Question

I’m trying to render a page of ‘projects’ retrieved from a database. There are two types of projects concerning the user, the projects which they own, and the projects which they are a member of.

I’m using two asynchronous database queries, however they could finish at different times and I only want to render the page upon them both completing.

Question:
How can I delay the rendering until the database transactions are complete?

  var username = req.session.username;
  var memberProjects = [];
  var ownerProjects = [];
  var membersQuery = false;
  var ownerQuery = false;

  projects.find({"members.username" : username}).toArray(function(err, results)
  {
    for(var i = 0; i < results.length; i++)
    {
      var project = {
        title : results[i].title,
        id : results[i]._id
      }
      memberProjects[i] = project;
    }
    membersQuery = true;
  });

  projects.find({owner : req.session.username}).toArray(function(err, results)
  {
    for(var i = 0; i < results.length; i++)
    {
      var project = {
        title : results[i].title,
        id : results[i]._id
      }
      ownerProjects[i] = project;
    }
    ownerQuery = true;
  });

  if( membersQuery && ownerQuery )
  {        
    res.render('project', {
      ownerProjects : ownerProjects,
      memberProjects : memberProjects
    });        
  }

Answer 1

I’ve got a working answer, i’m not sure whether it’s correct or not. Please correct me if there is a better approach. I’m calling a function at the end of each database transaction:

  var username = req.session.username;
  var memberProjects = [];
  var ownerProjects = [];
  var membersQuery = false;
  var ownerQuery = false;

  projects.find({"members.username" : username}).toArray(function(err, results)
  {
    for(var i = 0; i < results.length; i++)
    {
      var project = {
        title : results[i].title,
        id : results[i]._id
      }
      memberProjects[i] = project;
    }
    membersQuery = true;
    render();
  });

  projects.find({owner : req.session.username}).toArray(function(err, results)
  {
    for(var i = 0; i < results.length; i++)
    {
      var project = {
        title : results[i].title,
        id : results[i]._id
      }
      ownerProjects[i] = project;
    }
    ownerQuery = true;
    render();
  });

  function render(){
    if( membersQuery && ownerQuery )
    {        
      res.render('project', {
        ownerProjects : ownerProjects,
        memberProjects : memberProjects
      });        
    }
  }