I'm trying to perform a LINQ query on a DataTable object and bizarrely I am finding that performing such queries on DataTables is not straightforward. For example:
var results = from myRow in myDataTable
where results.Field("RowNo") == 1
select results;
This is not allowed. How do I get something like this working?
I'm amazed that LINQ queries are not allowed on DataTables!
For VB.NET The code will look like this:
Dim results = From myRow In myDataTable
Where myRow.Field(Of Int32)("RowNo") = 1 Select myRow
This is a simple way that works for me and uses lambda expressions:
var results = myDataTable.Select("").FirstOrDefault(x => (int)x["RowNo"] == 1)
Then if you want a particular value:
if(results != null)
var foo = results["ColName"].ToString()
IEnumerable<string> result = from myRow in dataTableResult.AsEnumerable()
select myRow["server"].ToString() ;
It's not that they were deliberately not allowed on DataTables, it's just that DataTables pre-date the IQueryable and generic IEnumerable constructs on which Linq queries can be performed.
Both interfaces require some sort type-safety validation. DataTables are not strongly typed. This is the same reason why people can't query against an ArrayList, for example.
For Linq to work you need to map your results against type-safe objects and query against that instead.
You can use LINQ to objects on the Rows collection, like so:
var results = from myRow in myDataTable.Rows where myRow.Field("RowNo") == 1 select myRow;
In my application I found that using LINQ to Datasets with the AsEnumerable() extension for DataTable as suggested in the answer was extremely slow. If you're interested in optimizing for speed, use James Newtonking's Json.Net library (http://james.newtonking.com/json/help/index.html)
// Serialize the DataTable to a json string
string serializedTable = JsonConvert.SerializeObject(myDataTable);
Jarray dataRows = Jarray.Parse(serializedTable);
// Run the LINQ query
List<JToken> results = (from row in dataRows
where (int) row["ans_key"] == 42
select row).ToList();
// If you need the results to be in a DataTable
string jsonResults = JsonConvert.SerializeObject(results);
DataTable resultsTable = JsonConvert.DeserializeObject<DataTable>(jsonResults);
I realize this has been answered a few times over, but just to offer another approach:
I like to use the .Cast<T>() method, it helps me maintain sanity in seeing the explicit type defined and deep down I think .AsEnumerable() calls it anyways:
var results = from myRow in myDataTable.Rows.Cast<DataRow>()
where myRow.Field<int>("RowNo") == 1 select myRow;
or
var results = myDataTable.Rows.Cast<DataRow>()
.FirstOrDefault(x => x.Field<int>("RowNo") == 1);
As noted in comments, no other assemblies needed as it's part of Linq (Reference)
//Json Formating code
//DT is DataTable
var filter = (from r1 in DT.AsEnumerable()
//Grouping by multiple columns
group r1 by new
{
EMPID = r1.Field<string>("EMPID"),
EMPNAME = r1.Field<string>("EMPNAME"),
} into g
//Selecting as new type
select new
{
EMPID = g.Key.EMPID,
MiddleName = g.Key.EMPNAME});
var results = from DataRow myRow in myDataTable.Rows
where (int)myRow["RowNo"] == 1
select myRow
You can get it work elegant via linq like this:
from prod in TenMostExpensiveProducts().Tables[0].AsEnumerable()
where prod.Field<decimal>("UnitPrice") > 62.500M
select prod
Or like dynamic linq this (AsDynamic is called directly on DataSet):
TenMostExpensiveProducts().AsDynamic().Where (x => x.UnitPrice > 62.500M)
I prefer the last approach while is is the most flexible.
P.S.: Don't forget to connect System.Data.DataSetExtensions.dll reference
//Create DataTable
DataTable dt= new DataTable();
dt.Columns.AddRange(new DataColumn[]
{
new DataColumn("ID",typeof(System.Int32)),
new DataColumn("Name",typeof(System.String))
});
//Fill with data
dt.Rows.Add(new Object[]{1,"Test1"});
dt.Rows.Add(new Object[]{2,"Test2"});
//Now Query DataTable with linq
//To work with linq it should required our source implement IEnumerable interface.
