Citat:
@deerbeer
Sto znaci da podaci ne moraju uvek biti na sql-u (xml ,user defined class...bilo sta .)
npr. IQueryable<T> , IEnumerable<T>
Svidja mi se kombinovanje template kolekcija i functor klasa za logicke uslove
A evo zasto .... kolko sam uspeo dosad da proucim iz primera:
Kod mozda nije 100% tacan nemam sad kompajler pri ruci :(
Svaka ispravka i komentar je dobrodosao ..
Code:
// npr imam kolekciju contact-a u xml fajlu
<Contacts>
<Contact>
<name></name>
<address></address>
<phone></phone>
</Contact>
....
...
</Contacts>
XElement contacts = XElement.Load(@"c:\myContactList.xml");
IEnumerable<string> query = from c in contacts.Elements("contact")
where (string) c.Element("address").Element("state") == "WA"
orderby (string) c.Element("name")
select (string) c.Element("name");
foreach (c in query) {
Console.WriteLine(c);
}
IEnumerable<XElement> query = from c in contacts.Elements("contact"),
ph in c.Elements("phone")
where (string) c.Element("address").Element("state") == "WA" &&
p h.Value.StartsWith("206")
orderby (string) c.Element("name")
select c;
//vracamo recordset od xml-a
foreach (x in query){
Console.WriteLine(x);
}
Deluje mi skroz super da ne moram da radim query xml-a preko XPath-a
Podsetite se njegove ruzne sintakse ..pogotovu ako ulaze u obzir i neki logicki uslovi
A ovo je mozda glavni benefit od LINQ-a kako kaze MS :
Citat:
The benefit for data source implementers of reusing this deferring functionality by implementing the IQueryable<T> interface is obvious.
To the clients who write the queries, on the other hand, it is a great advantage to have a common type for remote information sources.
Not only does it allow them to write polymorphic queries that can be used against different sources of data,
but it also opens up the possibility for writing queries that go across domains.
Code:
namespace System.Linq {
using System;
using System.Collections.Generic;
public static class Enumerable {
public static IEnumerable<T> Where<T>(
this IEnumerable<T> source,
Func<T, bool> predicate){
foreach (T item in source)
if (predicate(item))
yield return item;
}
}
}
//Ovde je Func<T,bool> kao logicki operator sa bilo kojim tipom ...
string []names = {"Pera","Mika","Laza","Mirko","Slavko" };
Func<string,bool> manjeOd6 = s => s.Length < 6 ;
IEnumerable<string> query = Enumerable.Where(names,manjeOd6);
int [] nizinta = {32,2,34,3,54} ;
Func<int,bool> veceod10 = s => s > 10 ;
IEnumerable<int> query = Enumerable.Where(nizinta,veceod10);
//Ako to sve upakujemo kao funkciju da izgleda kao "SELECT" upit to bi izgledalo
public static IEnumerable <T> Select (IEnumerable<T> source,Func<T,bool> where1,Fucn<T,bool> where2 ..itd...)
//ili mozda jos lepse kao niz Funktora
//ne znam da li ovo dozvoljava c# 3.5 kompajler .
public static IEnumerable <T> Select (IEnumerable<T> source,params Func<T,bool>[] wheres_array) ;
//ako imamo kolekciju objekata
// najbolje je naslediti IQuerable<T> sa kojom dolazi jos mnostvo opcija za expression izraze,agregacije,sorting-om itd .....
public MyQueryEngine<T> : public IQuerable<T>
There's a law for the rich - a law for people like you and me
Fuck the criminal justice bill - Shove it up your ass
Crimes on the increase - They blame the working class
LINQ to SQL - razna pitanja
Re: LINQ to SQL - razna pitanja
