Similar features of LINQ [closed]

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Closed 9 years ago.

开发者_JAVA技巧 Improve this question

Is there any feature similar to LINQ (.NET) in different languages like JAVA, PHP, etc?

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There are many languages that have syntax or library functions for operating on sequences of objects in a mostly functional way. For example Python has lambda functions, list comprehensions, generators, and the itertools module.

However I don't know of any language that can get anywhere near everything that LINQ can do as cleanly and concisely. Remember that LINQ is not just a way to operate on in-memory structures - LINQ has many providers that share a similar interface:

• LINQ to Objects
• LINQ to XML
• LINQ to SQL
• etc..

Microsoft have done a good job with LINQ. I am sure some other languages will take inspiration from the success of LINQ and consider how to add similar features in the near future.

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Scala has for-comprehensions that provide similar functionality as the LINQ.

Example: Find all attendees with name Fred that speak Danish.

C#:

var xs = 
  from att in attendees
  where att.name == "Fred"
  from lang in att.spokenLanguages
  where lang == "Danish"
  select att;

Scala:

val xs = for {
  att <- attendees
  if att.name == "Fred"
  lang <- att.spokenLanguages
  if lang == "Danish"
} yield att

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Im really surprised that nobody has talked about it, but I've used a port of LINQ to PHP from Martin Balliauw, which works kinda nice. It works kinda well, you can do something like this:

$result = from('$employee')
    ->in( $employeeTable )
    ->where('$employee => strlen($employee->Name) < 5')
    ->orderBy('$employee->Name')
    ->select('$employee');

I even wrote a small blog post about it.

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This is valid Java, but needs this library: https://github.com/nicholas22/jpropel-light

import java.util.Arrays;
import lombok.ExtensionMethod;
import lombok.val;
import propel.core.utils.Linq;
import static propel.core.functional.predicates.Predicates.*;
import static propel.core.functional.projections.Projections.*;

@ExtensionMethod({Linq.class})
public class Main
{

  /**
   * @param args
   */
  public static void main(String[] args)
  {
    val names = new String[] { "john", "james", "john", "eddie" }.where(startsWith("j")).distinct();    
    System.out.println(Arrays.toString(names));

    // prints "[john, james]"
  }
}

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While basic LINQ features, like Select (map) and Where (filter) are present in almost all contemporary programming languages, constructing SQL "on the fly" and lazily is a work for ORM

For example, Django ORM allow you to use such syntax for making a query:

Posts.objects.filter(user=peter).annotate(comment_count=Count('comment')).order_by('comment_count')

It's something like (not very sure) in LINQ:

from p in posts
where p.user == peter
select new { post = p, comment_count = comments.Where(c => c.post == p).Count() }
order by comment_count

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Sure there are, but php is a programming language and not a framework like .net framework. So if you want to use features, you should download some libraries, orms or frameworks to get higher effectivity. I dont think that php has that powerful feature, that could be an equivalent of linq.

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http://code.google.com/p/phpreboot/ implements LINQ partially in a PHP-like language.