linq4j

A port of LINQ (Language-Integrated Query) to Java.

Download

$ git clone git://github.com/julianhyde/linq4j.git linq4j

Build and test

$ mvn package

Backlog

If you would like to contribute, here are some of the tasks we have planned. Please let us know if you are starting one.

• Implement and test the methods allowing queries on Enumerables. The methods are specified in ExtendedEnumerable, DefaultEnumerable calls the implementations in Extensions. We'll do these in tranches. Each time you implement a method, add a test similar to Linq4jTest.testWhere. Try to refactor out some helper (named inner) classes, rather than creating 2 or 3 anonymous classes per method.

• Third tranche: implement groupBy for Enumerable.

• Fourth tranche: implement any, all, aggregate, sum, min, max, average for Enumerable.

• Sixth tranche: implement union, intersect, except, distinct methods for Enumerable.

• Seventh tranche: first, last, defaultIfEmpty, elementAtOrDefault, firstOrDefault, lastOrDefault for Enumerable. May need to add a class parameter so that we can generate the right default value.

• Eighth tranche: implement orderBy, reverse for Enumerable.

• Ninth tranche: implement methods that require EqualityComparer.

• Last tranche: all remaining methods for Enumerable.

• Parser support. Either modify a Java parser (e.g. OpenJDK), or write a pre-processor. Generate Java code that includes expression trees.

• Port Enumerable and Queryable to Scala. Change classes (in particular, collections and function types) so that user code is looks like concise, native Scala. Share as much of the back-end as possible with linq4j, but don't compromise the Scala look-and-feel of the front-end. Use adapters (and sacrifice a bit of performance) if it helps.

• Write a simple LINQ-to-SQL provider. This would generate SQL and get data from JDBC. It's a prototype, demonstrating that we can connect the dots. Plan to throw it away.

• In the prototype LINQ-to-SQL provider, write a simple rule to recognize a select list and where clause and push them down to SQL.

• Test Scala front-end against LINQ-to-SQL provider.

• A better provider using a planner framework.

• JDBC driver on top of linq4j (not necessarily on top of the Queryable/Expression object model; more likely on the query model that this translates to).

• Use planner framework to build back-ends to non-SQL data sources (e.g. MongoDB, Hadoop, text files).

Already implemented

Methods on Enumerable:

• select, selectMany, where, groupJoin, join;
• count, longCount;
• cast, ofType;
• toMap, toLookup, skip, skipWhile, take, takeWhile.

Methods on Queryable:

• where, whereN
• skip, skipWhile, skipWhileN, take, takeWhile, takeWhileN.

(Except methods that involve EqualityComparer.)

More information

• License: Apache License, Version 2.0.
• Author: Julian Hyde
• Blog: http://julianhyde.blogspot.com
• Project page: http://www.hydromatic.net/linq4j
• Source code: http://github.com/julianhyde/linq4j
• Developers list: http://groups.google.com/group/linq4j-dev
• Release notes and history