LINQ

Java Streams Preview vs .Net LINQ

I’ve started following this very promising blog by the “Geeks From Paradise”. Apart from the fact that I’m a bit envious of geeks living in Costa Rica, this comparison of the upcoming Java 8 Streams API with various of .NET’s LINQ API capabilities is a very interesting read.

A preview of what you’ll find there (just one of 19 examples):

LINQ

List<string> nameList1 = new List(){ 
  "Anders", "David", "James",
  "Jeff", "Joe", "Erik" };
nameList1.Select(c => "Hello! " + c).ToList()
         .ForEach(c => Console.WriteLine(c));

Java Streams

List<String> nameList1 = asList(
  "Anders", "David", "James",
  "Jeff", "Joe", "Erik");
nameList1.stream()
     .map(c -> "Hello! " + c)
     .forEach(System.out::println);

Read the full blog post here:
Java Streams Preview vs .Net High-Order Programming with LINQ

Will Java add LINQ to EL 3.0 in JSR-341?

This fact has somehow slipped by me unnoticed so far: As the JSR-341 websites claim, Java is going to add full .NET-Style LINQ support to its expression language 3.0!

While the JSR-341 website doesn’t explicitly mention these feature additions to the expression language, a lot of details can be seen here:
http://java.net/projects/el-spec/pages/CollectionOperations

This is very interesting, and raises a lot of questions:

  • Is Microsoft on board – i.e. are they part of the expert group?
  • Will Microsoft surrender / sell their LINQ-related patents to Oracle?
  • … or will Oracle challenge those patents?
  • Why would LINQ be added to the EL before it is added to the platform?

Anyway, the mailing lists don’t seem very active and the draft specs is still in a rather early stage. We’ll see where this goes, but this is clearly an addition that I will follow closely in the future!

See also my previous blog post on the subject

jOOQ’s Reason for Being

The below paragraphs were taken from the jOOQ preface from the manual. It is worth thinking about why you should (or should not) use jOOQ in a given project. Specifically, you might be choosing between jOOQ and JPA, jOOQ and Hibernate, or jOOQ and SLICK (in a Scala context). here’s some guidance (slightly biased towards jOOQ, of course…):

jOOQ’s reason for being – compared to JPA

Java and SQL have come a long way. SQL is an “ancient”, yet established and well-understood technology. Java is a legacy too, although its platform JVM allows for many new and contemporary languages built on top of it. Yet, after all these years, libraries dealing with the interface between SQL and Java have come and gone, leaving JPA to be a standard that is accepted only with doubts, short of any surviving options.

So far, there had been only few database abstraction frameworks or libraries, that truly respected SQL as a first class citizen among languages. Most frameworks, including the industry standards JPA, EJB, Hibernate, JDO, Criteria Query, and many others try to hide SQL itself, minimising its scope to things called JPQL, HQL, JDOQL and various other inferior query languages

jOOQ has come to fill this gap.

jOOQ’s reason for being – compared to LINQ

Other platforms incorporate ideas such as LINQ (with LINQ-to-SQL), or Scala’s SLICK to better integrate querying as a concept into their respective language. By querying, they understand querying of arbitrary targets, such as SQL, XML, Collections and other heterogeneous data stores. jOOQ claims that this is going the wrong way too.

In more advanced querying use-cases (more than simple CRUD and the occasional JOIN), people will want to profit from the expressivity of SQL. Due to the relational nature of SQL, this is quite different from what object-oriented and partially functional languages such as C#, Scala, or Java can offer.

It is very hard to formally express and validate joins and the ad-hoc table expression types they create. It gets even harder when you want support for more advanced table expressions, such as pivot tables, unnested cursors, or just arbitrary projections from derived tables. With a very strong object-oriented typing model, these features will probably stay out of scope.

