Huangzj
142 lines
4.5 KiB
Markdown
142 lines
4.5 KiB
Markdown
# go-linq [](https://godoc.org/github.com/ahmetalpbalkan/go-linq) [](https://travis-ci.org/ahmetalpbalkan/go-linq) [](https://coveralls.io/github/ahmetalpbalkan/go-linq?branch=master) [](https://goreportcard.com/report/github.com/ahmetalpbalkan/go-linq)
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A powerful language integrated query (LINQ) library for Go.
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* Written in vanilla Go!
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* Safe for concurrent use
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* Complete lazy evaluation with iterator pattern
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* Supports arrays, slices, maps, strings, channels and custom collections
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(collection needs to implement `Iterable` interface and element - `Comparable`
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interface)
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## Installation
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$ go get github.com/ahmetalpbalkan/go-linq
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> :warning: :warning: `go-linq` has recently introduced _breaking API changes_
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> with v2.0.0. See [release notes](#release-notes) for details. v2.0.0 comes with
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> a refined interface, dramatically increased performance and memory efficiency,
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> and new features such as lazy evaluation ([read more](http://kalan.rocks/2016/07/16/manipulating-data-with-iterators-in-go/)).
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>
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> The old version is still available in `archive/0.9` branch and tagged as `0.9`
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> as well. If you are using `go-linq`, please vendor a copy of it in your
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> source tree to avoid getting broken by upstream changes.
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## Quickstart
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Usage is as easy as chaining methods like:
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`From(slice)` `.Where(predicate)` `.Select(selector)` `.Union(data)`
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**Example: Find all owners of cars manufactured from 2015**
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```go
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import . "github.com/ahmetalpbalkan/go-linq"
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type Car struct {
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id, year int
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owner, model string
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}
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owners := []string{}
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From(cars).Where(func(c interface{}) bool {
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return c.(Car).year >= 2015
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}).Select(func(c interface{}) interface{} {
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return c.(Car).owner
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}).ToSlice(&owners)
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```
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**Example: Find the author who has written the most books**
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```go
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import . "github.com/ahmetalpbalkan/go-linq"
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type Book struct {
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id int
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title string
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authors []string
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}
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author := From(books).SelectMany( // make a flat array of authors
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func(book interface{}) Query {
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return From(book.(Book).authors)
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}).GroupBy( // group by author
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func(author interface{}) interface{} {
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return author // author as key
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}, func(author interface{}) interface{} {
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return author // author as value
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}).OrderByDescending( // sort groups by its length
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func(group interface{}) interface{} {
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return len(group.(Group).Group)
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}).Select( // get authors out of groups
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func(group interface{}) interface{} {
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return group.(Group).Key
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}).First() // take the first author
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```
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**Example: Implement a custom method that leaves only values greater than the specified threshold**
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```go
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type MyQuery Query
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func (q MyQuery) GreaterThan(threshold int) Query {
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return Query{
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Iterate: func() Iterator {
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next := q.Iterate()
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return func() (item interface{}, ok bool) {
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for item, ok = next(); ok; item, ok = next() {
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if item.(int) > threshold {
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return
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}
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}
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return
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}
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},
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}
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}
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result := MyQuery(Range(1,10)).GreaterThan(5).Results()
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```
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**More examples** can be found in [documentation](https://godoc.org/github.com/ahmetalpbalkan/go-linq).
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## Release Notes
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~~~
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v2.0.0 (2016-09-02)
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* IMPORTANT: This release is a BREAKING CHANGE. The old version
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is archived at the 'archive/0.9' branch or the 0.9 tags.
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* A COMPLETE REWRITE of go-linq with better performance and memory
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efficiency. (thanks @kalaninja!)
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* API has significantly changed. Most notably:
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- linq.T removed in favor of interface{}
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- library methods no longer return errors
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- PLINQ removed for now (see channels support)
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- support for channels, custom collections and comparables
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v0.9-rc4
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* GroupBy()
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v0.9-rc3.2
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* bugfix: All() iterating over values instead of indices
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v0.9-rc3.1
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* bugfix: modifying result slice affects subsequent query methods
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v0.9-rc3
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* removed FirstOrNil, LastOrNil, ElementAtOrNil methods
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v0.9-rc2.5
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* slice-accepting methods accept slices of any type with reflections
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v0.9-rc2
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* parallel linq (plinq) implemented
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* Queryable separated into Query & ParallelQuery
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* fixed early termination for All
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v0.9-rc1
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* many linq methods are implemented
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* methods have error handling support
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* type assertion limitations are unresolved
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* travis-ci.org build integrated
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* open sourced on github, master & dev branches
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~~~
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