Currently I'm searching as below.
DataRow[] rows =
dataTable.Select("FieldName='"+
userInput + "'");
The problem here is whenever user provides an input with single quote ('), it throws error.
I can easily correct it by
DataRow[] rows =
dataTable.Select("FieldName='" +
userInput.Replace("'","''") + "'");
I'm worried what other user inputs might cause problem?
Here is the exact answer from honourable Mr. Jon Skeet.
#Ismail: It would be a good habit if we validate user input before using that in front end query or in back-end query.
So i think in your scenario you must have function like...
if(ValidateInput(userInput))
{
DataRow[] rows = dataTable.Select("FieldName='"+ userInput + "'");
}
and in validation you can do any check. right now you only want to check ' but in future, may be you will have to check some thing else.
and based on your need you can checge return type of validate function, if you want to modify input data then modify and return that else just return bool.
If you want to use DataTable.Select(filter) for data filter then you have to format/ignore or replace special character from filter statement and for that u will have to write more code. If you dont want to be panic for special character then you can use LINQ like
DataTable dataTable = new DataTable();
DataColumn dc = new DataColumn("FieldName");
dataTable.Columns.Add(dc);
DataRow dr = dataTable.NewRow();
dr[0] = "D'sulja";
dataTable.Rows.Add(dr);
string input = "D'sulja";
var result = from item in dataTable.AsEnumerable()
where item.Field<string>("FieldName") == input select item;
In this case, I think the single quote is the only character you have to worry about since it is used to delimit string values. For more information on expression syntax, see the MSDN entry for DataColumn.Expression (creating a filter expression uses the same rules as for the DataColumn.Expression property).
You don't indicate which version of C# you are using, but with LINQ, you can do this:
var rows = table.AsEnumerable()
.Where(r => r.Field<string>("Name") == "O'Hare")
.Select(r => r)
.ToArray();
One tradeoff is that you'll also need to check the RowState if you have any deleted rows in the DataTable, but it does provide another option.
Related
I have a datatable that has a column "Pending Approval Number". I need to get the highest number in that column to display to a user as the next available. I have seen some examples of how to do this but I have not been able to get them to work. I know i could loop each DataRow in the DataTable and check the value and store it if it is higher than the last. But I know there has to be a better way.
Here is how the DataTable is filled.
strSQL = "Select * from JobInvoice";
DataTable dtApprovalNumber = new DataTable();
MySqlDataAdapter daApprovalNumber = new MySqlDataAdapter(strSQL, conn);
daApprovalNumber.Fill(dtApprovalNumber);
A change to the SQL query or code to pull it from the datatable are both welcome.
EDIT: After getting the solution for my original numeric column, I found the second column that I need to do this for is string. The solution was also provided below.
If You want to get highest Value from DataTable in code not in sql, then You can just use linq like below:
int highestNumber = dtApprovalNumber.AsEnumerable().Max(x => x.Field<int>("SomeIntegerColumn");
EDIT.
According to Your comment - if You want to calculate max value from a string column which holds numbers(don't get it why) You can go with something like that:
int highestNumber = dtApprovalNumber.AsEnumerable().Max(x => int.Parse(x.Field<string>("SomeStringColumn")));
Please Note that if any of those string values is not convertable it will fail then You will have to do it other way.
EDIT.2
Since I've just tried it I'll share with You - the situation when You have string Column and You are not sure if all of them are convertable(for example some might be empty). See below:
int tempVariable;
int highestNumber = dt.AsEnumerable()
.Where(x => int.TryParse(x.Field<string>("SomeColumn"), out tempVariable))
.Max(m => int.Parse(m.Field<string>("SomeColumn")));
Select max(`Pending Approval Number`) from JobInvoice
You can do a maxvalue + 1 to show it as next available number.
This is a fairly simple question, though I am unsure of exactly how to go about it. I'm doing a query on a database, then inserting the pulled value into a textbox. However the query could return a null value, here is my problem. If the query returns a null then the textbox should display 19. I'm unsure of how to check the returned data to determine if null was returned so that 19 can be inserted into the textbox. here is my code (it works putting the returned value into the textbox its missing the check for null/add 19)
using (test1 ds = new test1())
{
DataTable dt = ds.dataset.Tables[0];
List<string> coolList = new List<string>();
foreach (DataRow row in dt.Rows)
{
coolList.Add(row[0].ToString());
}
textBox7.Text = string.Join(" ", coolList);
}
Better not use null. Simple write in your SQL: SELECT IsNull(YourColumn, 19) as YourColumn FROM WhatEver. Than you have solved your problem directly in sql.
string rowString = !String.IsNullOrEmpty(row[0].ToString()) ? row[0].ToString() : "19";
coolList.Add(rowString);
You can use String.IsNullOrWhiteSpace instead if you're using .NET 4 or newer.
