I need advice on how to go about a problem I have with sorting a DataView in C#.
I need to add a sort property to my DataView because I later need it when I call a Find on the DataView (which needs to have a sort property specified in order to work). I need the Find in order to properly map a DataRow to a DataGridViewRow. I currently just use the row index to map to the DataGridViewRow, but this won't work in all cases if the user physically moves rows, or changes the sort order in the DataGridView (UI) because then the ids no longer match-up/map.
When I create the DataView, I load in a DataTable to pass in for creation. This DataTable can be of any form, I do not know what the DataTable contains for columns and rows. Therefore, I cannot create a sort if I don't know any column names to sort by.
I was thinking of just taking the first column name (column[0]) - no matter what it is and using that to sort. But this seems kinda sketchy, no?
My question is, is there a better way to determine what to sort my DataView by when column names are unknown?
Thanks!
I haven't tried it, but since it sorts based on the column name you pass in, couldn't you sort based on index with something like:
dataview.Sort = dataview.Table.Columns[index].ColumnName + " DESC";
Related
I have a datatable with almost 20 columns in it. in another DT i get only the columns I want. Recently my requirements have changed i.e. Firstly the number of columns in the original DT were constant but now it increases or decreases depending upon the data.
So now, if I statically provide the column names I need in my new DT it isnt of much use to me.
Is there any way in which I can include those columns which may or may not be in the Original Datatable????
For eg: col1|col2|col3|.......col20.
The columns that may bve present or absent fall between col12 and col 16. Is there anyway in which I could make it work????
EDIT:
I want col1,col2,col3 and all columns aftr col12...can I do it???
You can have total number of columns from datatable using
DataTable.Columns.Count
So you will know how many columns are there and you will know which column is in datatable and which is not.
I want to get the most frequent value for every column in my DataTable.
I found an answer to a similar question for a Table, but it does not seem to work for my DataTable.
Actually I would welcome a list of distinct values for every column.
I'm using a DataTable as the datasource for my ComboBox and I need to sort the Data into a strict order. The problem is that the I don't need in Ascending Order or Descending, it's how the customer see's the items as a priority, so there's not really any logic too it.
Will I need to create a column that has an ordering value and then sort the data by that column? I'm just looking for the best way to do this. In time, more items may be added and the ordering may need to change. This is something i want to achieve without hard coding each time.
The Data at present only has two columns, which look like below:-
ApplicationName | ApplicationType
I just need the best way of doing this.
Thanks
I'm using a SqlDataReader to add row by row into a datatable like follows:
while (reader.Read())
{
dataTable.LoadDataRow(reader.CurrentRow(), LoadOption.PreserveChanges);
}
This works, but I need to be able to avoid adding duplicate rows to the dataTable. I would love to be able to use the Contains or Find methods from the dataTable, but I can't find a way to turn the object[] from reader.CurrentRow() into a DataRow to compare to without adding it to a datatable.
I've looked into the option of making a hashset of the object[]s, and then adding them all at once to the datatable at the end, but I forgot that the default object IEqualityComparer only compares the reference.
Is there a feasible way of doing this without removing the duplicates at the end?
If removing the duplicates is the only way to go, what is the best way to do that?
EDIT:
I'm splitting distinct rows from the database into separate datatables in code. Each row from the query result is distinct, but sections of each row are not. Unfortunately I need to do exactly what my question is asking, as the results from the query are already distinct.
You didn't provide a ton of detail, but I hope this is comprehensive.
If you need a single column to be unique, then in your Columns collection in your datatable, specify the column like this:
DataTable appeals = new DataTable("Appeals");
appeals.Columns["PriorAppealNumber"].Unique = true;
DataColumn keyField = new DataColumn("AppealNumber", typeof(string));
appeals.Columns.Add(keyField);
If the uniqueness needs to span multiple rows, this is the method:
var myUniqueConstraint = new UniqueConstraint( new DataColumn[] {appeals.Columns[0], appeals.Columns[1], appeals.Columns[2]} );
appeals.Constraints.Add(myUniqueConstraint);
That will enforce the constraints BEFORE you try to commit back to the source database.
The easiest way is to actually make sure there are no duplicate rows at all - if you're querying relational database use DISTINCT - that will return only unique rows.
DataRow contains a Table property, which seems to return the entire Table for which this row belongs.
I'd like to know if I can use that table safely, or if there are gotcha's.
In http://msdn.microsoft.com/en-us/library/system.data.datarow.table.aspx documentation, it says "A DataRow does not necessarily belong to any table's collection of rows. This behavior occurs when the DataRow has been created but not added to the DataRowCollection.", but I know for a fact my row belongs to a table.
In terms of pointers, if each Row from DataTable points to original DataTable, than I'm good to go. Is that all 'Table' property does?
Just to explain why I'm trying to get entire Table based on a single DataRow:
I'm using linq to join two (sometimes more) tables. I'd like to have a generic routine which takes the output of linq (var), and generate a single DataTable with all results.
I had opened another question at stackoverflow (Join in LINQ that avoids explicitly naming properties in "new {}"?), but so far there doesn't seem to be a generic solution, so I'm trying to write one.
if you know the row is part of table than yes you can access it without any problem. if the possibility exists where the row may not be associated to a table than check if the property is null.
if(row.Table == null)
{
}
else
{
}
As long as it's not null, you can use it freely.