How do you modify the contents of a JSON object, and write it back out?

[Henry Minsky]

Hello lift-experts!

I am trying to use the lift json library, and am confused about a very
simple task.

I have some JSON which contains an object, one of whose fields is a
list of strings:


scala> val j = parse("""{ "a": ["123", "1bfc", "ocac"], "b": 17}""")
j: net.liftweb.json.package.JValue =
JObject(List(JField(a,JArray(List(JString(123), JString(1bfc),
JString(ocac)))), JField(b,JInt(17))))

If I 'extract' the "a" field, I can get a List[String]

scala> (j \ "a").extract[List[String]]
res15: List[String] = List(123, 1bfc, ocac)

My question is, if I add or remove something from the list, how can I
stuff it back into the JSON object? I.e., I want to treat the field
"a" like a key in a Map, and update the value using something like a
Map.updated(key, newvalue) call?

Example code snippets appreciated!

Thanks!

[Joni Freeman]

Hi,

You can't modify a JValue since it is immutable. Transform function can
be used to make transformation on JValues. Example:

j transform {
case JField("a",JArray(xs)) => JField("a",JArray(JString("x")::xs))
}

Removal is done by transforming a value into JNothing:

j transform {
case JField("a", JArray(xs)) => JNothing
}

Two JSON:s can be merged with 'merge' function:

scala> val j1 = ("foo" -> 1) ~ ("bar" -> 2)
scala> val j2 = ("foo" -> 1) ~ ("baz" -> 3)
scala> j1 merge j2
res6: net.liftweb.json.package.JValue =
JObject(List(JField(foo,JInt(1)), JField(bar,JInt(2)),
JField(baz,JInt(3))))

Those are perhaps the most common ways to make transformations on the
JSON. 'replace' and 'remove' are helpers which can be used too.

Cheers Joni

[Henry Minsky]

Thanks, that's very helpful!

Can you tell me where to find the documentation on the json library, I cannot seem to locate
it on Google?

The only doc pointer I found was broken, on this page

http://www.scala-lang.org/node/4225

which points to

Currently the docs live here:
http://github.com/dpp/liftweb/tree/master/lift-base/lift-json/

Thanks!

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[Tim Nelson]

https://github.com/lift/framework/tree/master/core/json

[Antonio Salazar Cardozo]

Prepare to have your mind blown by the awesomeness detailed in the docs ;)

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