//But DataTable not Implement IEnumerable interface
//So we call DataTable Extension method i.e AsEnumerable() this will return EnumerableRowCollection<DataRow>
// Now Query DataTable to find Row whoes ID=1
DataRow drow = dt.AsEnumerable().Where(p=>p.Field<Int32>(0)==1).FirstOrDefault();
//
var query = from p in dt.AsEnumerable()
where p.Field<string>("code") == this.txtCat.Text
select new
{
name = p.Field<string>("name"),
age= p.Field<int>("age")
};
the name and age fields are now part of the query object and can be accessed like so: Console.WriteLine(query.name);
Using LINQ to manipulate data in DataSet/DataTable
var results = from myRow in tblCurrentStock.AsEnumerable()
where myRow.Field<string>("item_name").ToUpper().StartsWith(tbSearchItem.Text.ToUpper())
select myRow;
DataView view = results.AsDataView();
Try this
var row = (from result in dt.AsEnumerable().OrderBy( result => Guid.NewGuid()) select result).Take(3) ;
Try this simple line of query:
var result=myDataTable.AsEnumerable().Where(myRow => myRow.Field<int>("RowNo") == 1);
Example on how to achieve this provided below:
DataSet dataSet = new DataSet(); //Create a dataset
dataSet = _DataEntryDataLayer.ReadResults(); //Call to the dataLayer to return the data
//LINQ query on a DataTable
var dataList = dataSet.Tables["DataTable"]
.AsEnumerable()
.Select(i => new
{
ID = i["ID"],
Name = i["Name"]
}).ToList();
As @ch00k said:
using System.Data; //needed for the extension methods to work
...
var results =
from myRow in myDataTable.Rows
where myRow.Field<int>("RowNo") == 1
select myRow; //select the thing you want, not the collection
You also need to add a project reference to System.Data.DataSetExtensions
I propose following solution:
DataView view = new DataView(myDataTable);
view.RowFilter = "RowNo = 1";
DataTable results = view.ToTable(true);
Looking at the DataView Documentation, the first thing we can see is this:
Represents a databindable, customized view of a DataTable for sorting, filtering, searching, editing, and navigation.
What I am getting from this is that DataTable is meant to only store data and DataView is there enable us to "query" against the DataTable.
Here is how this works in this particular case:
You try to implement the SQL Statement
SELECT *
FROM myDataTable
WHERE RowNo = 1
in "DataTable language". In C# we would read it like this:
FROM myDataTable
WHERE RowNo = 1
SELECT *
which looks in C# like this:
DataView view = new DataView(myDataTable); //FROM myDataTable
view.RowFilter = "RowNo = 1"; //WHERE RowNo = 1
DataTable results = view.ToTable(true); //SELECT *
you can try this, but you must be sure the type of values for each Column
List<MyClass> result = myDataTable.AsEnumerable().Select(x=> new MyClass(){
Property1 = (string)x.Field<string>("ColumnName1"),
Property2 = (int)x.Field<int>("ColumnName2"),
Property3 = (bool)x.Field<bool>("ColumnName3"),
});
var results = from myRow in myDataTable
where results.Field<Int32>("RowNo") == 1
select results;
Most likely, the classes for the DataSet, DataTable and DataRow are already defined in the solution. If that's the case you won't need the DataSetExtensions reference.
Ex. DataSet class name-> CustomSet, DataRow class name-> CustomTableRow (with defined columns: RowNo, ...)
var result = from myRow in myDataTable.Rows.OfType<CustomSet.CustomTableRow>()
where myRow.RowNo == 1
select myRow;
Or (as I prefer)
var result = myDataTable.Rows.OfType<CustomSet.CustomTableRow>().Where(myRow => myRow.RowNo);
Try this...
SqlCommand cmd = new SqlCommand( "Select * from Employee",con);
SqlDataReader dr = cmd.ExecuteReader( );
DataTable dt = new DataTable( "Employee" );
dt.Load( dr );
var Data = dt.AsEnumerable( );
var names = from emp in Data select emp.Field<String>( dt.Columns[1] );
foreach( var name in names )
{
Console.WriteLine( name );
}
Source: Stackoverflow.com