How to perform initial setup in koa with rethinkdb

问题

Im using rethinkdbdash with koa and trying to figure out how to perform a set up of the database when the app first starts. Im trying to accomplish something similar to Segphalt's cats of instagram tutorial but using koa.

var conn;
r.connect(config.database).then(function(c) {
  conn = c;
  return r.dbCreate(config.database.db).run(conn);
})
.then(function() {
  return r.tableCreate("instacat").run(conn);
})
.then(function() {
  return q.all([
    r.table("instacat").indexCreate("time").run(conn),
    r.table("instacat").indexCreate("place", {geo: true}).run(conn)
  ]);
})
.error(function(err) {
  if (err.msg.indexOf("already exists") == -1)
    console.log(err);
})
.finally(function() {
  r.table("instacat").changes().run(conn)
  .then(function(cursor) {
    cursor.each(function(err, item) {
      if (item && item.new_val)
        io.sockets.emit("cat", item.new_val);
    });
  })
  .error(function(err) {
    console.log("Error:", err);
  });

I've tried to just yield instead of chaining the promises but that throws an error due to invalid syntax.

 try {
   yield r.dbCreate(config.database.db).run();
   yield r.tableCreate('user').run();
 }
 catch (err) {
   if (err.message.indexOf("already exists") == -1)
      console.log(err.message);
 }

app.listen(port);

What is the best way to perform this type of setup including performing a query that runs the .changes() in koa, so that it only executes once the server starts up and not on every request cycle that comes through. Or is there a better way to accomplish this in koa?

回答1:

You can only use the yield keyword inside of a generator function (one with an asterisk in the signature). Typically, if you want to use yield to wait for completion of a promise, you would wrap the entire set of operations with a generator-based coroutine.

There are two libraries that you can use for this:

Co: https://www.npmjs.com/package/co
Bluebird: https://www.npmjs.com/package/bluebird

Co is what Koa uses under the hood in all of its middleware handlers, but I personally prefer Bluebird because it seems to have slightly better error handling in my experience.

You can wrap your setup code in a Bluebird coroutine and then call it in place:

bluebird.coroutine(function *() {
  try {
    yield r.dbCreate(config.database.db).run();
    yield r.tableCreate('user').run();
  }
  catch (err) {
    if (err.message.indexOf("already exists") == -1)
      console.log(err.message);
  }
})();

来源：https://stackoverflow.com/questions/32851452/how-to-perform-initial-setup-in-koa-with-rethinkdb

标签

rethinkdb

koa