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Best Practice: Convert LINQ Query result to a DataTable without looping
(5 answers)
Closed 8 years ago.
How can I convert the result of a LINQ query where I select some columns of a DataTable to a DataTable again?
DataTable dtN = new DataTable();
dtN.Columns.Add("Id");
dtN.Columns.Add("Name");
dtN.AcceptChanges();
for (int i = 1; i <= 10; i++)
{
DataRow dr = dtN.NewRow();
dr["Id"] = i;
dr["Name"] = "A"+i.ToString();
dtN.Rows.Add(dr);
dtN.AcceptChanges();
}
var data = from r in dtN.AsEnumerable()
select new { Name = r["Name"].ToString() };
//this line is giving error because CopyToDatatable is not available
DataTable dt = data.CopyToDataTable();
DataTable dtN = new DataTable();
dtN.Columns.Add("Id");
dtN.Columns.Add("Name");
dtN.AcceptChanges();
for (int i = 1; i <= 10; i++)
{
DataRow dr = dtN.NewRow();
dr["Id"] = i;
dr["Name"] = "A" + i.ToString();
dtN.Rows.Add(dr);
dtN.AcceptChanges();
}
var data = from r in dtN.AsEnumerable()
select new { Name = r["Name"].ToString() };
DataTable dt = new DataTable();
dt.Columns.Add("Name");
foreach(var s in data)
{
DataRow dr = dt.NewRow();
dr["Name"] = s.Name;
dt.Rows.Add(dr);
dt.AcceptChanges();
}
//DataTable dt = data.CopyToDataTable();
EDIT :
CopyToDataTable() is only available on IEnumerable<T> where T is or derives from DataRow.
So in your first case var data=from r in dtN.AsEnumerable() select r;
CopyToDataTable() is available because your query returns an IEnumerable<'DataRow> .
But in the second case var data = from r in dtN.AsEnumerable() select new { Name = r["Name"].ToString() };
you are returning an anonymous type.
Anonymous types don't carry the extension method for CopyToDataTable().
If you wish to convert a non-datatable-derived T to a datatable, MSDN has a sample class that reflects out any type and performs the conversion .Please Read this link
If you have a DataTable with a lot of columns:
var dt = new DataTable();
dt.Columns.Add("Foo", typeof(string));
dt.Columns.Add("Name", typeof(string));
dt.Columns.Add("Bar", typeof(int));
dt.Rows.Add(new object[]{"Foo", "Max", 555});
dt.Rows.Add(new object[]{"Blub", "Marry", 123});
dt.Rows.Add(new object[]{"Bla", "Mac", 999});
but you're only interested in a DataTable in one or some of the columns, but not all, you can simply use a DataView:
var nameOnlyTable = new DataView(dt).ToTable(false, new []{"Name"});
No need for LINQ.
Related
I have the following piece of code.
dt3 = new System.Data.DataTable();
foreach (DataRow sourceRow in dt2.Rows) {
DataRow destRow = dt3.NewRow();
destRow[0] = sourceRow[2];
dt3.Rows.Add(destRow);
}
And it is generating following error on line destRow[0] = sourceRow[2];
System.IndexOutOfRangeException: Cannot find column 0.
What am I doing wrong? Is there any way around it without declaring columns beforehand?
Here we create a "source" DataTable with 3 columns, and select two of those columns for the new DataTable:
DataTable srcDataTable = new DataTable();
srcDataTable.Columns.Add("Column A", typeof(string));
srcDataTable.Columns.Add("Column B", typeof(int));
srcDataTable.Columns.Add("Column C", typeof(int));
DataTable dstDataTable = new DataTable();
var desiredColumns = new[] { "Column A", "Column C" };
foreach (DataColumn col in srcDataTable.Columns)
{
if (desiredColumns.Contains(col.ColumnName))
{
dstDataTable.Columns.Add(col.ColumnName, col.DataType, col.Expression);
}
}
Now you can simply loop through the source table and copy the row data as you need it. Example for copying the rows:
foreach (DataRow srcRow in srcDataTable.Rows)
{
var newRow = dstDataTable.NewRow();
foreach (var columnName in desiredColumns)
{
newRow[columnName] = srcRow[columnName];
}
dstDataTable.Rows.Add(newRow);
}
Alternative approach using column numbers:
DataTable srcDataTable = new DataTable();
srcDataTable.Columns.Add("Column A", typeof(string));
srcDataTable.Columns.Add("Column B", typeof(int));
srcDataTable.Columns.Add("Column C", typeof(int));
DataTable dstDataTable = new DataTable();
var desiredColumns = new int[] { 0, 2 };
Dictionary<int, int> columnMap = new Dictionary<int, int>();
for (int colNum = 0; colNum < desiredColumns.Length; ++colNum)
{
columnMap[colNum] = desiredColumns[colNum];
dstDataTable.Columns.Add(srcDataTable.Columns[desiredColumns[colNum]].ColumnName, srcDataTable.Columns[desiredColumns[colNum]].DataType, srcDataTable.Columns[desiredColumns[colNum]].Expression);
}
foreach (DataRow srcRow in srcDataTable.Rows)
{
var newRow = dstDataTable.NewRow();
for (int colNum = 0; colNum < desiredColumns.Length; ++colNum)
{
newRow[colNum] = srcRow[columnMap[colNum]];
}
dstDataTable.Rows.Add(newRow);
}
This line dt3 = new System.Data.DataTable(); creates a new DataTable. But this table doesn't contain any columns yet. In fact, it's an empty table.
