promise

Promise notation

We strongly recommend using the promise notation for all async interaction with AlaSQL:

alasql.promise(sql [, params])
      .then(function(data){
           console.log(data);
      }).catch(function(err){
           console.log('Error:', err);
      });

Example:

alasql.promise('SELECT * FROM XLS("mydata.xls") GROUP BY name WHERE lastname LIKE "A%" and city = "London"')
      .then(function(res){
           console.log(res);
      }).catch(function(err){
           console.log('error:', err);
      });

AlaSQL uses ES6 promises which are available in most modern browsers. AlaSQL brings a polyfill if Promise is not supported.

Chain of promises

If you put more than one SQL commands in the same string they will (until its fixed) run sync within in the async call to alasql - so a command like "INSERT ...; SELECT * ..." might not give the expected result as the select might run before the insert is done.

From version 0.2.5 you are able to pass an array of queries to alasql.promise and they will execute in a chain (so one after the return of the promise of the other). For the moment the only drawback is that you only get the result from the last query in the chain.

alasql.promise([
	'CREATE FILESTORAGE DATABASE test123("./testDBfile.json")', 
	'ATTACH FILESTORAGE DATABASE test123("./testDBfile.json")', 
	'USE test123', 
	'CREATE TABLE IF NOT EXISTS products (id INT, category_id INT, name string, created_at DATE)', 
	['INSERT INTO products (id, category_id, name, created_at) VALUES (?,?,?,?)', [1, 2, 'XYZ', new Date()] ],
	'SELECT * FROM products'	
]).then(function(res){
	console.log('Result from last query:',res)
}).catch(function(reason){
	console.log('Error:',reason)
})

Please note that to be able to combine a query with parameters instead of a string one must pass an array with the query string at index 0 and the array of parameters at index 1.

More about proimse

If you are not used to work with promises have a look at http://www.2ality.com/2014/10/es6-promises-api.html where the concepts are explained very well. Central to the usage is the consept of

Stating that if you can chain .then(...)'s if they return another promise. For AlaSQL this means you can return a alasql.promise object from a .then and keep the code unnested.

Example of the notation:

alasql.promise([
                'UPDATE abc values (5)',
                'VALUE OF SELECT max(val)'
        ]).then(function(res){
                console.log('max value found:', res);
                var n = prompt('Please write a number between 0 and '+res);
                return alasql.promise('SELECT * FROM abc WHERE val = '+n)
        }).then(function(res){
                console.log('You got: ', res);
        })