迭代如何等待Node.js中的sqlite3查询？

Question

I have something like this:

async.forEach(JSONfile,function(item,next){                      
  insertData(item.guid,item.size,item.price,item.latitude,item.longitude,item.property_type,function(){                    
    next();
   });
//code after the insert into db

});

And the function :

function insertData(guid,price,size,longitude,latitude,property_type,callback){
 db.serialize(function() {
  var stmt = db.prepare("INSERT INTO casas VALUES (?,?,?,?,?,?)");
  stmt.run(guid,price,size,longitude,latitude,property_type);
 },function(){
    callback();
 });
}

The issue is that async.forEach always iterates over the JSON and each iteration doesn't wait for the database to finish that query. The point is to get one insert by iteration, and what I'm getting is a lot of queries stacked at the end of the execution. Any help will be appreciated. Thank you

Answer 1

Count the number of operations and when there's nothing left to do , invoke the next callback.

// Get a count of the number of objects
var remaining = require(JSONfile).length;

async.forEach(JSONfile, function(item, next) {
    insertData(
            item.guid,
            item.size,
            item.price,
            item.latitude,
            item.longitude,
            item.property_type, function () {
                // only invoke callback if it's the last time in the loop
                if (!--remaining) next()
            });
    //code after the insert into db
});

This is a common pattern in node.js for handling asynchronous loops. Each time you think it's time to call next, just decrement the remaining number of items. It will will reach zero asynchronously and the very last insertion to complete (regardless of the order they were called) will invoke the callback.