Instead of creating a List<string> , you can use LINQ to DataSet/DataTable like:
textBox7.Text = string.Join(" ",
dt.AsEnumerable()
.Select(r => string.IsNullOrWhiteSpace(r.Field<string>(0))
? "19"
: r.Field<string>(0)));
Using ISNULL is whatcha need to handle this.
I currently have a DataTable with the following columns: Date, X1, Y1, Z1, X2, Y2, Z2... Xn, Yn, Zn.
When populated, Date ALWAYS has a value, and X/Y/Z1 to X/Y/Zn can be DBNull, a string, or an int. If the entire row with the exception of Date, is DBNull, i would like to remove that particular row.
I am currently doing an exhaustive search, looping through each row with a for loop, and then with a nested for loop, checking each cell, if i do not find any data (ie. only dbnull's), i then call RemoveAt, and reset the outer loop to start at zero again.
Is there a better/less hacky way of performing this operation? The initial building of the datatable cannot be modified, this must be something that happens post building.
If I understand correctly, you want to remove a row if all columns has DbNull.Value.
Try the following to do that.
DataTable table = new DataTable();
string[] columns = table.Columns.Cast<DataColumn>()
.Select(x => x.ColumnName)
.Skip(1)//skip to ignore first column
.ToArray();
Method1:
Remove all invalid rows
var invalidRows = table.AsEnumerable()
.Where(x => columns.All(c => x.Field<object>(c) == DBNull.Value))
.ToArray();
foreach (var row in invalidRows)
{
table.Rows.Remove(row);
}
Method2: take only valid rows and make new DataTable as suggested my #Tim in comments to improve performance when you have many invalid rows
var newTable = table.AsEnumerable()
.Where(x => columns.Any(c => x.Field<object>(c) != DBNull.Value))
.CopyToDataTable();
ATTENTION : THESE ARE MY EXAMPLES>>NOT EXCATLLY FOR YOUR TABLE>>>SO CHANGE IT FOR YOURSELF
The Main Help is Here >> Help
And Then
Way one :
dtData.Select("ID=1 AND ID2=3");
Way two :
GridFieldDAO dao = new GridFieldDAO();
//Load My DataTable
DataTable dt = dao.getDT();
//Get My rows based off selection criteria
DataRow[] drs = dt.Select("(detailID = 1) AND (detailTypeID = 2)");
//make a new "results" datatable via clone to keep structure
DataTable dt2 = dt.Clone();
//Import the Rows
foreach (DataRow d in drs)
{
dt2.ImportRow(d);
}
//Bind to my new DataTable and it will only show rows based off selection
//criteria
myGrid.DataSource = dt2;
myGrid.DataBind();
And The best Way is :
DataTable tblFiltered = table.AsEnumerable()
.Where(row => row.Field<String>("Nachname") == username
&& row.Field<String>("Ort") == location)
.OrderByDescending(row => row.Field<String>("Nachname"))
.CopyToDataTable();
May be this will help you. Try this
var ordered = yourdatatable.AsEnumerable().Where(x => x.Field<DateTime>("ColumnName") != null);
if (ordered.Count() > 0)
{
yourdatatable= orderedCopyToDataTable();
}
you can do the same for other columns as well.
Or
Why don't you check for the null values in your query. check for ISNULL(columnName, value) As ColumnName. Check more details here
You can use this little Linq query:
var columnsWithoutDate = table.Columns.Cast<DataColumn>().Skip(1);
table = table.AsEnumerable()
.Where(row => columnsWithoutDate.Any(col => !row.IsNull(col)))
.CopyToDataTable();
Skip(1) returns all columns but the first, so your date column is excluded. The Where enumerates all DataRows in the table and takes all rows with at least one non-null field(see:DataRow.IsNull(column)). Finally CopyToDataTable creates a new DataTable.
