@1533-systems/driveline 中文文档教程

Question

Driveline Javascript SDK

Javascript SDK 的核心是类 DrivelineClient。

DrivelineClient.connect('ws://127.0.0.1:8080', {onConnected:main});

const main = (client) => {

  // list all streams
  // name is null when all streams have been listed
  client.listStreams('*', (name)=> console.log(name));

  // list all keys in the Key-Value store
  // name is null when all keys have been listed
  client.listKeys('*', (name) => console.log(name));

  // load a key from the key-value store
  client.load('kv[1]').then(({recordId, record, error}) => {
    if (error) {
        alert('something bad happened: ' + error);
        return;
    }
    // go on with recordId and record
    console.log('loaded record with id:', recordId, 'value:', record);
  });

  // remove all records in the key-value store which keys matching 'kv[...]'
  // this will watch kv[1], kv[12321312], kv[say whaaaat?]
  client.removeMatches('kv[*]');

  // store an object in the key-value store at key 'kv[2]'
  client.store('kv[2]', {message:'hello, world!'});

  // run a live query against a stream.
  // in this case we want every records
  client.continuousQuery('SELECT * FROM STREAM stream1', ({ recordId, record, error}) => {
      // process ... 
  });

};

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 支持标准的 SQL 查询语法，不包括 Joins 和 聚合体。 这意味着 DQL 可用于所有形式的数据过滤 以及实时流上的数据分区。

KV query

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

多键查询是一个 DQL 扩展，可让您订阅多个 事件流，在新流形成时自动订阅， 基于流名称表达式。 流名称表达式使用文件系统/Python Glob, 以?、*和**作为通配匹配字符。

ECMAScript Object Notation (JavaScript extensions)

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

使用以下形式的输入：

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

结果：

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

Operators

下表按以下顺序总结了所有语言运算符 优先权

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}