Voorbeelden van syntaxis van queryexpressie: projectie (LINQ naar dataset)
De voorbeelden in dit onderwerp laten zien hoe u de Select en SelectMany methoden gebruikt om een DataSet query uit te voeren met behulp van de syntaxis van de query-expressie.
De FillDataSet methode die in deze voorbeelden wordt gebruikt, wordt opgegeven in Gegevens laden in een DataSet.
In de voorbeelden in dit onderwerp worden de tabellen Contact, Adres, Product, SalesOrderHeader en SalesOrderDetail gebruikt in de voorbeelddatabase AdventureWorks.
In de voorbeelden in dit onderwerp worden de volgende using/Imports instructies gebruikt:
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Globalization;
using System.Linq;
using System.Windows.Forms;
Option Explicit On
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
Zie How to: Create a LINQ to DataSet Project in Visual Studio (Een LINQ maken naar DataSet-project in Visual Studio) voor meer informatie.
Select
Opmerking
In dit voorbeeld wordt de Select methode gebruikt om alle rijen uit de Product tabel te retourneren en de productnamen weer te geven.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> query =
from product in products.AsEnumerable()
select product;
Console.WriteLine("Product Names:");
foreach (DataRow p in query)
{
Console.WriteLine(p.Field<string>("Name"));
}
' 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 query = From product In products.AsEnumerable() _
Select product
Console.WriteLine("Product Names:")
For Each p In query
Console.WriteLine(p.Field(Of String)("Name"))
Next
Opmerking
In dit voorbeeld wordt een Select reeks alleen productnamen geretourneerd.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable products = ds.Tables["Product"];
IEnumerable<string> query =
from product in products.AsEnumerable()
select product.Field<string>("Name");
Console.WriteLine("Product Names:");
foreach (string productName in query)
{
Console.WriteLine(productName);
}
' 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 query = From product In products.AsEnumerable() _
Select product.Field(Of String)("Name")
Console.WriteLine("Product Names:")
For Each productName In query
Console.WriteLine(productName)
Next
SelectMany
Opmerking
In dit voorbeeld wordt (het equivalent van de SelectMany methode) gebruikt From …, … om alle orders te selecteren waarvoor TotalDue minder dan 500,00 is.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable contacts = ds.Tables["Contact"];
DataTable orders = ds.Tables["SalesOrderHeader"];
var query =
from contact in contacts.AsEnumerable()
from order in orders.AsEnumerable()
where contact.Field<int>("ContactID") == order.Field<int>("ContactID")
&& order.Field<decimal>("TotalDue") < 500.00M
select new
{
ContactID = contact.Field<int>("ContactID"),
LastName = contact.Field<string>("LastName"),
FirstName = contact.Field<string>("FirstName"),
OrderID = order.Field<int>("SalesOrderID"),
Total = order.Field<decimal>("TotalDue")
};
foreach (var smallOrder in query)
{
Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Total Due: ${4} ",
smallOrder.ContactID, smallOrder.LastName, smallOrder.FirstName,
smallOrder.OrderID, smallOrder.Total);
}
' 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 contacts As DataTable = ds.Tables("Contact")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim query = _
From contact In contacts.AsEnumerable() _
From order In orders.AsEnumerable() _
Where (contact.Field(Of Integer)("ContactID") = _
order.Field(Of Integer)("ContactID")) _
And (order.Field(Of Decimal)("TotalDue") < 500D) _
Select New With _
{ _
.ContactID = contact.Field(Of Integer)("ContactID"), _
.LastName = contact.Field(Of String)("LastName"), _
.FirstName = contact.Field(Of String)("FirstName"), _
.OrderID = order.Field(Of Integer)("SalesOrderID"), _
.TotalDue = order.Field(Of Decimal)("TotalDue") _
}
For Each smallOrder In query
Console.Write("ContactID: " & smallOrder.ContactID)
