promise

Promise notation

We strongly recommend using the promise notation for all async interaction with AlaSQL. This includes everytime a filename or URL is part of the SQL.

alasql.promise(sql(s) [, params])
      .then(function(data){
           // Display data
      }).catch(function(error){
           // Log the error
      });

The .promise part can be omitted if the SQL is given as an array (format documented in "Chain of promises"). Example of the lazy promise notation:

alasql(['SELECT * FROM XLS("mydata.xls") GROUP BY name WHERE lastname LIKE "A%" and city = "London"'])
      .then(function(data){
           // Display data
      }).catch(function(error){
           // Display error
      });

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.

Pass an array of queries to alasql.promise to execute in a chain (so one after the return of the promise of the other).

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('Results from all queries:',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 promise

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);
        })