JSON Item Methods
Item methods are postfix operators that operate on a JSON value and return a JSON item. When run against a sequence the method is applied to each item in the sequence.
Multiple item methods can be used. For example: $.agestring.double().floor()
Note: All item methods except for type() and size() unwrap arrays in lax mode.
Type()
• Returns a character string
• Returns “null”, “Boolean”, “number”, “string”, “array”, or “object”
• Does not unwrap arrays. Returns “array” even in lax mode.
Example: LAX $.* ? (@.TYPE() == "number")
Size()
• Returns an integer value
• For an object or scalar, returns 1
• For an array, returns the number of elements of the array
• Does not unwrap arrays even in lax mode
Example: strict $.[1] ? (@.type() == "array" && @.size() > 1)
Numeric methods
• Ceiling(), floor(), abs() have the same functionality as the numeric functions in SQL.
• Double() coerces a string or numeric into a numeric float.
Keyvalue()
• Used to examine an object with unknown schema.
• Returns a sequence of objects with three key-value pairs whose keys are name, value, and id. One object is returned for each key:value pair of the input object.
– Name and value will be the keys and values of the object.
– Id is an integer that is a unique identifier for the input SQL or JSON object.
Assume a query runs the keyvalue() method on X objects and each object has Y key:value pairs. X*Y total objects are returned, and every “Y” object will have a unique ID that corresponds to the original object. The id allows reconstructing the original objects from the output of keyvalue().
Note: The ids are only unique within the scope of the query that uses keyvalue(). The same objects can have different id numbers when run in separate queries.
• In lax mode, the input is unwrapped, so keyvalue() on an array of X items returns a sequence of X items.
• Id numbers are only unique for the query in which keyvalue() is called. They can be reused in other queries.
Example: Given the object {who: "Fred", what: 64}, keyvalue() returns:
{name: "who", value: "Fred", id: 9045},
{name: "what", value: 64, id: 9045}
To find the value of all “names”, select Keyvalue().name which returns the sequence("who", "what").
Example: Given the sequence:
[{"Building":"Empire", "Unit":"3F"}, {"row":"A", "Seat":6}]
keyvalue() returns four objects:
{ name: "Building", value: "Empire", id: 1000 },
{ name: "Unit", value: "3F", id: 1000 },
{ name: "row", value: "A", id: 1001 },
{ name: "Seat", value: 6, id: 1001 }
Last modified date: 08/29/2024