is my code snippet:
foreach (DataRow listing in dtAll.Rows)
{
//get the value of <ID> column for each row
int itemID = ["ID"].value;
}
May I know how can it be done? Thank you.
foreach (DataRow listing in dtAll.Rows)
{
int itemID = listing.Field<int>("ID");
}
but note comments above as a search would probably have saved you posting
Im new to DataSets and I am trying to get a specific column from a DataSet. I wrote this code
using (var dataset = new U2ZFDataSetTableAdapters.stationenTableAdapter())
{
var ds = new U2ZFDataSet();
dataset.Fill(ds.stationen);
var rows = ds.stationen.Select("pdvorhanden = 1");
foreach (DataRow row in rows)
{
foreach (DataColumn column in ds.stationen.Columns)
{
if(column.ColumnName == "Bezeichnung")
listOfStations.Add(row[column].ToString());
}
}
}
The code feels slow to me. Isnt there a better way to do this? How can I get a specific Colum from DataRow without iterating through every column of the row?
Access to the column via column name.
foreach (DataRow row in rows)
{
listOfStations.Add(row["Bezeichnung"].ToString());
}
https://msdn.microsoft.com/en-us/library/146h6tk5(v=vs.110).aspx
Ok guys, I thought this would be easier than it is.
public static DataRowCollection ToRows(this DataGridViewSelectedRowCollection Rows)
{
DataTable table = new DataTable();
foreach (DataColumn column in Rows[0].DataGridView.Columns)
{
table.Columns.Add(column);
}
foreach (DataGridViewRow row in Rows)
{
DataRow newRow = ((DataRowView)row.DataBoundItem).Row;
table.ImportRow(newRow);
}
return table.Rows;
}
I'm trying to get the columns of a row in a DataGridViewSelectedRowCollection. The code above throws an InvalidCast error on the table.Columns.Add(column) because it is trying to cast DataGridViewColumns to DataTable columns. I dont have access to the DataGridView because I am in a static method that Extends the DataGridViewSelectedRowCollection and do not have access to the DataGridView.
How can I cast the columns collection to a DataColumns object?
You can create an extension method to return the data rows behind selected rows of grid this way:
public static class DataGridViewExtensions
{
public static List<DataRow> ToDataRows(this DataGridViewSelectedRowCollection Rows)
{
if (Rows == null || Rows.Count == 0)
return null;
return Rows.Cast<DataGridViewRow>()
.Where(x => x.DataBoundItem is DataRowView)
.Select(x => ((DataRowView)(x.DataBoundItem)).Row).ToList();
}
}
Then to get values from a row variable of type DataRow, consider using these options:
row.ItemArray contains all column values
row[index] gets the value of a column by index
row["column name"] gets the value of column by column name
row.Table.Columns contains a list of columns of DataTable
I have a datatable has data like this format
........ IVR........
.........IVR........
.........IVR........
.........City1......
.........City1......
.........City1......
.........City2......
.........City2......
.........City2......
I want to take the last row of each value. in order words, the rows that are bold now
The challenge is that i wan these three rows in a datatable. I tried to search on internet but i didn't know what is the name of this feature. could you help me please
You can GroupBy() and then select last row with the help of the Last() method.
var result = from b in myDataTable.AsEnumerable()
group b by b.Field<string>("Your_Column_Name") into g
select g.Last();
DataTable filtered = myDataTable.Clone();
foreach(DataRow row in result)
{
filtered.ImportRow(row);
}
Clone clones the structure of the DataTable, including all DataTable schemas and constraints.
This can be implemented in a simple loop using a Dictionary to hold found rows:
var cRows = new Dictionary<string, DataRow>(StringComparer.InvariantCultureIgnoreCase);
foreach (DataRow oRow in oTable.Rows)
{
var sKey = oRow["KeyValue"].ToString();
if (!cRows.ContainsKey(sKey))
{
cRows.Add(sKey, oRow);
}
else
{
cRows[sKey] = oRow;
}
}
This approach will store the last row for each unique value in the column that you nominate.
To move the selected rows into a new DataTable:
var oNewTable = oTable.Clone();
foreach (var oRow in cRows.Values)
{
oNewTable.Rows.Add(oRow);
}
Clone just clones the structure of the current table, not the rows.
