Andrew的部落格

利用 LInQ 查詢 DataTable

使用 Select

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;

1.

IEnumerable<DataRow> query =
    from product in products.AsEnumerable()
    select product;

foreach (DataRow p in query)
{
    Console.WriteLine(p.Field<string>("Name"));
}

2.

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);
}

Select Manay

利用 LInQ 的Select Many 查詢兩個 Datatable 的 join 功能

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);
}

使用LNIQ ,選取日期為2002 年 10 月 1 日或之後下單的所有訂單。

1.

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")
    };

2.增加一個變數來做條件約束

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
                };