Method-Based Query Syntax Examples: Conversion Operators (LINQ to DataSet)
The examples in this topic demonstrate how to use the ToTSource>, ToDictionary, and ToList<TSource> methods to immediately execute a query expression.
The FillDataSet method used in these examples is specified in Loading Data Into a DataSet.
The examples in this topic use the Contact, Address, Product, SalesOrderHeader, and SalesOrderDetail tables in the AdventureWorks sample database.
The examples in this topic use the following using/Imports statements:
Option Explicit On
Imports System
Imports System.Linq
Imports System.Linq.Expressions
Imports System.Collections.Generic
Imports System.Data
Imports System.Data.SqlClient
Imports System.Data.Common
Imports System.Globalization
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Data.Common;
using System.Globalization;
For more information, see How to: Create a LINQ to DataSet Project In Visual Studio.
ToArray
Example
This example uses the ToTSource> method to immediately evaluate a sequence into an array.
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim products As DataTable = ds.Tables("Product")
Dim productsArray = products.AsEnumerable().ToArray()
Dim query = _
From product In productsArray _
Select product _
Order By product.Field(Of Decimal)("ListPrice") Descending
Console.WriteLine("Every price From highest to lowest:")
For Each product In query
Console.WriteLine(product.Field(Of Decimal)("ListPrice"))
Next
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> productsArray = products.AsEnumerable().ToArray();
IEnumerable<DataRow> query =
from product in productsArray
orderby product.Field<Decimal>("ListPrice") descending
select product;
Console.WriteLine("Every price from highest to lowest:");
foreach (DataRow product in query)
{
Console.WriteLine(product.Field<Decimal>("ListPrice"));
}
ToDictionary
Example
This example uses the ToDictionary method to immediately evaluate a sequence and a related key expression into a dictionary.
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim products As DataTable = ds.Tables("Product")
Dim scoreRecordsDict = products.AsEnumerable(). _
ToDictionary(Function(record) record.Field(Of String)("Name"))
Console.WriteLine("Top Tube's ProductID: {0}", _
scoreRecordsDict("Top Tube")("ProductID"))
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
var scoreRecordsDict = products.AsEnumerable().
ToDictionary(record => record.Field<string>("Name"));
Console.WriteLine("Top Tube's ProductID: {0}",
scoreRecordsDict["Top Tube"]["ProductID"]);
ToList
Example
This example uses the ToList<TSource> method to immediately evaluate a sequence into a List<T>, where T is of type DataRow.
' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)
Dim products As DataTable = ds.Tables("Product")
Dim productList = products.AsEnumerable().ToList()
Dim query = _
From product In productList _
Select product _
Order By product.Field(Of String)("Name")
Console.WriteLine("The sorted name list:")
For Each product In query
Console.WriteLine(product.Field(Of String)("Name").ToLower(CultureInfo.InvariantCulture))
Next
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> productList = products.AsEnumerable().ToList();
IEnumerable<DataRow> query =
from product in productList
orderby product.Field<string>("Name")
select product;
Console.WriteLine("The product list, ordered by product name:");
foreach (DataRow product in query)
{
Console.WriteLine(product.Field<string>("Name").ToLower(CultureInfo.InvariantCulture));
}
See Also
Concepts
Standard Query Operators Overview