From f73dd9bfd85265ba8013eb3e64d7216b76b74801 Mon Sep 17 00:00:00 2001 From: Josh Baker Date: Fri, 28 Jun 2019 17:11:56 -0700 Subject: [PATCH] Create PATH-SYNTAX.md --- PATH-SYNTAX.md | 227 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 227 insertions(+) create mode 100644 PATH-SYNTAX.md diff --git a/PATH-SYNTAX.md b/PATH-SYNTAX.md new file mode 100644 index 0000000..c8e578f --- /dev/null +++ b/PATH-SYNTAX.md @@ -0,0 +1,227 @@ +# 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 +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"] +``` +