In essence, the decision of creating an API that looks like SQL or one that looks like C#, Scala, Java is a definite decision in favour of one or the other platform. While it will be easier to evolve SLICK in similar ways as LINQ, SQL feature scope that clearly communicates its underlying intent will be very hard to add, later on (e.g. how would you model Oracle’s partitioned outer join syntax? How would you model ANSI/ISO SQL:1999 grouping sets? How can you support scalar subquery caching? etc…).

jOOQ has come to fill this gap.

jOOQ is different

SQL was never meant to be abstracted. To be confined in the narrow boundaries of heavy mappers, hiding the beauty and simplicity of relational data. SQL was never meant to be object-oriented. SQL was never meant to be anything other than… SQL!

SLICK, integrating SQL into Scala

Now it’s official – even if version numbers are still preceded by a “zero” major release: SLICK has been publicly announced by Typesafe:

SLICK stands for Scala Language-Integrated Connection Kit, which is more or less the Scala equivalent for LINQ-to-SQL. Note that I say LINQ-to-SQL, not LINQ in general, as Scala already has sufficient means of querying collections using the Scala language itself.

Here’s a sample of what SLICK code will look like (taken from the SLICK website):

object Coffees extends Table[(String, Int, Double)]("COFFEES") {
  def name = column[String]("COF_NAME", O.PrimaryKey)
  def supID = column[Int]("SUP_ID")
  def price = column[Double]("PRICE")
  def * = name ~ supID ~ price
}

Coffees.insertAll(
  ("Colombian",         101, 7.99),
  ("Colombian_Decaf",   101, 8.99),
  ("French_Roast_Decaf", 49, 9.99)
)

val q = for {
  c <- Coffees if c.supID === 101
  //                       ^ comparing Rep[Int] to Rep[Int]!
} yield (c.name, c.price)

println(q.selectStatement)

q.foreach { case (n, p) => println(n + ": " + p) }

As you can see, SLICK neatly integrates with Scala’s own syntax. As with LINQ-to-SQL, SLICK’s goal is to

“write your database queries in Scala instead of SQL”

This is quite orthogonal to what jOOQ is aiming for:

“SQL was never meant to be anything other than… SQL!”

As a reminder, see my previous blog post about how jOOQ integrates with Scala, and how you can write almost-SQL queries in Scala using jOOQ against 13 popular databases. It would be interesting to compare the two approaches side-by-side in an independent evaluation, to see the pro’s and con’s of each one, in terms of

  • Developer productivity
  • Maintainability
  • Performance
  • Feature scope
  • etc.

I think it’s time someone made that evaluation. An example can be seen here:

http://stackoverflow.com/questions/10537766/closest-equivalent-to-sqlalchemy-for-java-scala

When will we have LINQ in Java?

LINQ is one of Microsoft’s .NET Framework’s most distinct language features. When it was first introduced to languages such as C#, it required heavy changes to the language specification. Yet, this addition was extremely powerful and probably unequalled by other languages / platforms, such as Java, Scala, etc. Granted, Scala has integrated XML in a similar fashion into its language from the beginning, but that is hardly the same accomplishment. Nowadays, Typesafe developers are developing SLICK – Scala Language Integrated Connection Kit, which has similar ambitions, although the effort spent on it is hardly comparable: one “official” Scala developer against a big Microsoft team. Let alone the potential of getting into patent wars with Microsoft, should SLICK ever become popular.

What does Java have to offer?

There are many attempts of bringing LINQ-like API’s to the Java world, as the following Stack Overflow question shows:

http://stackoverflow.com/questions/1217228/what-is-the-java-equivalent-for-linq

Here’s another newcomer project by Julian Hyde, that I’ve recently discovered:

https://github.com/julianhyde/linq4j

He tried his luck on the lambda-dev mailing list, without any response so far. We’re all eagerly awaiting Java 8 and project lambda with its lambda expressions and extension methods. But when will we be able to catch up with Microsoft’s LINQ? After all, jOOQ, linq4j are “internal domain specific languages”, which are all limited by the expressivity of their host language (see my previous blog post about building domain specific languages in Java).

Java 9 maybe? We can only hope!