gjson.md 24 KB
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.
package main
import "github.com/tidwall/gjson"
const json = `{"name":{"first":"Janet","last":"Prichard"},"age":47}`
func main() {
value := gjson.Get(json, "name.last")
println(value.String())
}
This will print:
Prichard
There's also the GetMany function to get multiple values at once, and GetBytes 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.
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 '\'.
{
"name": {"first": "Tom", "last": "Anderson"},
"age":37,
"children": ["Sara","Alex","Jack"],
"fav.movie": "Deer Hunter",
"friends": [
{"first": "Dale", "last": "Murphy", "age": 44, "nets": ["ig", "fb", "tw"]},
{"first": "Roger", "last": "Craig", "age": 68, "nets": ["fb", "tw"]},
{"first": "Jane", "last": "Murphy", "age": 47, "nets": ["ig", "tw"]}
]
}
"name.last" >> "Anderson"
"age" >> 37
"children" >> ["Sara","Alex","Jack"]
"children.#" >> 3
"children.1" >> "Alex"
"child*.2" >> "Jack"
"c?ildren.0" >> "Sara"
"fav\.movie" >> "Deer Hunter"
"friends.#.first" >> ["Dale","Roger","Jane"]
"friends.1.last" >> "Craig"
You can also query an array for the first match by using #(...), or find all
matches with #(...)#. Queries support the ==, !=, <, <=, >, >=
comparison operators and the simple pattern matching % (like) and !%
(not like) operators.
friends.#(last=="Murphy").first >> "Dale"
friends.#(last=="Murphy")#.first >> ["Dale","Jane"]
friends.#(age>45)#.last >> ["Craig","Murphy"]
friends.#(first%"D*").last >> "Murphy"
friends.#(first!%"D*").last >> "Craig"
friends.#(nets.#(=="fb"))#.first >> ["Dale","Roger"]
Please note that prior to v1.3.0, queries used the #[...] brackets. This was
changed in v1.3.0 as to avoid confusion with the new
multipath syntax. For backwards compatibility,
#[...] will continue to work until the next major release.
Result Type
GJSON supports the json types string, number, bool, and null.
Arrays and Objects are returned as their raw json types.
The Result type holds one of these:
bool, for JSON booleans
float64, for JSON numbers
string, for JSON string literals
nil, for JSON null
To directly access the value:
result.Type // can be String, Number, True, False, Null, or JSON
result.Str // holds the string
result.Num // holds the float64 number
result.Raw // holds the raw json
result.Index // index of raw value in original json, zero means index unknown
result.Indexes // indexes of all the elements that match on a path containing the '#' query character.
There are a variety of handy functions that work on a result:
result.Exists() bool
result.Value() interface{}
result.Int() int64
result.Uint() uint64
result.Float() float64
result.String() string
result.Bool() bool
result.Time() time.Time
result.Array() []gjson.Result
result.Map() map[string]gjson.Result
result.Get(path string) Result
result.ForEach(iterator func(key, value Result) bool)
result.Less(token Result, caseSensitive bool) bool
The result.Value() function returns an interface{} which requires type assertion and is one of the following Go types:
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.
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.@dig: Search for a value without providing its entire path. See e8e87f2.
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.
{
"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 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 or lower case.
gjson.AddModifier("case", func(json, arg string) string {
if arg == "upper" {
return strings.ToUpper(json)
}
if arg == "lower" {
return strings.ToLower(json)
}
return json
})
"children|@case:upper" >> ["SARA","ALEX","JACK"]
"children|@case:lower|@reverse" >> ["jack","alex","sara"]
JSON Lines
There's support for JSON Lines using the .. prefix, which treats a multilined document as an array.
For example:
{"name": "Gilbert", "age": 61}
{"name": "Alexa", "age": 34}
{"name": "May", "age": 57}
{"name": "Deloise", "age": 44}
..# >> 4
..1 >> {"name": "Alexa", "age": 34}
..3 >> {"name": "Deloise", "age": 44}
..#.name >> ["Gilbert","Alexa","May","Deloise"]
..#(name="May").age >> 57
The ForEachLines function will iterate through JSON lines.
gjson.ForEachLine(json, func(line gjson.Result) bool{
println(line.String())
return true
})
Get nested array values
Suppose you want all the last names from the following json:
{
"programmers": [
{
"firstName": "Janet",
"lastName": "McLaughlin",
}, {
"firstName": "Elliotte",
"lastName": "Hunter",
}, {
"firstName": "Jason",
"lastName": "Harold",
}
]
}
You would use the path "programmers.#.lastName" like such:
result := gjson.Get(json, "programmers.#.lastName")
for _, name := range result.Array() {
println(name.String())
}
You can also query an object inside an array:
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.
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:
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.
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.
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{}:
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 function. This is preferred over Get(string(data), path).
