gjson/SYNTAX.md

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2019-06-29 03:11:56 +03:00
# 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](#path-structure)
- [Basic](#basic)
- [Wildcards](#wildcards)
- [Escape Character](#escape-character)
- [Arrays](#arrays)
- [Queries](#queries)
- [Dot vs Pipe](#dot-vs-pipe)
- [Modifiers](#modifiers)
The definitive implemenation is [github.com/tidwall/gjson](https://github.com/tidwall/gjson).
## 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
```json
{
"name": {"first": "Tom", "last": "Anderson"},
"age":37,
"children": ["Sara","Alex","Jack"],
"fav.movie": "Deer Hunter",
"friends": [
{"first": "Dale", "last": "Murphy", "age": 44},
{"first": "Roger", "last": "Craig", "age": 68},
{"first": "Jane", "last": "Murphy", "age": 47}
]
}
```
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.
```go
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.
```go
child*.2 "Jack"
c?ildren.0 "Sara"
```
### Escape character
Special purpose characters, such as `.`, `*`, and `?` can be escaped with `\`.
```go
fav\.movie "Deer Hunter"
```
### Arrays
The `#` character allows for digging into JSON Arrays.
To get the length of an array you'll just use the `#` all by itself.
```go
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.
```go
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.
```go
children.#[!%"*a*"] "Alex"
children.#[%"*a*"]# ["Sara","Jack"]
```
### 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](#arrays) and [Queries](#queries).
Here are some examples
```go
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
```json
[{"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
```json
["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
```json
{"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:
```go
children.@reverse ["Jack","Alex","Sara"]
children.@reverse.0 "Jack"
```
There are currently three 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.
#### 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.
```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 which makes the entire JSON payload upper or lower case.
```go
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"]
```