DataTable Intersection Operation - datatable

I have two datatables defined like this;
Dim db1, db2 As New DataTable
db1 and db2 hold results from different queries but the columns in both are exactly the same. I would like to create another datatable which consists of records that are in both db1 and db2. i.e I want the intersection of the two datatables. Is there an easy way to do this?
(The resultant datatable will be used to populate a gridview.)

You can try in this way.
// Declare Data Table and Data View
DataTable dt1 = new DataTable();
DataTable dt2 = new DataTable();
DataTable dt3 = new DataTable();
DataTable dtTemp = new DataTable();
DataView dv = new DataView();
dt1.Columns.Add("Col1");
dt1.Columns.Add("Col2");
dt1.Columns.Add("Col3");
dt2.Columns.Add("Col1");
dt2.Columns.Add("Col2");
dt2.Columns.Add("Col3");
// Initialize Data Table and Data View
dt1.Rows.Add("A", "B", "C"); // Testing data for data table 1; actual data will come from your query
dt1.Rows.Add("E", "F", "G"); // ==
dt2.Rows.Add("A", "B", "C");
dt2.Rows.Add("U", "V", "W");// Testing data for data table 2; actual data will come from your query
dt2.Rows.Add("X", "Y", "Z");// ==
// Merge Data Table into temporary Data Table
dtTemp = dt1; //Initialize dt1 value in to dtTemp
dtTemp.Merge(dt2);// Merge it with dt2 you will get the
// Use Data View to get disticnt values
dv = new DataView(dtTemp);
dt3 = dv.ToTable(true, "Col1", "Col2", "Col3");// Remember, it is for intersection not for union

If you are using VB.NET with LINQ you could do it like this:
Dim db3 = db1.Intersect(db2)
From there just use db3 to populate your GridView.

Related

How do you add your queried datatable results into a new datatable

Can someone please help me fill my queried results into the existing datatable or a new datatable
''dt is filled with data from a csv file.
Dim dataRows As DataRow() = dt.Select("[Calendar year TEXT] = '2020'")
dt.Clear() 'Clear the datatable
dt.Rows.Add(dataRows) 'Add the result to the existing datatable or a new databletable if possible ?
So I've figured it out.
The reason I need a new DataTable is that I need to use it again in its original form later.
I could not attach the DataRow collection to my display control which is why I needed a new DataTable with the filtered results.
Private Function FilterDataTable(ByVal strQuery As String, ByVal dtRaw As DataTable)
Dim dataRows As DataRow() = dtRaw.Select(strQuery)
Dim dtFiltered As DataTable
dtFiltered = dtRaw.Clone() 'This is very important.
For Each drow As DataRow In dataRows
dtFiltered.ImportRow(drow) 'Add each filtered row to new DataTable.
Next
Return dtFiltered
End Function
Your dt.select will return an array of Datarow pointing to the rows in the datatable dt. Your dt.clear then clears the datatable and so will empty the dataRows array leaving you nothing left.
I'm not clear exactly what you are trying to do. I'm guessing you have a table that you want to filter and then discard all rows that don't match, leaving you a datatable to work with.
If so, here's a few options:
Work with the datarow array directly rather than the datatable. Is there really any need to convert the rows back to a datatable?
Create a new datatable to add the rows to, but don't clear the original table:
Dim dt As New DataTable ' Assume this is your populated table
Dim dataRows As DataRow() = dt.Select("[Calendar year TEXT] = '2020'")
Dim dtResults As DataTable = dt.Clone()
For Each row As DataRow In dr
dtResults.ImportRow(row)
Next
bare in mind any changes you make to the rows in dtResults will also affect the rows in dt as they both contain the same data
Depending on the size of your table and whether or not you really want to discard non matching rows, you could just remove all rows that don't match then work with the result:
Dim i As Integer = dt.Rows.Count - 1
While i >= 0
If dt(i).Item("Calendar") <> "Your test here" Then dt.Rows.Remove(dt(i))
i -= 1
End While

