JSON (JavaScript Object Notation) is a lightweight data-interchange format.
JSON (JavaScript Object Notation) is a lightweight data-interchange format.
It is easy for humans to read and write. It is easy for machines to parse
and generate. JSON is a text format that is completely language independent
but uses conventions that are familiar to programmers of the C-family of
languages,
JSON has only types of string, number, boolean, object, array, and null.
This library includes additional types such as date, int, long, double,
counter, binary, UUID, ObjectId (as in BSON), etc.
It is very easy to parse a JSON object:
val doc =
json"""
{
"store": {
"book": [
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
}
}
"""
The interpolator json parse a string to JsObject. To parse an array, use
the interpolator jsan to JsArray. It is also okay to embed
variable references directly in processed string literals.
val x = 1
json"""
{
"x": $x
}
"""
If the string is not a JSON object but any other valid JSON expression,
one may use parseJson method to convert the string to a JsValue.
"1".parseJson
The json interpolator can only be applied to string literals.
If you want to parse a string variable, the parseJson method can
always be employed. If you know the string contains a JSON object,
you may also use the method parseJsObject.
val s = """{"x":1}"""
s.parseJsObject
To serialize a JSON value (of type JsValue) in compact mode, you can
just use toString. To pretty print, use the method prettyPrint.
doc.toString
doc.prettyPrint
With a JsObject or JsArray, you can refer to the individual
elements with a variation of array syntax, like this:
Note that we follow Scala's array access convention by () rather than
[] in JavaScript.
Besides, you can use the dot notation to access its fields/elements
just like in JavaScript:
doc.store.bicycle.color
doc.store.book(0).author
It is worth noting that we didn't define the type/schema of the document
while Scala is a strong type language. In other words, we have both the
type safe features of strong type language and the flexibility of dynamic
language in this JSON library.
If you try to access a non-exist field, JsUndefined is returned.
Although there are already several nice JSON libraries for Scala,
the JSON objects are immutable by design, which is a natural choice
for a functional language. For database, however, data mutation is necessary.
Therefore, JsObject and JsArray are mutable data structures. You can
set/add a field just like in JavaScript:
json.store.bicycle.color = "green"
To delete a field from JsObject, use remove method:
doc.store.book(0) remove "price"
It is same as setting it JsUndefined:
doc.store.book(0).price = `JsUndefined`
To delete an element from JsArray, the remove method will effectively
remove it from the array. However, setting an element to undefined
doesn't reduce the array size.
// delete the first element and array size is smaller
doc.store.book.remove(0)
// set the first element to undefined but array size keeps same
doc.store.book(0) = JsUndefined
It is also possible to append an element or another array to JsArray:
val a = JsArray(1, 2, 3, 4)
a += 5
a ++= JsArray(5, 6)
Common iterative operations such as foreach, map, reduce can be applied
to JsArray too.
doc.store.book.asInstanceOf[JsArray].foreach { book =>
println(book.price)
}
Because Scala is a static language, it is impossible to know
doc.store.book is an array at compile time. So it is typed as
generic JsValue, which is the parent type of specific JSON data types.
Therefore, we use asInstanceOf[JsArray] to convert it to JsArray
in order to use foreach.
JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages,
JSON has only types of string, number, boolean, object, array, and null. This library includes additional types such as date, int, long, double, counter, binary, UUID, ObjectId (as in BSON), etc.
It is very easy to parse a JSON object:
The interpolator
json
parse a string toJsObject
. To parse an array, use the interpolatorjsan
toJsArray
. It is also okay to embed variable references directly in processed string literals.If the string is not a JSON object but any other valid JSON expression, one may use parseJson method to convert the string to a
JsValue
."1".parseJson
The json interpolator can only be applied to string literals. If you want to parse a string variable, the
parseJson
method can always be employed. If you know the string contains a JSON object, you may also use the methodparseJsObject
.To serialize a JSON value (of type JsValue) in compact mode, you can just use
toString
. To pretty print, use the methodprettyPrint
.With a
JsObject
orJsArray
, you can refer to the individual elements with a variation of array syntax, like this:Note that we follow Scala's array access convention by
()
rather than[]
in JavaScript.Besides, you can use the dot notation to access its fields/elements just like in JavaScript:
doc.store.bicycle.color doc.store.book(0).author
It is worth noting that we didn't define the type/schema of the document while Scala is a strong type language. In other words, we have both the type safe features of strong type language and the flexibility of dynamic language in this JSON library.
If you try to access a non-exist field,
JsUndefined
is returned.Although there are already several nice JSON libraries for Scala, the JSON objects are immutable by design, which is a natural choice for a functional language. For database, however, data mutation is necessary. Therefore,
JsObject
andJsArray
are mutable data structures. You can set/add a field just like in JavaScript:json.store.bicycle.color = "green"
To delete a field from
JsObject
, use remove method:It is same as setting it
JsUndefined
:doc.store.book(0).price = `JsUndefined`
To delete an element from
JsArray
, the remove method will effectively remove it from the array. However, setting an element to undefined doesn't reduce the array size.It is also possible to append an element or another array to
JsArray
:Common iterative operations such as
foreach
,map
,reduce
can be applied toJsArray
too.doc.store.book.asInstanceOf[JsArray].foreach { book => println(book.price) }
Because Scala is a static language, it is impossible to know
doc.store.book
is an array at compile time. So it is typed as genericJsValue
, which is the parent type of specific JSON data types. Therefore, we useasInstanceOf[JsArray]
to convert it toJsArray
in order to useforeach
.