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:
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, ffjson, EasyJSON, jsonparser, and json-iterator
BenchmarkGJSONGet-16 11644512 311 ns/op 0 B/op 0 allocs/op
BenchmarkGJSONUnmarshalMap-16 1122678 3094 ns/op 1920 B/op 26 allocs/op
BenchmarkJSONUnmarshalMap-16 516681 6810 ns/op 2944 B/op 69 allocs/op
BenchmarkJSONUnmarshalStruct-16 697053 5400 ns/op 928 B/op 13 allocs/op
BenchmarkJSONDecoder-16 330450 10217 ns/op 3845 B/op 160 allocs/op
BenchmarkFFJSONLexer-16 1424979 2585 ns/op 880 B/op 8 allocs/op
BenchmarkEasyJSONLexer-16 3000000 729 ns/op 501 B/op 5 allocs/op
BenchmarkJSONParserGet-16 3000000 366 ns/op 21 B/op 0 allocs/op
BenchmarkJSONIterator-16 3000000 869 ns/op 693 B/op 14 allocs/op
JSON document used:
{
"widget": {
"debug": "on",
"window": {
"title": "Sample Konfabulator Widget",
"name": "main_window",
"width": 500,
"height": 500
},
"image": {
"src": "Images/Sun.png",
"hOffset": 250,
"vOffset": 250,
"alignment": "center"
},
"text": {
"data": "Click Here",
"size": 36,
"style": "bold",
"vOffset": 100,
"alignment": "center",
"onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
}
}
}
Each operation was rotated through one of the following search paths:
widget.window.name
widget.image.hOffset
widget.text.onMouseUp
These benchmarks were run on a MacBook Pro 16" 2.4 GHz Intel Core i9 using Go 1.17 and can be found here.
GJSON Path Syntax
A GJSON Path is a text string syntax that describes a search pattern for quickly retreiving values from a JSON payload.
This document is designed to explain the structure of a GJSON Path through examples.
- Path structure
- Basic
- Wildcards
- Escape Character
- Arrays
- Queries
- Dot vs Pipe
- Modifiers
- Multipaths
- Literals
The definitive implemenation is github.com/tidwall/gjson.
Use the GJSON Playground to experiment with the syntax online.
Path structure
A GJSON Path is intended to be easily expressed as a series of components seperated by a . character.
Along with . character, there are a few more that have special meaning, including |, #, @, \, *, !, and ?.
Example
Given this JSON
{
"name": {"first": "Tom", "last": "Anderson"},
"age":37,
"children": ["Sara","Alex","Jack"],
"fav.movie": "Deer Hunter",
"friends": [
{"first": "Dale", "last": "Murphy", "age": 44, "nets": ["ig", "fb", "tw"]},
{"first": "Roger", "last": "Craig", "age": 68, "nets": ["fb", "tw"]},
{"first": "Jane", "last": "Murphy", "age": 47, "nets": ["ig", "tw"]}
]
}
The following GJSON Paths evaluate to the accompanying values.
Basic
In many cases you'll just want to retreive values by object name or array index.
name.last "Anderson"
name.first "Tom"
age 37
children ["Sara","Alex","Jack"]
children.0 "Sara"
children.1 "Alex"
friends.1 {"first": "Roger", "last": "Craig", "age": 68}
friends.1.first "Roger"
Wildcards
A key may contain the special wildcard characters * and ?.
The * will match on any zero+ characters, and ? matches on any one character.
child*.2 "Jack"
c?ildren.0 "Sara"
Escape character
Special purpose characters, such as ., *, and ? can be escaped with \.
fav\.movie "Deer Hunter"
You'll also need to make sure that the \ character is correctly escaped when hardcoding a path in your source code.
// Go
val := gjson.Get(json, "fav\\.movie") // must escape the slash
val := gjson.Get(json, `fav\.movie`) // no need to escape the slash
// Rust
let val = gjson::get(json, "fav\\.movie") // must escape the slash
let val = gjson::get(json, r#"fav\.movie"#) // no need to escape the slash
Arrays
The # character allows for digging into JSON Arrays.
To get the length of an array you'll just use the # all by itself.
friends.# 3
friends.#.age [44,68,47]
Queries
You can also query an array for the first match by using #(...), or find all matches with #(...)#.
Queries support the ==, !=, <, <=, >, >= comparison operators,
and the simple pattern matching % (like) and !% (not like) operators.
friends.#(last=="Murphy").first "Dale"
friends.#(last=="Murphy")#.first ["Dale","Jane"]
friends.#(age>45)#.last ["Craig","Murphy"]
friends.#(first%"D*").last "Murphy"
friends.#(first!%"D*").last "Craig"
To query for a non-object value in an array, you can forgo the string to the right of the operator.
children.#(!%"*a*") "Alex"
children.#(%"*a*")# ["Sara","Jack"]
Nested queries are allowed.
friends.#(nets.#(=="fb"))#.first >> ["Dale","Roger"]
Please note that prior to v1.3.0, queries used the #[...] brackets. This was
changed in v1.3.0 as to avoid confusion with the new multipath
syntax. For backwards compatibility, #[...] will continue to work until the
next major release.