This line destRow[0] = sourceRow[2]; tries to set the value of the first column of your table. However, your table doesn't contain any columns yet. And this is what the error message is trying to tell you.
You have to create your column after creating the table. You can do it like this:
DataColumn idColumn = new DataColumn();
idColumn.DataType = System.Type.GetType("System.Int32");
idColumn.ColumnName = "id";
dt3.Columns.Add(idColumn);
Only after this, you will be able to put data into your first column.
Please take a look at this example in the Microsoft docs
What am I doing wrong?
Table dt3 has no column 0, because you haven't added one
Is there any way around it without declaring columns beforehand?
Even though you don't necessarily know the column name or type of dt2's column 2 at compile time, you seem to know that you definitely want column 2 from dt2 to be column 0 of dt3, so make sure you add a column to dt3 that is the same type (and giving it the same name seems reasonable too) as column 2 of dt2:
dt3 = new System.Data.DataTable();
dt3.Columns.Add(dt2.Columns[2].ColumnName, dt2.Columns[2].DataType);
foreach (DataRow sourceRow in dt2.Rows) {
DataRow destRow = dt3.NewRow();
destRow[0] = sourceRow[2];
dt3.Rows.Add(destRow);
}
You can try to use Clone() method to copy structure/columns from source table to destination table:
var dt3 = dt2.Clone();
From the docs.
Here and Two Variable Store Two tables Data Now I want to Add these tables in to DataTable through Foreach Loop ?
var meterData = MeterTable(startDateTime, endDateTime);
var levelData = LevelTable(startDateTime, endDateTime);
var dataTable = new DataTable();
dataTable.Columns.Add("Meter", typeof(string));
dataTable.Columns.Add("Volume", typeof(int));
dataTable.Columns.Add("OpeningBalance", typeof(int));
dataTable.Columns.Add("IN", typeof(int));
dataTable.Columns.Add("Transfer", typeof(int));
dataTable.Columns.Add("OUT", typeof(int));
dataTable.Columns.Add("ClosingBalance", typeof(int));
// how Onward i have not any idea ?
If you want all columns from each table you can do this:
var newTable = new DataTable();
//Copy the meter table into your new table
newTable = meterData.Copy();
//Use .Merge to merge in the level table
newTable.Merge(levelData);
If you want to add new rows, you create a datarow and add it to the datatable:
// Create new DataRow objects and add to DataTable.
for(int i = 0; i < someNumberOfRows; i++)
{
row = newTable.NewRow();
row["column1"] = i;
row["column2"] = "item " + i.ToString();
newTable.Rows.Add(row);
}
If you need to use foreach, I'm assuming you want to iterate the rows in your 2 tables:
foreach(DataRow r in meterData.Rows)
{
row = newTable.NewRow();
row["someColumn"] = r["someColumn"];
row["someOtherColumn"] = r["someOtherColumn"];
newTable.Rows.Add(row);
}
you can add new row through foreach loop like this
var dataTable = new DataTable();
dataTable.Columns.Add("Meter", typeof(string));
dataTable.Columns.Add("Volume", typeof(int));
foreach (var items in Source) //source is the where you want to loop
{
DataRow row = dataTable.NewRow();
row["Meter"] = "meter";
//you can access value of source items through item.NameofTargetField like items.meter
row["Volume"] = 11;
dataTable.Rows.Add(row);
}
Why does SqlDataAdapter's Fill method not allow me to add a row with the same its own rows' value as appearance? I could not success to provide a row's value that appears at the same row with filled one in DataTable.
