Lifting-json-manipulation - adding to the right place

Question

consider the following json:

{ "type":"A1", "system":{ "path":"/example.org/FooBar", "lastModified":"2013-10-01T12:00:00Z" }, "fields":{ "foo1":["bar1"], "foo2":["bar2"], "foo3":["bar3"] } } 

now using lift-json i want to change this json to:

 { "type":"A1", "system":{ "path":"/example.org/FooBar", "lastModified":"2013-10-01T12:00:00Z" }, "fields":{ "foo1":["bar1"], "foo2":["bar2"], "foo3":["bar3"] }, "injected":{ "bar1":"foo1", "bar2":"foo2" } } 

So, I tried the following:

 scala> val json = parse(""" |{ | "type":"A1", | "system":{ | "path":"/example.org/FooBar", | "lastModified":"2013-10-01T12:00:00Z" | }, | "fields":{ | "foo1":["bar1"], | "foo2":["bar2"], | "foo3":["bar3"] | } |}""") json: net.liftweb.json.JValue = JObject(List(JField(type,JString(A1)), JField(system,JObject(List(JField(path,JString(/example.org/FooBar)), JField(lastModified,JString(2013-10-01T12:00:00Z))))), JField(fields,JObject(List(JField(foo1,JArray(List(JString(bar1)))), JField(foo2,JArray(List(JString(bar2)))), JField(foo3,JArray(List(JString(bar3))))))))) scala> json transform{case JObject(l) => JObject(l ::: List(JField("injected", ("bar1" -> "foo1") ~ ("bar2" -> "foo2"))))} res0: net.liftweb.json.JsonAST.JValue = JObject(List(JField(type,JString(A1)), JField(system,JObject(List(JField(path,JString(/example.org/FooBar)), JField(lastModified,JString(2013-10-01T12:00:00Z)), JField(injected,JObject(List(JField(bar1,JString(foo1)), JField(bar2,JString(foo2)))))))), JField(fields,JObject(List(JField(foo1,JArray(List(JString(bar1)))), JField(foo2,JArray(List(JString(bar2)))), JField(foo3,JArray(List(JString(bar3)))), JField(injected,JObject(List(JField(bar1,JString(foo1)), JField(bar2,JString(foo2)))))))), JField(injected,JObject(List(JField(bar1,JString(foo1)), JField(bar2,JString(foo2))))))) scala> Printer.pretty(render(res0)) res1: String = { "type":"A1", "system":{ "path":"/example.org/FooBar", "lastModified":"2013-10-01T12:00:00Z", "injected":{ "bar1":"foo1", "bar2":"foo2" } }, "fields":{ "foo1":["bar1"], "foo2":["bar2"], "foo3":["bar3"], "injected":{ "bar1":"foo1", "bar2":"foo2" } }, "injected":{ "bar1":"foo1", "bar2":"foo2" } } 

and, as you can see, the injected part injected been added to fields and system . I just wanted to add it once under the root.

So what am I doing wrong? and how can I convert json to the structure I need?

Answer 1

The problem you are facing is that the partial function defined in the conversion maps at all possible levels within the json structure. Since the “system” and “field” components of the external JObject themselves are JObjects, they correspond to a partial function and are also translated.

To get the result you are looking for, you will need to make the match more specific, for example:

 json transform {case JObject(fields) if (fields contains JField("type", "A1")) => JObject(l ::: ... 

using some unique information about the outermost object (here it has a "type" set to "A1").

Alternatively, the json elevator has a merge option, which I could not handle, but which can give what you want:

 json merge JObject(JField("injected", ...) :: Nil) 

Answer 2

If you only need to add the field in one place, transform is not the best tool, you can just use ~ instead:

 val newJson = json match { case obj: JObject => obj ~ ("injected" -> ("bar1" -> "foo1") ~ ("bar2" -> "foo2")) case _ => throw new RuntimeException("Did not receive a JSON object!") } 

If you know that you will always parse the object, you can drop json in JObject and avoid the proper work here.