The ~ (tilde) operator will convert a value to a boolean before comparison.
Supported tilde comparison type are:
~true Converts true-ish values to true
~false Converts false-ish and non-existent values to true
~null Converts null and non-existent values to true
~* Converts any existing value to true
For example, using the following JSON:
{
"vals": [
{ "a": 1, "b": "data" },
{ "a": 2, "b": true },
{ "a": 3, "b": false },
{ "a": 4, "b": "0" },
{ "a": 5, "b": 0 },
{ "a": 6, "b": "1" },
{ "a": 7, "b": 1 },
{ "a": 8, "b": "true" },
{ "a": 9, "b": false },
{ "a": 10, "b": null },
{ "a": 11 }
]
}
To query for all true-ish or false-ish values:
vals.#(b==~true)#.a >> [2,6,7,8]
vals.#(b==~false)#.a >> [3,4,5,9,10,11]
The last value which was non-existent is treated as false
To query for null and explicit value existence:
vals.#(b==~null)#.a >> [10,11]
vals.#(b==~*)#.a >> [1,2,3,4,5,6,7,8,9,10]
vals.#(b!=~*)#.a >> [11]
Dot vs Pipe
The . is standard separator, but it's also possible to use a |.
In most cases they both end up returning the same results.
The cases where| differs from . is when it's used after the # for Arrays and Queries.
Here are some examples
friends.0.first "Dale"
friends|0.first "Dale"
friends.0|first "Dale"
friends|0|first "Dale"
friends|# 3
friends.# 3
friends.#(last="Murphy")# [{"first": "Dale", "last": "Murphy", "age": 44},{"first": "Jane", "last": "Murphy", "age": 47}]
friends.#(last="Murphy")#.first ["Dale","Jane"]
friends.#(last="Murphy")#|first <non-existent>
friends.#(last="Murphy")#.0 []
friends.#(last="Murphy")#|0 {"first": "Dale", "last": "Murphy", "age": 44}
friends.#(last="Murphy")#.# []
friends.#(last="Murphy")#|# 2
Let's break down a few of these.
The path friends.#(last="Murphy")# all by itself results in
[{"first": "Dale", "last": "Murphy", "age": 44},{"first": "Jane", "last": "Murphy", "age": 47}]
The .first suffix will process the first path on each array element before returning the results. Which becomes
["Dale","Jane"]
But the |first suffix actually processes the first path after the previous result.
Since the previous result is an array, not an object, it's not possible to process
because first does not exist.
Yet, |0 suffix returns
{"first": "Dale", "last": "Murphy", "age": 44}
Because 0 is the first index of the previous result.
Modifiers
A modifier is a path component that performs custom processing on the JSON.
For example, using the built-in @reverse modifier on the above JSON payload will reverse the children array:
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 JSON.@pretty: Make the JSON 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.@dig: Search for a value without providing its entire path. See e8e87f2.
Modifier arguments
A modifier may accept an optional argument. The argument can be a valid JSON payload 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.
{
"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 for more information.
Custom modifiers
You can also add custom modifiers.
For example, here we create a modifier which makes the entire JSON payload upper or lower case.
gjson.AddModifier("case", func(json, arg string) string {
if arg == "upper" {
return strings.ToUpper(json)
}
if arg == "lower" {
return strings.ToLower(json)
}
return json
})
"children.@case:upper" ["SARA","ALEX","JACK"]
"children.@case:lower.@reverse" ["jack","alex","sara"]
Note: Custom modifiers are not yet available in the Rust version
Multipaths
Starting with v1.3.0, GJSON added the ability to join multiple paths together
to form new documents. Wrapping comma-separated paths between [...] or
{...} will result in a new array or object, respectively.
For example, using the given multipath:
{name.first,age,"the_murphys":friends.#(last="Murphy")#.first}
Here we selected the first name, age, and the first name for friends with the last name "Murphy".
You'll notice that an optional key can be provided, in this case "themurphys", to force assign a key to a value. Otherwise, the name of the actual field will be used, in this case "first". If a name cannot be determined, then "" is used.
This results in
{"first":"Tom","age":37,"the_murphys":["Dale","Jane"]}
Literals
Starting with v1.12.0, GJSON added support of json literals, which provides a way for constructing static blocks of json. This is can be particularly useful when constructing a new json document using multipaths.
A json literal begins with the '!' declaration character.
For example, using the given multipath:
{name.first,age,"company":!"Happysoft","employed":!true}
Here we selected the first name and age. Then add two new fields, "company" and "employed".
This results in
{"first":"Tom","age":37,"company":"Happysoft","employed":true}
See issue #249 for additional context on JSON Literals.