GJSON is a Go package that provides a [fast](#performance) and [simple](#get-a-value) way to get values from a json document.
It has features such as [one line retrieval](#get-a-value), [dot notation paths](#path-syntax), [iteration](#iterate-through-an-object-or-array), and [parsing json lines](#json-lines).
Also check out [SJSON](https://github.com/tidwall/sjson) for modifying json, and the [JJ](https://github.com/tidwall/jj) command line tool.
This README is a quick overview of how to use GJSON, for more information check out [GJSON Syntax](SYNTAX.md).
GJSON is also available for [Python](https://github.com/volans-/gjson-py) and [Rust](https://github.com/tidwall/gjson.rs)
Getting Started
===============
## Installing
To start using GJSON, install Go and run `go get`:
```sh
$ go get -u github.com/tidwall/gjson
```
This will retrieve the library.
## Get a value
Get searches json for the specified path. A path is in dot syntax, such as "name.last" or "age". When the value is found it's returned immediately.
*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.*
## Path Syntax
Below is a quick overview of the path syntax, for more complete information please
check out [GJSON Syntax](SYNTAX.md).
A path is a series of keys separated by a dot.
A key may contain special wildcard characters '\*' and '?'.
To access an array value use the index as the key.
To get the number of elements in an array or to access a child path, use the '#' character.
The dot and wildcard characters can be escaped with '\\'.
The `result.Value()` function returns an `interface{}` which requires type assertion and is one of the following Go types:
```go
boolean >> bool
number >> float64
string >> string
null >> nil
array >> []interface{}
object >> map[string]interface{}
```
The `result.Array()` function returns back an array of values.
If the result represents a non-existent value, then an empty array will be returned.
If the result is not a JSON array, the return value will be an array containing one result.
### 64-bit integers
The `result.Int()` and `result.Uint()` calls are capable of reading all 64 bits, allowing for large JSON integers.
```go
result.Int() int64 // -9223372036854775808 to 9223372036854775807
result.Uint() uint64 // 0 to 18446744073709551615
```
## Modifiers and path chaining
New in version 1.2 is support for modifier functions and path chaining.
A modifier is a path component that performs custom processing on the
json.
Multiple paths can be "chained" together using the pipe character.
This is useful for getting results from a modified query.
For example, using the built-in `@reverse` modifier on the above json document,
we'll get `children` array and reverse the order:
```
"children|@reverse" >> ["Jack","Alex","Sara"]
"children|@reverse|0" >> "Jack"
```
There are currently the following built-in modifiers:
-`@reverse`: Reverse an array or the members of an object.
-`@ugly`: Remove all whitespace from a json document.
-`@pretty`: Make the json document more human readable.
-`@this`: Returns the current element. It can be used to retrieve the root element.
-`@valid`: Ensure the json document is valid.
-`@flatten`: Flattens an array.
-`@join`: Joins multiple objects into a single object.
-`@keys`: Returns an array of keys for an object.
-`@values`: Returns an array of values for an object.
-`@tostr`: Converts json to a string. Wraps a json string.
-`@fromstr`: Converts a string from json. Unwraps a json string.
-`@group`: Groups arrays of objects. See [e4fc67c](https://github.com/tidwall/gjson/commit/e4fc67c92aeebf2089fabc7872f010e340d105db).
-`@dig`: Search for a value without providing its entire path. See [e8e87f2](https://github.com/tidwall/gjson/commit/e8e87f2a00dc41f3aba5631094e21f59a8cf8cbf).
### Modifier arguments
A modifier may accept an optional argument. The argument can be a valid JSON
document or just characters.
For example, the `@pretty` modifier takes a json object as its argument.
```
@pretty:{"sortKeys":true}
```
Which makes the json pretty and orders all of its keys.
```json
{
"age":37,
"children": ["Sara","Alex","Jack"],
"fav.movie": "Deer Hunter",
"friends": [
{"age": 44, "first": "Dale", "last": "Murphy"},
{"age": 68, "first": "Roger", "last": "Craig"},
{"age": 47, "first": "Jane", "last": "Murphy"}
],
"name": {"first": "Tom", "last": "Anderson"}
}
```
*The full list of `@pretty` options are `sortKeys`, `indent`, `prefix`, and `width`.
Please see [Pretty Options](https://github.com/tidwall/pretty#customized-output) for more information.*
### Custom modifiers
You can also add custom modifiers.
For example, here we create a modifier that makes the entire json document upper
Suppose you want all the last names from the following json:
```json
{
"programmers": [
{
"firstName": "Janet",
"lastName": "McLaughlin",
}, {
"firstName": "Elliotte",
"lastName": "Hunter",
}, {
"firstName": "Jason",
"lastName": "Harold",
}
]
}
```
You would use the path "programmers.#.lastName" like such:
```go
result := gjson.Get(json, "programmers.#.lastName")
for _, name := range result.Array() {
println(name.String())
}
```
You can also query an object inside an array:
```go
name := gjson.Get(json, `programmers.#(lastName="Hunter").firstName`)
println(name.String()) // prints "Elliotte"
```
## Iterate through an object or array
The `ForEach` function allows for quickly iterating through an object or array.
The key and value are passed to the iterator function for objects.
Only the value is passed for arrays.
Returning `false` from an iterator will stop iteration.
```go
result := gjson.Get(json, "programmers")
result.ForEach(func(key, value gjson.Result) bool {
println(value.String())
return true // keep iterating
})
```
## Simple Parse and Get
There's a `Parse(json)` function that will do a simple parse, and `result.Get(path)` that will search a result.
For example, all of these will return the same result:
```go
gjson.Parse(json).Get("name").Get("last")
gjson.Get(json, "name").Get("last")
gjson.Get(json, "name.last")
```
## Check for the existence of a value
Sometimes you just want to know if a value exists.
```go
value := gjson.Get(json, "name.last")
if !value.Exists() {
println("no last name")
} else {
println(value.String())
}
// Or as one step
if gjson.Get(json, "name.last").Exists() {
println("has a last name")
}
```
## Validate JSON
The `Get*` and `Parse*` functions expects that the json is well-formed. Bad json will not panic, but it may return back unexpected results.
If you are consuming JSON from an unpredictable source then you may want to validate prior to using GJSON.
```go
if !gjson.Valid(json) {
return errors.New("invalid json")
}
value := gjson.Get(json, "name.last")
```
## Unmarshal to a map
To unmarshal to a `map[string]interface{}`:
```go
m, ok := gjson.Parse(json).Value().(map[string]interface{})
if !ok {
// not a map
}
```
## Working with Bytes
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)`.
```go
var json []byte = ...
result := gjson.GetBytes(json, path)
```
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:
```go
var json []byte = ...
result := gjson.GetBytes(json, path)
var raw []byte
if result.Index > 0 {
raw = json[result.Index:result.Index+len(result.Raw)]
} else {
raw = []byte(result.Raw)
}
```
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`.
## Performance
Benchmarks of GJSON alongside [encoding/json](https://golang.org/pkg/encoding/json/),