I want to move the data from a dataColumn to a specific column in my dataTable. I am not sure how to specify what column within my Datatable I want to add the datacolumn.
foreach (DataColumn col in dt.Columns)
{
dt1.Columns.Add(col);
}
I receive an exception Column 'X' already belongs to another DataTable.
You need to copy the properties like ColumnName and create new DataColumns:
foreach (DataColumn col in dt.Columns)
{
dt1.Columns.Add(col.ColumnName, col.DataType);
}
There's a reason for the ArgumentException when you add a DataColumn which already belongs to another DataTable. It would be very dangerous to allow that since a DataTable holds a reference to their columns and every column holds a reference to it's DataTable. If you would add a column to another table your code would blow sooner or later.
If you also want to copy the DataRows into the new table:
foreach (DataRow row in t1.Rows)
{
var r = t2.Rows.Add();
foreach (DataColumn col in t2.Columns)
{
r[col.ColumnName] = row[col.ColumnName];
}
}
You cannot add a DataColumn from another table, because it already has an association with it's original table and a DataColumn is passed by reference to the Add method because it's an Object. You'll have to copy it. Here's one way you can do that:
public static class DataColumnExtensions
{
public static DataColumn CopyTo(this DataColumn column, DataTable table)
{
DataColumn newColumn = new DataColumn(column.ColumnName, column.DataType, column.Expression, column.ColumnMapping);
newColumn.AllowDBNull = column.AllowDBNull;
newColumn.AutoIncrement = column.AutoIncrement;
newColumn.AutoIncrementSeed = column.AutoIncrementSeed;
newColumn.AutoIncrementStep = column.AutoIncrementStep;
newColumn.Caption = column.Caption;
newColumn.DateTimeMode = column.DateTimeMode;
newColumn.DefaultValue = column.DefaultValue;
newColumn.MaxLength = column.MaxLength;
newColumn.ReadOnly = column.ReadOnly;
newColumn.Unique = column.Unique;
table.Columns.Add(newColumn);
return newColumn;
}
public static DataColumn CopyColumnTo(this DataTable sourceTable, string columnName, DataTable destinationTable)
{
if (sourceTable.Columns.Contains(columnName))
{
return sourceTable.Columns[columnName].CopyTo(destinationTable);
}
else
{
throw new ArgumentException("The specified column does not exist", "columnName");
}
}
}
public class MyClass
{
public static void Main()
{
DataTable tableA = new DataTable("TableA");
tableA.Columns.Add("Column1", typeof(int));
tableA.Columns.Add("Column2", typeof(string));
DataTable tableB = new DataTable("TableB");
foreach (DataColumn column in tableA.Columns)
{
column.CopyTo(tableB);
}
}
}
Note that there is also an extension method that can be used to Copy individual columns by name, i.e. tableA.CopyColumnTo("Column1", tableB);.
Then you can copy the data like this if the new table is an exact copy of the original:
foreach (DataRow row in tableA.Rows)
{
tableB.Rows.Add(row.ItemArray);
}
Or in a way similar to the second piece of code in Tim Schmelter's answer if it is not an exact copy. I would, however, recommend some error checking if you aren't copying all the columns into the new table:
foreach (DataRow souceRow in sourceTable.Rows)
{
DataRow destinationRow = destinationTable.Rows.Add();
foreach (DataColumn destinationColumn in destinationTable.Columns)
{
string columnName = destinationColumn.ColumnName;
if (sourceTable.Columns.Contains(columnName))
{
destinationRow[columnName] = sourceRow[columnName];
}
}
}
this is a normal behavior, if you're adding the same column to more than one DataTable ArgumentException will be thrown.
see documentation here:
http://msdn.microsoft.com/en-us/library/55b10992.aspx
you can create a new column same as the one you already added to the original table and add it to the new table.
Table data is organized by row, then by column. You can't (that I know of) add a column of data in one shot. You will need to add the column definition to the second table and add the data to it separately.
Since your original code looped through all columns, you may be better off copying the original datatable using DataTable.Copy() and deleting what you don't want.