Check this out:
using (SqlDataAdapter a = new SqlDataAdapter("SELECT SIPNO, SERINO, TARIH FROM SNOHAREKETLER WHERE Cast(TARIH as DATE) BETWEEN '2015/03/19' AND '2015/03/20' AND (TEZNO = 'T23' OR TEZNO = 'T31') AND CIKTI is null", c))
{
// 3
// Use DataAdapter to fill DataTable
DataTable t = new DataTable();
a.Fill(t);
t.Columns.Add("MyColumn", typeof(string));
DataRow workRow;
int iGetCount = t.Rows.Count;
for (int i = 0; i <= iGetCount - 1; i++)
{
workRow = t.NewRow();
workRow["MyColumn"] = i;
t.Rows.Add(workRow);
}
// 4
// Render data onto the screen
dataGridView1.DataSource = t;
}
Here is the solution of my issue. I searched and consulted someone. My issue was trying to add a NewRow and this causes the issue.
DataTable t = new DataTable();
a.Fill(t);
DataColumn newCol = new DataColumn("NewColumn", typeof(string));
newCol.AllowDBNull = true;
t.Columns.Add(newCol);
foreach (DataRow row in t.Rows)
{
row["NewColumn"] = "With String";
}
dataGridView1.DataSource = t;
My Datatable 1 (dtOutput) Format (termid,faultid,faultdesc,faulttime,devicetype)
My Datatable 2 (dtOpenEvent) Format (termid,faultid)
I want to retrieve those values which are present in Datatable 2 but not in Datatable 1...based on two columns (termid,faultid) no table have primary keys.
I Searched on net and find code which return diff between two data table...
Now how can i retrieve column values from it ? either in another data table or in string variable
Code :-
DataTable dtOpenEvent;
dtOpenEvent = Generix.getOpenEvents(ref Connection);
DataTable dtOutput;
dtOutput = Generix.getFeedData(ref Connection);
var matched = from table1 in dtOpenEvent.AsEnumerable()
join table2 in dtOutput.AsEnumerable() on table1.Field<string>("ATM") equals table2.Field<string>("termid")
where table1.Field<int>("Event") == table2.Field<int>("faultid")
select table1;
var missing = from table1 in dtOpenEvent.AsEnumerable()
where !matched.Contains(table1)
select table1;
you can remove all of the columns in dt1 and then do except.
like this:
var diff =dt2.AsEnumerable().Except(dt1.AsEnumerable(), DataRowComparer.Default);
full example:
DataTable dt1 = new DataTable();
DataTable dt2 = new DataTable();
dt1.Columns.Add("termid", typeof(Int32));
dt1.Columns.Add("faultid", typeof(Int32));
dt1.Columns.Add("faultdesc");
dt2.Columns.Add("termid", typeof(Int32));
dt2.Columns.Add("faultid", typeof(Int32));
dt1.Rows.Add(1,2,"desc");
dt1.Rows.Add(3, 4, "desc");
dt1.Rows.Add(5, 6, "desc");
dt2.Rows.Add(1, 2);
dt2.Rows.Add(3, 4);
dt2.Rows.Add(7, 8);
dt1.Columns.Remove("faultdesc");
var diff =dt2.AsEnumerable().Except(dt1.AsEnumerable(), DataRowComparer.Default);
foreach (var row in diff)
{
Console.WriteLine(row["termid"] + " " + row["faultid"]); //prints 7 8
}
or instead of removing columns you can select them through linq or dataview like this:
var view = new DataView(dt1);
DataTable dt3 = view.ToTable(true, "termid", "faultid");
modified example:
DataTable dt1 = new DataTable();
DataTable dt2 = new DataTable();
dt1.Columns.Add("termid", typeof(Int32));
dt1.Columns.Add("faultid", typeof(Int32));
dt1.Columns.Add("faultdesc");
dt2.Columns.Add("termid", typeof(Int32));
dt2.Columns.Add("faultid", typeof(Int32));
dt1.Rows.Add(1,2,"desc");
dt1.Rows.Add(3, 4, "desc");
dt1.Rows.Add(5, 6, "desc");
dt2.Rows.Add(1, 2);
dt2.Rows.Add(3, 4);
dt2.Rows.Add(7, 8);
var view = new DataView(dt1);
DataTable dt3 = view.ToTable(true, "termid", "faultid");
var diff =dt2.AsEnumerable().Except(dt3.AsEnumerable(), DataRowComparer.Default);
foreach (var row in diff)
{
Console.WriteLine(row["termid"] + " " + row["faultid"]);
}