I would go for something like this:
var test = from row in table.AsEnumerable()
where (!row.IsNull("col1") || !row.IsNull("col2"))
select row;
//option1
DataTable dt = test.CopyToDataTable<DataRow>();
//option2
DataTable dt2 = new DataTable();
dt2.Columns.Add("col1", typeof(String));
dt2.Columns.Add("col2", typeof(Int32));
foreach (var v in test)
{
DataRow dr = dt2.NewRow();
dr["col1"] = v.Field<String>("col1");
dr["col1"] = v.Field<Int32>("col2");
dt2.Rows.Add(dr);
}
Did you try using RowFilter of DataTable?
DataTable dt = GetData();
//set the filter
dt.DefaultView.RowFilter = "----your filter----";
//then access the DataView
foreach (DataRowView drv in dt.DefaultView)
{
//you can also get a row from rowview
DataRow dr = drv.Row;
}
Check this documentation, they also explain how to handle null values in filters.
http://msdn.microsoft.com/en-us/library/system.data.dataview.rowfilter.aspx
You can also use Select() method with same filter, refer the below answer there is a good comparison on both approach.
DataView.RowFilter Vs DataTable.Select() vs DataTable.Rows.Find()
I would not suggest using AsEnumerable() approach, though looks like simple code but it is just like doing a foreach loop on rows and having IF conditions.
DataTable filter approach should be faster than AsEnumerable() (I am not sure, but I am assuming this because DataTable is .net's powerful data structure to handle tabular data)
modified answer:
myDataTable.AsEnumerable().Where(a => a.ItemArray.Count(b=>b != DBNull.Value)==1).ToList().ForEach(row => dataTable.Rows.Remove(row));
I checked, it works.
EDIT:
in response to #Tim Schmelter comment:
1 . you need myDataTable.AsEnumerable() in C#
If you have a strongly typed DataTable, you do not. I assumed it's the case, since OP says:
The initial building of the datatable cannot be modified, this must be
something that happens post building.
Maybe I did't understand what he meant (my English sometimes fails me)
2 . count the non-null fields is incorrect since a string can be null
which is not the same as if it is DBNull.Value(also according OP's
specifications)
You are probably right. If OP says he only wants DBNull, the second condition should be removed (it's a bad habit of mine to check for null just in case)
3 . ToList creates another List which is redundant
Yes. And if there's no ToList(), ForEach() can't be used. The old fashioned foreach can be used instead, or beter for loop (since foreach doesn't like when you try to modify collection inside it). Still you have to keep your result in some way.
4 . DataRow.Delete does it not remove from the table what is desired,
but it flags it as deleted for a DataAdapter(OP's has not mentioned
that he's using one, it is also not desired).
Thank you for pointing that out.
I'm new to writing LINQ queries, and I'm having trouble with string comparisons. I'm loading the data into a DataTable (confirmed that table in SQL DB and DataTable have same number of rows), but for some reason I can't find a value that I know exists in both.
The text box contains 'servername' while the datarows contain 'servername.mydomain.net', so here's what my code looks like
string strParameter = txtAutoComplete.ToString().ToLower();
//WUG TableAdapter and DataTable
dsCIInfoTableAdapters.DeviceTableAdapter taWUG;
taWUG = new dsCIInfoTableAdapters.DeviceTableAdapter();
dsCIInfo.DeviceDataTable dtWUG = new dsCIInfo.DeviceDataTable();
taWUG.Fill(dtWUG);
var qstWUG = (from row in dtWUG.AsEnumerable()
where row.Field<string>("sDisplayName").ToLower().Contains(strParameter)
select row.Field<string>("sDisplayName"));
Beleive in your LINQ statement dtWUG needs to be dtWUG.AsEnumerable(). Linq only works on data sources that implement the IEnumerable Interface.
You can debug it easier if you add some let statements where you can add breakpoints:
var qstWUG = (from row in dtWUG
let display = row.Field<string>("sDisplayName")
let lower = display.ToLower()
let contains = lower.Contains(strParameter)
where contains
select display).ToArray();
Also convert it to an array using .ToArray() at the end, will make it execute immediately (LINQ is lazy by paradigm, doesn't execute until it's needed), and also easier to look at in subsequent breakpoints.
