9.0 KiB
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.
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 you 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.
For example, using the following JSON:
{
"vals": [
{ "a": 1, "b": true },
{ "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 }
]
}You can now query for all true(ish) or false(ish) values:
vals.#(b==~true)#.a >> [1,2,6,7,8]
vals.#(b==~false)#.a >> [3,4,5,9,10,11]The last value which was non-existent is treated as
false
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")#|# 2Let’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.
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 “the_murphys”, 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"]}