349 lines
9.6 KiB
Markdown
349 lines
9.6 KiB
Markdown
<p align="center">
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<img
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src="logo.png"
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width="240" height="78" border="0" alt="GJSON">
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<br>
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<a href="https://travis-ci.org/tidwall/gjson"><img src="https://img.shields.io/travis/tidwall/gjson.svg?style=flat-square" alt="Build Status"></a><!--
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<a href="http://gocover.io/github.com/tidwall/gjson"><img src="https://img.shields.io/badge/coverage-97%25-brightgreen.svg?style=flat-square" alt="Code Coverage"></a>
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-->
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<a href="https://godoc.org/github.com/tidwall/gjson"><img src="https://img.shields.io/badge/api-reference-blue.svg?style=flat-square" alt="GoDoc"></a>
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</p>
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<p align="center">get a json value quickly</a></p>
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GJSON is a Go package the provides a [very fast](#performance) and simple way to get a value from a json document. The reason for this library it to give efficient json indexing for the [BuntDB](https://github.com/tidwall/buntdb) project.
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For a command line interface check out [JSONed](https://github.com/tidwall/jsoned).
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Getting Started
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===============
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## Installing
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To start using GJSON, install Go and run `go get`:
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```sh
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$ go get -u github.com/tidwall/gjson
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```
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This will retrieve the library.
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## Get a value
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Get searches json for the specified path. A path is in dot syntax, such as "name.last" or "age". This function expects that the json is well-formed and validates. Invalid json will not panic, but it may return back unexpected results. When the value is found it's returned immediately.
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```go
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package main
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import "github.com/tidwall/gjson"
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const json = `{"name":{"first":"Janet","last":"Prichard"},"age":47}`
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func main() {
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value := gjson.Get(json, "name.last")
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println(value.String())
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}
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```
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This will print:
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```
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Prichard
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```
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*There's also the [GetMany](#get-multiple-values-at-once) function to get multiple values at once, and [GetBytes](#working-with-bytes) for working with JSON byte slices.*
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## Path Syntax
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A path is a series of keys separated by a dot.
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A key may contain special wildcard characters '\*' and '?'.
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To access an array value use the index as the key.
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To get the number of elements in an array or to access a child path, use the '#' character.
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The dot and wildcard characters can be escaped with '\'.
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```json
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{
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"name": {"first": "Tom", "last": "Anderson"},
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"age":37,
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"children": ["Sara","Alex","Jack"],
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"fav.movie": "Deer Hunter",
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"friends": [
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{"first": "James", "last": "Murphy"},
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{"first": "Roger", "last": "Craig"}
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]
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}
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```
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```
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"name.last" >> "Anderson"
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"age" >> 37
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"children" >> ["Sara","Alex","Jack"]
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"children.#" >> 3
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"children.1" >> "Alex"
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"child*.2" >> "Jack"
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"c?ildren.0" >> "Sara"
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"fav\.movie" >> "Deer Hunter"
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"friends.#.first" >> ["James","Roger"]
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"friends.1.last" >> "Craig"
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```
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To query an array:
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```
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`friends.#[last="Murphy"].first` >> "James"
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```
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## Result Type
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GJSON supports the json types `string`, `number`, `bool`, and `null`.
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Arrays and Objects are returned as their raw json types.
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The `Result` type holds one of these:
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```
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bool, for JSON booleans
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float64, for JSON numbers
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string, for JSON string literals
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nil, for JSON null
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```
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To directly access the value:
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```go
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result.Type // can be String, Number, True, False, Null, or JSON
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result.Str // holds the string
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result.Num // holds the float64 number
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result.Raw // holds the raw json
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result.Index // index of raw value in original json, zero means index unknown
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```
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There are a variety of handy functions that work on a result:
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```go
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result.Value() interface{}
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result.Int() int64
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result.Uint() uint64
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result.Float() float64
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result.String() string
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result.Bool() bool
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result.Array() []gjson.Result
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result.Map() map[string]gjson.Result
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result.Get(path string) Result
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```
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The `result.Value()` function returns an `interface{}` which requires type assertion and is one of the following Go types:
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The `result.Array()` function returns back an array of values.
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If the result represents a non-existent value, then an empty array will be returned.
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If the result is not a JSON array, the return value will be an array containing one result.
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```go
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boolean >> bool
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number >> float64
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string >> string
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null >> nil
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array >> []interface{}
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object >> map[string]interface{}
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```
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## Get nested array values
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Suppose you want all the last names from the following json:
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```json
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{
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"programmers": [
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{
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"firstName": "Janet",
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"lastName": "McLaughlin",
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}, {
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"firstName": "Elliotte",
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"lastName": "Hunter",
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}, {
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"firstName": "Jason",
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"lastName": "Harold",
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}
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]
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}`
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```
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You would use the path "programmers.#.lastName" like such:
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```go
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result := gjson.Get(json, "programmers.#.lastName")
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for _,name := range result.Array() {
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println(name.String())
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}
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```
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You can also query an object inside an array:
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```go
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name := gjson.Get(json, `programmers.#[lastName="Hunter"].firstName`)
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println(name.String()) // prints "Elliotte"
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```
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## Simple Parse and Get
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There's a `Parse(json)` function that will do a simple parse, and `result.Get(path)` that will search a result.
