promise

Promise notation

We strongly recommend using the promise notation for all async interactions with AlaSQL. This includes every time 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 command in the same string they will (until it is fixed) run sync within the async call to alasql - so a command like "INSERT ...; SELECT * ..." the second command might start before the first command is done. This is not a problem unless you are using a DB that demands async interaction (like indexedDB).

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 concept of

This means you can chain .then(...) methods when 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);
        })