Linq la evolución de ADO .net

Una de las grandes novedades de Visual Studio 2008 y de .NET Framework 3.5 es el Language Integrated Query (LINQ) que habilita la definición de consultas integradas en el lenguaje de programación y es una de las piedras angulares de las nuevas versiones de C# y VB. Precisamente. No es facil dejar atras nuestros Dataset y nuestros amigos DataAdapters pero es momento de continuar, un consejo para superar la perdida es que imaginen que adonet(dataset,dataadapter,connection) era su carro viejo que funciona y esta perferto sin embargo salio el nuevo de agencia y que esta mejor, corre mas rapido, es mas eficiente, mas bonito y no daña el ambiente.

asi que para ayudarlos a migrarse les doy unos ejemplos con connecion a bases de datos sql server.

Lo primero es la hacer la connecion para lograr esto agreguen un nuevo item en su proyecto y elijan linq.
ejemplo:



ahora ya agregado el dbml tiene que agregar las tablas del server explorer:


bueno ahora ha jugar:
hagamos queries:


Primero la consulta comun:
DataClassesDataContext db = new DataClassesDataContext();
var clientes = from c in db.Customers
select new {c.CustomerID, c.CompanyName, c.ContactName, c.Country,c.City };

como usar el resultado
usando Bind
GridView1.DataSource = clientes;
GridView1.DataBind();


o leerlo con un ciclo:
foreach (var customer in clientes )
{
Console.WriteLine("Customer {0}: {1}", customer.CustomerId, customer.CompanyName);
}


Like

para usar like tiene que hacer un using System.Data.Linq.SqlClient;

DataClassesDataContext db = new DataClassesDataContext();
var clientes = from c in db.Customers
where SqlMethods.Like(c.Country, "%" + TextBox1.Text + "%")
select new {c.CustomerID, c.CompanyName, c.ContactName, c.Country,c.City };


Concatenar dos campos
var query = from c in db.Customers
where c.customerid==txtcodito.text && c.country=="spain"
select new { c.Nombre, nombrecompleto = string.Format("{0} {1}", c.companyname,c.contactname) };

execute scalar ejemplo con function
string nombre=(from c in db.customers where p.customerid== txtusuario.text select c.companyname).Single();

string nombre=(from c in db.customers
 where p.customerid== txtusuario.text select c).Single().companyname;

Group by

var pais = from p in db.Customers
group p by new { p.Country } into r
select new { r.Key.Country };


var rows = from item in TablaEmpleado.AsEnumerable()
           group item by
                   new
                       {
                          empid = item["employeeid"].ToString(),
                          depto = item["DeptoId"].ToString()
                        }
           into g
              select new
                       {
                         EmpresaId = g.Key. empid,
                         depto = g.Key. depto,
                         total = g.Count())
                       };


 Sum en linq


System.Nullable totalFreight =
    (from ord in db.Orders
    select ord.Freight)
    .Sum();


System.Nullable totalUnitsOnOrder =
    (from prod in db.Products
    select (long)prod.UnitsOnOrder)
    .Sum();

in en linq
string[] countries = new string[] { "Guatemala", "USA", "Mexico" };
var customers =from c in context.Customers
where countries.Contains(c.Country)
select c;

comentario:
Eve para que mire que la tomo en cuenta.


Between
var query = from p in db.orders
where p.Fecha >= Convert.ToDateTime(TextBox1.Text) && p.Fecha <= Convert.ToDateTime(TextBox2.Text) select new { p.Fecha };

Distinct

var query = (from c in db.customers
       orderby c.country
select c.country).Distinct();




Join
var groupJoinQuery2 =
from category in categories
join prod in products on category.ID equals prod.CategoryID
orderby category.Name
select new
{
Category = category.Name,
Products = prod.Name
};




sub consulta

var groupJoinQuery2 =
from category in categories
join prod in products on category.ID equals prod.CategoryID into prodGroup
orderby category.Name
select new
{
Category = category.Name,
Products = from prod2 in prodGroup
orderby prod2.Name
select prod2
};


Left Outer Joins

var query = (from p in dc.GetTable()
join pa in dc.GetTable() on p.Id equals pa.PersonId into tempAddresses
from addresses in tempAddresses.DefaultIfEmpty()
select new { p.FirstName, p.LastName, addresses.State });

SQL:

SELECT [t0].[FirstName], [t0].[LastName], [t1].[State] AS [State]
FROM [dbo].[Person] AS [t0]
LEFT OUTER JOIN [dbo].[PersonAddress] AS [t1] ON [t0].[Id] = [t1].[PersonID]



mas ejemplos de join clic aquí

si son de las personas que usan Store Procedure
pues bien es mas facil =)

lo primero que tiene que hacer es bajar el sp de server explorar al contex del linq


codigo:
//Obtaining the data source
var dbNorthwind =new NorthwindDataContext() ;

