driveline

Driveline Python SDK

At the core of the Python SDK is the class DrivelineClient.

import asyncio

from driveline import DrivelineClient, run_async

async def main():
    async with DrivelineClient('ws://127.0.0.1:8080') as client:

        # list all streams
        async for stream_name in await client.list_streams('*'):
            print('found stream:', stream_name)

        # list all keys is the document store
        async for key_name in await client.list_keys('*'):
            print('found document with key', key_name)


        # store a document in the document store
        await client.store('key/1', dict(title='Welcome', body='Hello, world!'))

        # load a key from the document store
        future_record = await client.load('key/1')
        record = await future_record
        print('document associated with key/1 is:', record.record, 'id:', record.record_id)

        # remove all records in the document store with keys matching 'key/...'
        await client.removeMatches('key/*')

        # run a live query against a stream. 
        # We want all records that have an odd index
        def query_handler(res):
            print('query returned record:', res.record, 'id:', res.record_id)
        query = await client.continuous_query('SELECT * FROM STREAM my_stream where index % 1 == 1', query_handler)


        # stop the query
        await asyncio.sleep(10)
        await client.cancel(query)

        # quit
        await client.close()

if __name__ == '__main__':
    run_async(main())

DQL Driveline Query Language

Query syntax

Basic syntax

SELECT <selector> FROM STREAM <stream> [WHERE <expression>]
SELECT * FROM STREAM stream_1
SELECT * FROM STREAM stream_1 WHERE key=value
SELECT time AS t,(2+3) AS five FROM STREAM stream_1 WHERE age BETWEEN 21 AND 25 OR name LIKE 'Joe%'

DQL supports standard SQL query syntax, excluding Joins and Aggregates. This means DQL can be used for all forms of data filtering and partitioning of data over live streams.

KV query

SELECT <selector> FROM <string-key-name-expression> [WHERE <expression>]
SELECT * FROM 'users/*' WHERE color='red'

Multi key query is a DQL extension that lets you subscribe to multiple event streams, automatically subscribing to new streams as they form, based on the stream name expression. Stream name expression use file-system/Pythong Glob, with ?, * and ** serving as the wildcard match characters.

ECMAScript Object Notation (JavaScript extensions)

SELECT {time,name:user.name,phone_number:user.phone.mobile.number,original:{...*}} FROM stream

With inputs of the form:

{time:123, user: {name:'joe', phone: {mobile: {number:'1-800-123-4567'}}}}

Results in:

{time:123,name:'joe',phone_number:'1-800-123-4567',original:{time:123,user:phone:{...}}}

Operators

The following table summarizes all language operators in order of precedence

Name	Description	Example	Additional details
OR	extended logical OR	SELECT * FROM STREAM stream WHERE a OR b	if (a) return a; else return b;
AND	logical AND	SELECT * FROM STREAM stream WHERE a AND b	if (a && b) return true; else return false;
NOT	logical NOT	SELECT * FROM STREAM stream WHERE NOT a	if (a) return false; else return true;
IS [NOT] NULL	Null check	SELECT * FROM STREAM stream WHERE a IS NOT NULL	if (null===a) return true; return false;
IN	Set lookup	SELECT * FROM STREAM stream WHERE a IN (1,2,3)	All values in paranthesis must be constants
BETWEEN	Compare range	SELECT * FROM STREAM stream WHERE a BETWEEN b AND c	if (b<c) return (a>=b && a<=c); else return (a>=c && a<=b);
= >= <= != > < !< !> <>	Compare	SELECT * FROM STREAM STREAM WHERE a <> b
LIKE	Pattern match	SELECT * FROM STREAM stream WHERE a like '%b%'	_ stands for single, % stands for multi-char match
+ -	Unary plus/minus	SELECT * FROM STREAM stream WHERE -5 < +5
+ -	Addition	SELECT * FROM STREAM stream WHERE 1+2=3
* / %	Multiplicative	SELECT * FROM STREAM stream WHERE 3%2=1
( exp )	Paranthesis	SELECT * FROM STREAM stream WHERE (1+2)*3=9
true false null	Constant	SELECT * FROM STREAM stream WHERE true != false
-123.45e-1	Numeric constant
'hello'	String constant		SELECT * FROM stream WHERE name='joe'
name	Identifier	SELECT name FROM STREAM stream
`user name`	Identifier	SELECT `user name` FROM STREAM stream	(backticks) Allows using identifier names that are otherwise invalid, e.g., contain invalid characters or symbols

Built-in functions

Name	Description	Example
ABS	Absolute value float=>float	SELECT ABS(-5) AS num FROM stream {num:5}
CEIL	Rounded up value float=>float	SELECT CEIL(4.5) AS num FROM stream {num:5}
FLOOR	Rounded down value float=>float	SELECT FLOOR(4.5) AS num FROM stream {num:4}
EXP	Natural exponent float=>float	SELECT EXP(1) AS num FROM stream {num:2.718281828459045}
LN	Natural logarithm float=>float	SELECT LN(2) AS num FROM stream {num:0.6931471805599453}
SQRT	Square root float=>float	SELECT SQRT(9) AS num FROM stream {num:3}
HASH	Hash function any=>uint64	SELECT HASH('abc') AS num FROM stream {num:4952883123889572249}
CHAR_LENGTH	Length of string string->int32	SELECT CHAR_LENGTH('abc') AS num FROM stream {num:3}
POSITION	Index of substring in string string,string->int32	SELECT POSITION('bc' IN 'abc') AS num FROM stream {num:2}
LOCATE	Index of substring in string string,string->int32	SELECT LOCATE('bc', 'abc') AS num FROM stream {num:2}