Writing reduce function in couchbase

问题

This is my first attempt at couchbase. My json doc looks like this:

{
   "member_id": "12345",
   "devices": [
       {
           "device_id": "1",
           "hashes": [
               "h1",
               "h2",
               "h3",
               "h4"
           ]
       },
       {
           "device_id": "2",
           "hashes": [
               "h1",
               "h2",
               "h3",
               "h4",
               "h5",
               "h6",
               "h7"
           ]
       }
   ]
}

I want to create a view which tells me all member_ids for a given hash.

Something like this:

h1["12345","233","2323"]  //233,2323 are other member id    
h2["12345"]

The member_id should appear once in the set.

I wrote a map function

function (doc, meta) {
  for(i=0;i< doc.devices.length;i++)
  {
    for(j=0;j< doc.devices[i].hashes.length;j++)  {
        emit(doc.devices[i].hashes[j],null)
          }
  }
}

and this returns

h1 "12345"
h1 "12345"
h2 "12345"
h1 "233"

but I'm not able to move forward from here. How should I change my map function to reduce the result?

回答1:

Map function. Mostly yours, but emits meta.id as a value.

function(doc, meta) {
  for(i=0; i< doc.devices.length; i++) {
    for(j=0; j< doc.devices[i].hashes.length; j++)  {
      emit(doc.devices[i].hashes[j], meta.id)
    }
  }
}

Reduce function. Is just return unique array from values (taken from https://stackoverflow.com/a/13486540/98509)

function(keys, values, rereduce) {
  return values.filter(function (e, i, arr) {
    return arr.lastIndexOf(e) === i;
  });
}

来源：https://stackoverflow.com/questions/16177986/writing-reduce-function-in-couchbase