Console.Write(" Name: {0}, {1}", smallOrder.LastName, _
smallOrder.FirstName)
Console.Write(" OrderID: " & smallOrder.OrderID)
Console.WriteLine(" TotalDue: $" & smallOrder.TotalDue)
Next
Opmerking
In dit voorbeeld wordt (het equivalent van de SelectMany methode) gebruikt From …, … om alle orders te selecteren waarin de bestelling is gemaakt op 1 oktober 2002 of hoger.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable contacts = ds.Tables["Contact"];
DataTable orders = ds.Tables["SalesOrderHeader"];
var query =
from contact in contacts.AsEnumerable()
from order in orders.AsEnumerable()
where contact.Field<int>("ContactID") == order.Field<int>("ContactID") &&
order.Field<DateTime>("OrderDate") >= new DateTime(2002, 10, 1)
select new
{
ContactID = contact.Field<int>("ContactID"),
LastName = contact.Field<string>("LastName"),
FirstName = contact.Field<string>("FirstName"),
OrderID = order.Field<int>("SalesOrderID"),
OrderDate = order.Field<DateTime>("OrderDate")
};
foreach (var order in query)
{
Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Order date: {4:d} ",
order.ContactID, order.LastName, order.FirstName,
order.OrderID, order.OrderDate);
}
' 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 contacts As DataTable = ds.Tables("Contact")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim query = _
From contact In contacts.AsEnumerable() _
From order In orders.AsEnumerable() _
Where contact.Field(Of Integer)("ContactID") = order.Field(Of Integer)("ContactID") And _
order.Field(Of DateTime)("OrderDate") >= New DateTime(2002, 10, 1) _
Select New With _
{ _
.ContactID = contact.Field(Of Integer)("ContactID"), _
.LastName = contact.Field(Of String)("LastName"), _
.FirstName = contact.Field(Of String)("FirstName"), _
.OrderID = order.Field(Of Integer)("SalesOrderID"), _
.OrderDate = order.Field(Of DateTime)("OrderDate") _
}
For Each order In query
Console.Write("Contact ID: " & order.ContactID)
Console.Write(" Name: " & order.LastName & ", " & order.FirstName)
Console.Write(" Order ID: " & order.OrderID)
Console.WriteLine(" Order date: {0:d} ", order.OrderDate)
Next
Opmerking
In dit voorbeeld wordt een From …, … (het equivalent van de SelectMany methode) gebruikt om alle orders te selecteren waarbij het ordertotaal groter is dan 10000,00 en toewijzing gebruikt From om te voorkomen dat het totaal twee keer wordt aangevraagd.
// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);
DataTable contacts = ds.Tables["Contact"];
DataTable orders = ds.Tables["SalesOrderHeader"];
var query =
from contact in contacts.AsEnumerable()
from order in orders.AsEnumerable()
let total = order.Field<decimal>("TotalDue")
where contact.Field<int>("ContactID") == order.Field<int>("ContactID") &&
total >= 10000.0M
select new
{
ContactID = contact.Field<int>("ContactID"),
LastName = contact.Field<string>("LastName"),
OrderID = order.Field<int>("SalesOrderID"),
total
};
foreach (var order in query)
{
Console.WriteLine("Contact ID: {0} Last name: {1} Order ID: {2} Total: {3}",
order.ContactID, order.LastName, order.OrderID, order.total);
}
' 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 contacts As DataTable = ds.Tables("Contact")
Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim query = _
From contact In contacts.AsEnumerable() _
From order In orders.AsEnumerable() _
Let total = order.Field(Of Decimal)("TotalDue") _
Where contact.Field(Of Integer)("ContactID") = order.Field(Of Integer)("ContactID") And _
total >= 10000D _
Select New With _
{ _
.ContactID = contact.Field(Of Integer)("ContactID"), _
.LastName = contact.Field(Of String)("LastName"), _
.OrderID = order.Field(Of Integer)("SalesOrderID"), _
.OrderDate = order.Field(Of DateTime)("OrderDate"), _
total _
}
For Each order In query
Console.Write("Contact ID: " & order.ContactID)
Console.Write(" Last Name: " & order.LastName)
Console.Write(" Order ID: " & order.OrderID)
Console.WriteLine(" Total: $" & order.total)
Next