Bind Objects To DataGridview and Reorder Column

I want to bind the object list to dataGridView.
Now i want the desired column to be the way i definde them. i.e., I want the objects to be order the way i want.
Like
var dataSource = linkItemListCommon.Select(x => new DataToBind { Select = x.Default, FileName = x.Text, CurrentDate = x.Date+" "+x.Time , PreviousDate = string.Empty, Size = x.Size }).ToList();
var filenamesList = new BindingList<DataToBind>(dataSource);
dgvDownLoadMaster.DataSource = filenamesList;
I want the datagrid columns to be in the order that i define.
Like here i expect them to be in order given below:
Select FileName CurrentDate PreviousDate Size
But the column list is appearing not as per my requirements.
How to Do that.Please help.
Create columns by hand and then you can order them easily. You can add columns trough designer and just set each column DataPropertyName to corresponding field.
Or you can create each column programmatically:
var col = new DataGridViewTextBoxColumn();
col.DataPropertyName = "Select ";
col.HeaderText = "Select";
col.Name = "ColSelect";
dgvDownLoadMaster.Columns.Add(col);
you have to do this for each column and do it before databinding.

Can we filter Datatable with LINQ?

Suppose my datatable is filled with data.
After filling data can we again put some condition on datatable with linq to extract data.
Suppose my datatable has 10 employee record.
So can we extract only those employee whose salary is greater than 5000 with linq query.
I know that we can achieve it datatable.select(). How can you achieve this with linq?
You can get a filtered set of rows, yes:
var query = table.AsEnumerable()
.Where(row => row.Field<decimal>("salary") > 5000m);
This uses the AsEnumerable and Field extension methods in DataTableExtensions and DataRowExtensions respectively.
Try this:
var query = (from t0 in dtDataTable.AsEnumerable()
where t0.Field<string>("FieldName") == Filter
select new
{
FieldName = t0.Field<string>("FieldName"),
FieldName2 = t0.Field<string>("FieldName2"),
});

How to convert a IEnumerable<DataColumn> into a Datatable?

I got this:
var dsetValueFields = rds.Result.Columns.Cast<DataColumn>().Where(c=>c.DataType==typeof(Decimal));
And need to convert into a DataTable. Tried this:
DataTable dt = new DataTable();
dt.Columns.AddRange(dsetValueFields.ToArray());
But get error, "Column is part of another table."
Thanks!
You'll need to create copies of the columns in your enumerable. Like DataRows, DataColumns can only be attached to one table.
dt.Columns.AddRange(dsetValueFields
.Select(c => new DataColumn(c.Name, c.DataType))
.ToArray());

Binding LINQ query to DataGridView

This is very confusing, I use AsDataView to bind query result to a dgv and it works fine with the following:
var query = from c in myDatabaseDataSet.Diamond where c.p_Id == p_Id select c;
dataGridView1.DataSource = query.AsDataView();
However, this one results in an Error:
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
};
dataGridView1.DataSource = query.AsDataView();
Error:
Instance argument: cannot convert from
'System.Collections.Generic.IEnumerable<AnonymousType#1>' to
'System.Data.DataTable'
AsDataView doesn't show up in query.(List). Why is this happen? How to bind the query above to the dgv then?.
The signature of the AsDataView is as follows:
public static DataView AsDataView(
this DataTable table
)
The only parameter is the DataTable.
The query you have is returning an IEnumerable of an anonymous type which doesn't have an implicit conversion to a DataTable (or a sequence of DataRow instances, in which case you could use that to help you create a DataTable).
You need to get the results back into a DataTable or something you can convert into a DataTable and then it will work.
In your particular case, it seems that you were (or are) using typed DataSets. If that is the case, then you should be able to take the values that were selected and then create new typed DataRow instances (there should be factory methods for you) which can then be put into a typed DataTable, which AsDataView can be called on.
just simply convert the result to a list and bind it to your grid.
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
}.ToList();
dataGridView1.DataSource = query;

Resources