# linq4j

**Repository Path**: August08/linq4j

## Basic Information

- **Project Name**: linq4j
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: Apache-2.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2018-01-26
- **Last Updated**: 2020-12-19

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

[![Build Status](https://travis-ci.org/julianhyde/linq4j.png)](https://travis-ci.org/julianhyde/linq4j)

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
* <a href="HISTORY.md">Release notes and history</a>