As you said : I want to retrieve those values which are present in Datatable 2
but not in Datatable 1...based on two columns `(termid,faultid)`
Translation according to the context of question : You have two tables dtOutput and dtOpenEvent. You want to get values of dtOutput in a third table such that no row of third table has same value with first two cells of any row of dtOpenEvent. Then here it is
DataTable dt3 = new DataTable();
dt3.Columns.Add("termid");
dt3.Columns.Add("faultid");
int nr = 0;
for (int i = 0; i < dtOutput.Rows.Count; i++)
{
bool found = false;
for (int j = 0; j < dtOpenEvent.Rows.Count; j++)
{
if (dtOutput.Rows[i][0] == dtOpenEvent.Rows[j][0]
&& dtOutput.Rows[i][1] == dtOpenEvent.Rows[j][1])
{
found = true;
break;
}
}
if (!found)
{
dt3.Rows.Add(dt3.NewRow());
dt3.Rows[nr][0] = dtOutput.Rows[i][0];
dt3.Rows[nr][1] = dtOutput.Rows[i][1];
nr++;
}
}
For Performance improvement I want to convert datatable to datareader. I can not do that through query. So is there any other way to do so?
I know this is old, but the answers here seem to have missed the point of the OPs question.
DataTables have a method called CreateDataReader which will allow you to convert a DataTable to a DbDataReader object. In this case a DataTableReader.
DataTable table = new DataTable();
//Fill table with data
//table = YourGetDataMethod();
DataTableReader reader = table.CreateDataReader();
I should point out that this will not increase performance since you should be using one or the other.
Here are some more resources on the matter:
DataReader Vs DataTable
Is datareader quicker than dataset when populating a datatable?
For example
public DataTable ConvertDataReaderToDataTable(SqlDataReader dataReader)
{
DataTable datatable = new DataTable();
DataTable schemaTable = dataReader.GetSchemaTable();
try
{
foreach (DataRow myRow in schemaTable.Rows)
{
DataColumn myDataColumn = new DataColumn();
myDataColumn.DataType = myRow.GetType();
myDataColumn.ColumnName = myRow[0].ToString();
datatable.Columns.Add(myDataColumn);
}
while (dataReader.Read())
{
DataRow myDataRow = datatable.NewRow();
for (int i = 0; i < schemaTable.Rows.Count; i++)
{
myDataRow[i] = dataReader[i].ToString();
}
datatable.Rows.Add(myDataRow);
myDataRow = null;
}
schemaTable = null;
return datatable;
}
catch (Exception ex)
{
Error.Log(ex.ToString());
return datatable;
}
}
Use DataTable constructor,
DataTable table = new DataTable();
//Fill table with data
DataTableReader reader = new DataTableReader(table);
Good Look!
public DataTable GetTable(IDataReader _reader)
{
DataTable dataTable1 = _reader.GetSchemaTable();
DataTable dataTable2 = new DataTable();
string[] arrayList = new string[dataTable1.Rows.Count];
for (int i = 0; i < dataTable1.Rows.Count; i++)
{
DataColumn dataColumn = new DataColumn();
if (!dataTable2.Columns.Contains(dataTable1.Rows[i]["ColumnName "].ToString()))
{
dataColumn.ColumnName = dataTable1.Rows[i]["ColumnName "].ToString();
dataColumn.Unique = Convert.ToBoolean(dataTable1.Rows[i]["IsUnique "]);
dataColumn.AllowDBNull = Convert.ToBoolean(dataTable1.Rows[i]["AllowDBNull "]);
dataColumn.ReadOnly = Convert.ToBoolean(dataTable1.Rows[i]["IsReadOnly "]);
dataColumn.DataType = (Type)dataTable1.Rows[i]["DataType "];
arrayList[i] = dataColumn.ColumnName;
dataTable2.Columns.Add(dataColumn);
}
}
dataTable2.BeginLoadData();
while (_reader.Read())
{
DataRow dataRow = dataTable2.NewRow();
for (int j = 0; j < arrayList.Length; j++)
{
dataRow[arrayList[j]] = _reader[arrayList[j]];
}
dataTable2.Rows.Add(dataRow);
}
_reader.Close();
dataTable2.EndLoadData();
return dataTable2;
}