Yeah, I feel stupid... I forgot to use the textbox.text to assign it to a string
string strParameter = txtAutoComplete.Text.ToLower();
//WUG TableAdapter and DataTable
dsCIInfoTableAdapters.DeviceTableAdapter taWUG;
taWUG = new dsCIInfoTableAdapters.DeviceTableAdapter();
dsCIInfo.DeviceDataTable dtWUG = new dsCIInfo.DeviceDataTable();
taWUG.Fill(dtWUG);
var qstWUG = (from row in dtWUG.AsEnumerable()
let display = row.Field<string>("sDisplayName")
where display.ToLower().Contains(strParameter)
select display).ToArray();
I am retrieving data from an MSSQL server using the SqlDataAdapter and DataSet. From that DataSet I am creating a DataTable. My goal is to convert each column of the table into a string where the elements are comma delimited. I figured that I would try the string conversion first before making the delimiter work.
The code runs in the code-behind of an ASP.Net page. The ultimate goal is to pass the string to a jscript variable, it's a "functional requirement" that I create a delimited string from the columns and that it has to end up as a jscript variable.
Here's what I have thus far:
DataSet myDataSet = new DataSet();
mySqlDataAdapter.Fill(myDataSet);
DataTable temperature = myDataSet.Tables["Table"];
// LOOP1
foreach (DataRow row in temperature.Rows)
// this loop works fine and outputs all elements
// of the table to the web page, this is just to
// test things out
{
foreach (DataColumn col in temperature.Columns)
{
Response.Write(row[col] + " ### ");
}
Response.Write("<br>");
}
// LOOP2
foreach (DataColumn column in temperature.Columns)
// this loop was meant to take all elements for each
// column and create a string, then output that string
{
Response.Write(column.ToString() + "<br>");
}
In LOOP1 things work fine. My data has 4 columns, all are appropriately rendered with one record per row on the web page.
I saw the code for LOOP2 at http://msdn.microsoft.com/en-us/library/system.data.datacolumn.tostring.aspx which seems to do exactly what I need except it does not actually do what I want.
The only thing LOOP2 does is write 4 lines to the web page. Each line has the header of the respective table column but none of the additional data. Clearly there's either a logic flaw on my part or I misunderstand how DataColumn and .toString for it works. Please help me out on this one. Thanks in advance.
EDIT:
Here's an SQL query result example, this is what the Table looks like:
Table quesry result # ImageShack
What I want to end up are four strings, here's an example for the string that would be created from the second column: "-6.7, -7, -7.2, -7.3, -7.3".
This code will concatenate values from cells under each column with ", ":
foreach (var column in temperature.Columns)
{
DataColumn dc = column as DataColumn;
string s = string.Join(", ", temperature.Rows.OfType<DataRow>()
.Select(r => r[dc]));
// do whatever you need with s now
}
For example, for DataTable defined as:
DataTable table = new DataTable();
table.Columns.Add(new DataColumn("Column #1"));
table.Columns.Add(new DataColumn("Column #2"));
table.Rows.Add(1, 2);
table.Rows.Add(11, 22);
table.Rows.Add(111, 222);
... it will produce "1, 11, 111" and "2, 22, 222" strings.
Edit: I saw you chose to declare column as var as opposed to DataColumn, is that a matter of personal preference/style or is there an issue with coding?
Consider following scenario (on the same data table example as above):
// we decide we'll use results later, storing them temporarily here
List<IEnumerable<string>> columnsValues = new List<IEnumerable<string>>();
foreach (DataColumn column in temperature.Columns)
{
var values = temperature.Rows.OfType<DataRow>()
.Select(r => r[column].ToString())
columnsValues.Add(values);
}
We assume we now got list of list of column values. So, when we print them, like this:
foreach (var lisOfValues in columnsValues)
{
foreach (var value in listOfValues)
{
Debug.Write(value + " ");
}
Debug.WriteLine("");
}
We expect to see 1 11 111 followed by 2 22 222. Right?
Wrong.
This code will output 2 22 222 twice. Why? Our .Select(r => r[column].ToString()) captures column variable - not its value, but variable itself - and since we don't use it immediately, once we're out of loop all we know is last value of column.
To learn more about this concept search for closures and captured variables - for example, in posts like this.
Summary:
In this very case you can go with DataColumn in foreach statement. It doesn't matter here because we're enumerating through our .Select(r => r[dc]) either way inside the loop (precisely, string.Join does that for us), producing results before we get to next iteration - whatever we capture, is used immediately.
The link you have posted clearly states
The Expression value, if the property
is set; otherwise, the ColumnName
property.
and that is what is happening. You get column names.
This could help: How to convert a DataTable to a string in C#?