node-sqlite3 with iojs, koa and yield - node.js

Question

I'm new to iojs and am trying to write a small web application with koa and node-sqlite3.
One thing I couldn't quite get my head around is how to use the 'yield' syntax on the node-sqlite3 callback based API.
I've googled around and all I've found was this stackoverflow post (synchronous sqlite transactions node), which says this is possible.
Can anyone please give me a pointer to more concrete examples?
Thanks in advance

Answer 1

After some more digging, I found some hint from the stackoverflow post Koa.js request with promises is hanging.
The trick is to use the native Promises.
Sample code below works with iojs v1.6.4 and Koa 0.19.0
var koa = require('koa');
var app = koa();
var route = require('koa-route');
var sqlite3 = require('sqlite3').verbose();
var db = new sqlite3.Database(':memory:');
function *query() {
var promise = new Promise(function(resolve, reject) {
var result = [];
db.serialize(function() {
db.run("DROP TABLE IF EXISTS lorem");
db.run("CREATE TABLE lorem (info TEXT)");
var stmt = db.prepare("INSERT INTO lorem VALUES (?)");
for (var i = 0; i < 10; i++) {
stmt.run("Ipsum " + i);
}
stmt.finalize();
db.all("SELECT rowid AS id, info FROM lorem", function(err, rows) {
resolve(rows);
});
});
});
return promise;
}
function *handler() {
this.body = yield query();
this.status = 200;
}
app.use(route.get('/list', handler));
app.listen(3000);

Answer 2

there is a nodejs module called co-sqlite3 here :
https://www.npmjs.com/package/co-sqlite3
promise based node-sqlite3 named co-sqlite3 for co or koa
Installing
npm install co-sqlite3
Usage
work with co
var co = require('co');
var sqlite3 = require('co-sqlite3');
co(function*() {
//connect a database
var db = yield sqlite3('test.db');
// create a table
yield db.run('CREATE TABLE IF NOT EXISTS testtable (id INT NOT NULL)');
var stmt = yield db.prepare('INSERT INTO testtable(id) VALUES( ? )');
for(var i =0 ; i < 100 ; i++){
yield stmt.run(i);
}
stmt.finalize();
var row = yield db.get('SELECT * FROM testtable WHERE id < ? ORDER BY ID DESC ' ,[50]);
console.log(row); // {id: 49}
var rows = yield db.all('SELECT * FROM testtable');
console.log(rows.length);
}).catch(function(err) {
console.log(err.stack);
});
work with koa
var koa = require('koa');
var sqlite3 = require('co-sqlite3');
var app = koa();
app.use(function*(next){
this.db = yield sqlite3('test.db');
yield next ;
});
app.use(function* (){
this.body = yield this.db.get('SELECT * FROM testtable WHERE id < ? ORDER BY ID DESC ' ,[50]);
})
app.listen(3000);
just as a promise
var sqlite3 = require('co-sqlite3');
sqlite3('test.db').then(function(db){
db.get('SELECT * FROM testtable WHERE id < ? ORDER BY ID DESC ' ,[50])
.then(function(row){
console.log(row);
});
});

Answer 3

While promises work, the major advantage of using koa is to leverage generators (the yield keyword). For that to happen, the library you're using needs to be prepared to work with generators.
I know you've specified you're using sqlite, but for an example of database access with yield, see how this mongodb package co-monk works:
yield users.insert({ name: 'Tobi', species: 'ferret' });
var res = yield users.findOne({ name: 'Tobi' });
res.name.should.equal('Tobi');
While you could use the co package for wrapping node-sqlite3 yourself, if you're starting you'll probably find it easier to use one of those existing co-based libraries.
There seems to be a generator-ready package for MySQL too, though I couldn't find any equivalent for sqlite.
In case that helps, here's a more complete blog post with examples of using co-monk: http://www.marcusoft.net/2014/04/koaExamples.html