JSON Support
Cassandra 2.2 introduces JSON support to SELECT <select-statement> and
INSERT <insert-statement> statements.
This support does not fundamentally alter the CQL API (for example, the schema is still
enforced).
It simply provides a convenient way to work with JSON documents.
SELECT JSON
With SELECT statements, the JSON keyword is used to return each row as a single JSON encoded map.
The remainder of the SELECT statement behavior is the same.
The result map keys match the column names in a normal result set.
For example, a statement like SELECT JSON a, ttl(b) FROM … would result in a map with keys "a" and "ttl(b)".
However, there is one notable exception: for symmetry with INSERT JSON behavior, case-sensitive column names with upper-case letters will be surrounded with double quotes.
For example, SELECT JSON myColumn FROM … would result in a map key "\"myColumn\"" with escaped quotes).
The map values will JSON-encoded representations (as described below) of the result set values.
INSERT JSON
With INSERT statements, the new JSON keyword can be used to enable
inserting a JSON encoded map as a single row. The format of the JSON
map should generally match that returned by a SELECT JSON statement on
the same table. In particular, case-sensitive column names should be
surrounded with double quotes. For example, to insert into a table with
two columns named "myKey" and "value", you would do the following:
INSERT INTO mytable JSON '{ "\"myKey\"": 0, "value": 0}';By default (or if DEFAULT NULL is explicitly used), a column omitted
from the JSON map will be set to NULL, meaning that any pre-existing
value for that column will be removed (resulting in a tombstone being
created). Alternatively, if the DEFAULT UNSET directive is used after
the value, omitted column values will be left unset, meaning that
pre-existing values for those column will be preserved.
JSON Encoding of Cassandra Data Types
Where possible, Cassandra will represent and accept data types in their
native JSON representation. Cassandra will also accept string
representations matching the CQL literal format for all single-field
types. For example, floats, ints, UUIDs, and dates can be represented by
CQL literal strings. However, compound types, such as collections,
tuples, and user-defined types must be represented by native JSON
collections (maps and lists) or a JSON-encoded string representation of
the collection.
The following table describes the encodings that Cassandra will accept
in INSERT JSON values (and fromJson() arguments) as well as the
format Cassandra will use when returning data for SELECT JSON
statements (and fromJson()):
| Type | Formats accepted | Return format | Notes |
|---|---|---|---|
|
string |
string |
Uses JSON’s |
|
integer, string |
integer |
String must be valid 64 bit integer |
|
string |
string |
String should be 0x followed by an even number of hex digits |
|
boolean, string |
boolean |
String must be "true" or "false" |
|
string |
string |
Date in format |
|
integer, float, string |
float |
May exceed 32 or 64-bit IEEE-754 floating point precision in client-side decoder |
|
integer, float, string |
float |
String must be valid integer or float |
|
integer, float, string |
float |
String must be valid integer or float |
|
string |
string |
IPv4 or IPv6 address |
|
integer, string |
integer |
String must be valid 32 bit integer |
|
list, string |
list |
Uses JSON’s native list representation |
|
map, string |
map |
Uses JSON’s native map representation |
|
integer, string |
integer |
String must be valid 16 bit integer |
|
list, string |
list |
Uses JSON’s native list representation |
|
string |
string |
Uses JSON’s |
|
string |
string |
Time of day in format |
|
integer, string |
string |
A timestamp. Strings constant allows to input |
|
string |
string |
Type 1 UUID. See |
|
integer, string |
integer |
String must be valid 8 bit integer |
|
list, string |
list |
Uses JSON’s native list representation |
|
map, string |
map |
Uses JSON’s native map representation with field names as keys |
|
string |
string |
See |
|
string |
string |
Uses JSON’s |
|
integer, string |
integer |
Variable length; may overflow 32 or 64 bit integers in client-side decoder |
The fromJson() Function
The fromJson() function may be used similarly to INSERT JSON, but
for a single column value. It may only be used in the VALUES clause of
an INSERT statement or as one of the column values in an UPDATE,
DELETE, or SELECT statement. For example, it cannot be used in the
selection clause of a SELECT statement.
The toJson() Function
The toJson() function may be used similarly to SELECT JSON, but for
a single column value. It may only be used in the selection clause of a
SELECT statement.