// Create the query
var query = dbNorthwind.SalesByCategory("Beverages","1997");

// Execute the query
foreach (var c in query)
{
Console.WriteLine(c.ProductName + "," + c.TotalPurchase);
}

// si quiere el store procedure solo retorna un valor, esto lo usan para busquedas o totales.

var query = dbNorthwind.ObtenerCategoria(txtcodigo.text).Single();
return query.categoryname;

// otro ejemplo de llamar store procedure con linq
var contactNames =
from result in db.GetCustomersInCity("London")
select result.ContactName;


foreach (string contactName in contactNames)
{
Console.WriteLine(contactName) ;
}

Las transacciones tambien son soportadas en linq ejemplo:

using(TransactionScope ts = new TransactionScope())
{
db.ExecuteCommand("exec sp_DoSomethingCool");
db.SubmitChanges();
ts.Complete();
}

alternativa:

db.LocalTransaction = db.Connection.BeginTransaction();
{
db.SubmitChanges();
db.LocalTransaction.Commit();
db.AcceptChanges();
}
catch {
db.LocalTransaction.Abort();
throw;
}
finally {
db.LocalTransaction = null;
}


si quiere manejar la concurecnia en este punto, puede guiarse con el siguiente ejemplo:
db.SubmitChanges(ConflictMode.FailOnFirstConflict);
db.SubmitChanges(ConflictMode.ContinueOnConflict);




si quieren usar LINQ con Listas
var custOrders =
from c in db.Customers
join o in db.Orders on c.CustomerID equals o.CustomerID into orders
where c.CustomerID == "ALFKI"
select new {c.ContactName, orders};

var list = custOrders.ToList() ;

foreach (var listItem in list)
{
Console.WriteLine(listItem.ContactName + " has " + listItem.orders.Count() + " orders, which have been shipped to:") ;
foreach (Order order in listItem.orders)
{
Console.WriteLine(" Order shipped to - " + order.ShipCountry) ;
}
}



Listas genericas


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
public static void Main() {
List customers = GetCustomerList();
var waCustomers =
from c in customers
where c.Region == "R1"
select c;
foreach (var customer in waCustomers) {
Console.WriteLine("Customer {0}: {1}", customer.CustomerId, customer.CompanyName);
foreach (var order in customer.Orders) {
Console.WriteLine(" Order {0}: {1}", order.Id, order.OrderDate);
}
}
}
static List GetCustomerList() {
List empTree = new List();
empTree.Add(new Product { ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });

List l = new List();
l.Add(new Customer { CompanyName = "A", Region = "R1", UnitsInStock = 1, Orders = empTree, CustomerId =0});
l.Add(new Customer { CompanyName = "B", Region = "R2", UnitsInStock = 2, Orders = empTree, CustomerId = 1 });
l.Add(new Customer { CompanyName = "C", Region = "R3", UnitsInStock = 3, Orders = empTree, CustomerId = 2 });
l.Add(new Customer { CompanyName = "D", Region = "R4", UnitsInStock = 4, Orders = empTree, CustomerId = 3 });
l.Add(new Customer { CompanyName = "E", Region = "R5", UnitsInStock = 5, Orders = empTree, CustomerId = 4 });
return l;
}
}

class Customer : IComparable {
public string CompanyName { get; set; }
public string Region { get; set; }
public List Orders { get; set; }
public int UnitsInStock { get; set; }
public int CustomerId { get; set; }

public override string ToString() {
return String.Format("Id: {0}, Name: {1}, Region: {3}", this.CustomerId, this.CompanyName, this.Region);
}
int IComparable.CompareTo(Customer other) {
if (other == null)
return 1;

if (this.CustomerId > other.CustomerId)
return 1;

if (this.CustomerId < other.CustomerId) return -1; return 0; } } class Product : IComparable {
public string ProductName { get; set; }
public string Category { get; set; }
public int UnitPrice { get; set; }
public int UnitsInStock { get; set; }
public int Total { get; set; }
public DateTime OrderDate { get; set; }
public int Id { get; set; }

public override string ToString() {
return String.Format("Id: {0}, Name: {1} , Category: {3}", this.Id, this.ProductName, this.Category);
}
int IComparable.CompareTo(Product other) {
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;

if (this.Id < other.Id) return -1; return 0; } } http://www.java2s.com/Code/CSharp/LINQ/Useforeachlooptodealwiththeresultfromlinq.htm