set a json value quickly

SJSON is a Go package that provides a very fast and simple way to set a value in a json document. The purpose for this library is to provide efficient json updating for the SummitDB project. For quickly retrieving json values check out GJSON.

For a command line interface check out JSONed.

Getting Started

Installing

To start using SJSON, install Go and run go get:

$ go get -u github.com/tidwall/sjson

This will retrieve the library.

Set a value

Set sets the value for the specified path. A path is in dot syntax, such as "name.last" or "age". This function expects that the json is well-formed and validated. Invalid json will not panic, but it may return back unexpected results. Invalid paths may return an error.

package main
import"github.com/tidwall/sjson"constjson=`{"name":{"first":"Janet","last":"Prichard"},"age":47}`funcmain() {
value, _:=sjson.Set(json, "name.last", "Anderson")
println(value)
}

This will print:

{"name":{"first":"Janet","last":"Anderson"},"age":47}

Path syntax

A path is a series of keys separated by a dot. The dot and colon characters can be escaped with ''.

{
"name": {"first": "Tom", "last": "Anderson"},
"age":37,
"children": ["Sara","Alex","Jack"],
"fav.movie": "Deer Hunter",
"friends": [
{"first": "James", "last": "Murphy"},
{"first": "Roger", "last": "Craig"}
]
}

"name.last" >> "Anderson"
"age" >> 37
"children.1" >> "Alex"
"friends.1.last" >> "Craig"

The -1 key can be used to append a value to an existing array:

"children.-1" >> appends a new value to the end of the children array

Normally number keys are used to modify arrays, but it's possible to force a numeric object key by using the colon character:

{
"users":{
"2313":{"name":"Sara"},
"7839":{"name":"Andy"}
}
}

A colon path would look like:

"users.:2313.name" >> "Sara"

Supported types

Pretty much any type is supported:

sjson.Set(`{"key":true}`, "key", nil)
sjson.Set(`{"key":true}`, "key", false)
sjson.Set(`{"key":true}`, "key", 1)
sjson.Set(`{"key":true}`, "key", 10.5)
sjson.Set(`{"key":true}`, "key", "hello")
sjson.Set(`{"key":true}`, "key", map[string]interface{}{"hello":"world"})

When a type is not recognized, SJSON will fallback to the encoding/json Marshaller.

Examples

Set a value from empty document:

value, _:=sjson.Set("", "name", "Tom")
println(value)
// Output:// {"name":"Tom"}

Set a nested value from empty document:

value, _:=sjson.Set("", "name.last", "Anderson")
println(value)
// Output:// {"name":{"last":"Anderson"}}

Set a new value:

value, _:=sjson.Set(`{"name":{"last":"Anderson"}}`, "name.first", "Sara")
println(value)
// Output:// {"name":{"first":"Sara","last":"Anderson"}}

Update an existing value:

value, _:=sjson.Set(`{"name":{"last":"Anderson"}}`, "name.last", "Smith")
println(value)
// Output:// {"name":{"last":"Smith"}}

Set a new array value:

value, _:=sjson.Set(`{"friends":["Andy","Carol"]}`, "friends.2", "Sara")
println(value)
// Output:// {"friends":["Andy","Carol","Sara"]

Append an array value by using the -1 key in a path:

value, _:=sjson.Set(`{"friends":["Andy","Carol"]}`, "friends.-1", "Sara")
println(value)
// Output:// {"friends":["Andy","Carol","Sara"]

Append an array value that is past the end:

value, _:=sjson.Set(`{"friends":["Andy","Carol"]}`, "friends.4", "Sara")
println(value)
// Output:// {"friends":["Andy","Carol",null,null,"Sara"]

Delete a value:

value, _:=sjson.Delete(`{"name":{"first":"Sara","last":"Anderson"}}`, "name.first")
println(value)
// Output:// {"name":{"last":"Anderson"}}

Delete an array value:

value, _:=sjson.Delete(`{"friends":["Andy","Carol"]}`, "friends.1")
println(value)
// Output:// {"friends":["Andy"]}

Delete the last array value:

value, _:=sjson.Delete(`{"friends":["Andy","Carol"]}`, "friends.-1")
println(value)
// Output:// {"friends":["Andy"]}

Performance

Benchmarks of SJSON alongside encoding/json, ffjson, EasyJSON, and Gabs

Benchmark_SJSON-8 3000000 805 ns/op 1077 B/op 3 allocs/op
Benchmark_SJSON_ReplaceInPlace-8 3000000 449 ns/op 0 B/op 0 allocs/op
Benchmark_JSON_Map-8 300000 21236 ns/op 6392 B/op 150 allocs/op
Benchmark_JSON_Struct-8 300000 14691 ns/op 1789 B/op 24 allocs/op
Benchmark_Gabs-8 300000 21311 ns/op 6752 B/op 150 allocs/op
Benchmark_FFJSON-8 300000 17673 ns/op 3589 B/op 47 allocs/op
Benchmark_EasyJSON-8 1500000 3119 ns/op 1061 B/op 13 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 though one of the following search paths:

widget.window.name
widget.image.hOffset
widget.text.onMouseUp

These benchmarks were run on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.7.

Contact

Josh Baker @tidwall

License

SJSON source code is available under the MIT License.