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.
*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 '\\'.
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`.
## Get multiple values at once
The `GetMany` function can be used to get multiple values at the same time.
*These benchmarks were run on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.8 and can be found [here](https://github.com/tidwall/gjson-benchmarks).*