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For example, all of these will return the same result:
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```go
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gjson.Parse(json).Get("name").Get("last")
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gjson.Get(json, "name").Get("last")
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gjson.Get(json, "name.last")
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```
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## Check for the existence of a value
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Sometimes you just want to know if a value exists.
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```go
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value := gjson.Get(json, "name.last")
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if !value.Exists() {
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println("no last name")
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} else {
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println(value.String())
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}
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// Or as one step
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if gjson.Get(json, "name.last").Exists(){
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println("has a last name")
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}
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```
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## Unmarshal to a map
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To unmarshal to a `map[string]interface{}`:
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```go
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m, ok := gjson.Parse(json).Value().(map[string]interface{})
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if !ok{
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// not a map
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}
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```
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## Working with Bytes
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If your JSON is contained in a `[]byte` slice, there's the [GetBytes](https://godoc.org/github.com/tidwall/gjson#GetBytes) function. This is preferred over `Get(string(data), path)`.
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```go
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var json []byte = ...
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result := gjson.GetBytes(json, path)
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```
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If you are using the `gjson.GetBytes(json, path)` function and you want to avoid converting `result.Raw` to a `[]byte`, then you can use this pattern:
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```go
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var json []byte = ...
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result := gjson.GetBytes(json, path)
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var raw []byte
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if result.Index > 0 {
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raw = json[result.Index:result.Index+len(result.Raw)]
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} else {
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raw = []byte(result.Raw)
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}
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```
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This is a best-effort no allocation sub slice of the original json. This method utilizes the `result.Index` field, which is the position of the raw data in the original json. It's possible that the value of `result.Index` equals zero, in which case the `result.Raw` is converted to a `[]byte`.
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## Get multiple values at once
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The `GetMany` function can be used to get multiple values at the same time, and is optimized to scan over a JSON payload once.
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```go
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results := gjson.GetMany(json, "name.first", "name.last", "age")
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```
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The return value is a `[]Result`, which will always contain exactly the same number of items as the input paths.
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## Performance
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Benchmarks of GJSON alongside [encoding/json](https://golang.org/pkg/encoding/json/),
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[ffjson](https://github.com/pquerna/ffjson),
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[EasyJSON](https://github.com/mailru/easyjson),
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and [jsonparser](https://github.com/buger/jsonparser)
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```
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BenchmarkGJSONGet-8 15000000 333 ns/op 0 B/op 0 allocs/op
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BenchmarkGJSONUnmarshalMap-8 900000 4188 ns/op 1920 B/op 26 allocs/op
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BenchmarkJSONUnmarshalMap-8 600000 8908 ns/op 3048 B/op 69 allocs/op
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BenchmarkJSONUnmarshalStruct-8 600000 9026 ns/op 1832 B/op 69 allocs/op
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BenchmarkJSONDecoder-8 300000 14339 ns/op 4224 B/op 184 allocs/op
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BenchmarkFFJSONLexer-8 1500000 3156 ns/op 896 B/op 8 allocs/op
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BenchmarkEasyJSONLexer-8 3000000 938 ns/op 613 B/op 6 allocs/op
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BenchmarkJSONParserGet-8 3000000 442 ns/op 21 B/op 0 allocs/op
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```
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Benchmarks for the `GetMany` function:
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```
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BenchmarkGJSONGetMany4Paths-8 4000000 319 ns/op 112 B/op 0 allocs/op
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BenchmarkGJSONGetMany8Paths-8 8000000 218 ns/op 56 B/op 0 allocs/op
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BenchmarkGJSONGetMany16Paths-8 16000000 160 ns/op 56 B/op 0 allocs/op
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BenchmarkGJSONGetMany32Paths-8 32000000 130 ns/op 64 B/op 0 allocs/op
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BenchmarkGJSONGetMany64Paths-8 64000000 117 ns/op 64 B/op 0 allocs/op
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BenchmarkGJSONGetMany128Paths-8 128000000 109 ns/op 64 B/op 0 allocs/op
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```
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JSON document used:
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```json
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{
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"widget": {
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"debug": "on",
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"window": {
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"title": "Sample Konfabulator Widget",
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"name": "main_window",
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"width": 500,
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"height": 500
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},
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"image": {
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"src": "Images/Sun.png",
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"hOffset": 250,
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"vOffset": 250,
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"alignment": "center"
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},
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"text": {
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"data": "Click Here",
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"size": 36,
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"style": "bold",
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"vOffset": 100,
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"alignment": "center",
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"onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
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}
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}
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}
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```
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Each operation was rotated though one of the following search paths:
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```
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widget.window.name
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widget.image.hOffset
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widget.text.onMouseUp
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```
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For the `GetMany` benchmarks these paths are used:
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```
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widget.window.name
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widget.image.hOffset
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widget.text.onMouseUp
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widget.window.title
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widget.image.alignment
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widget.text.style
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widget.window.height
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widget.image.src
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widget.text.data
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widget.text.size
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```
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*These benchmarks were run on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.7.*
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## Contact
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Josh Baker [@tidwall](http://twitter.com/tidwall)
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## License
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GJSON source code is available under the MIT [License](/LICENSE).
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