Project: HwameiStor (Runtime / Cloud Native Storage)
File: SYNTAX.md

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 . Use the to experiment with the syntax online. 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 `?`. 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, "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. 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" ``` 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" ``` Special purpose characters, such as `.`, `*`, and `?` can be escaped with `\`. ```go 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 // Go val := gjson.Get(json, "fav\\.movie") // must escape the slash val := gjson.Get(json, `fav\.movie`) // no need to escape the slash ``` ```rust // 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 ``` 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] ``` 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"] ``` 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 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: ```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` 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 and . 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. 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 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

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 . 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 for more information.* 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"] ``` Note: Custom modifiers are not yet available in the Rust version 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 ```json {"first":"Tom","age":37,"the_murphys":["Dale","Jane"]} ``` 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 . 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 ```json {"first":"Tom","age":37,"company":"Happysoft","employed":true} ``` See issue for additional context on JSON Literals.