JSON Support

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
`ascii`	string	string	Uses JSON’s `\u` character escape
`bigint`	integer, string	integer	String must be valid 64 bit integer
`blob`	string	string	String should be 0x followed by an even number of hex digits
`boolean`	boolean, string	boolean	String must be “true” or “false”
`date`	string	string	Date in format `YYYY-MM-DD`, timezone UTC
`decimal`	integer, float, string	float	May exceed 32 or 64-bit IEEE-754 floating point precision in client-side decoder
`double`	integer, float, string	float	String must be valid integer or float
`float`	integer, float, string	float	String must be valid integer or float
`inet`	string	string	IPv4 or IPv6 address
`int`	integer, string	integer	String must be valid 32 bit integer
`list`	list, string	list	Uses JSON’s native list representation
`map`	map, string	map	Uses JSON’s native map representation
`smallint`	integer, string	integer	String must be valid 16 bit integer
`set`	list, string	list	Uses JSON’s native list representation
`text`	string	string	Uses JSON’s `\u` character escape
`time`	string	string	Time of day in format `HH-MM-SS[.fffffffff]`
`timestamp`	integer, string	string	A timestamp. Strings constant allows to input `timestamps as dates <timestamps>`. Datestamps with format `YYYY-MM-DD HH:MM:SS.SSS` are returned.
`timeuuid`	string	string	Type 1 UUID. See `constant` for the UUID format
`tinyint`	integer, string	integer	String must be valid 8 bit integer
`tuple`	list, string	list	Uses JSON’s native list representation
`UDT`	map, string	map	Uses JSON’s native map representation with field names as keys
`uuid`	string	string	See `constant` for the UUID format
`varchar`	string	string	Uses JSON’s `\u` character escape
`varint`	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.