MongoDB mongoid 如果 map 只有一条记录, 就不会去 reduce?
def self.cities
cities_map = <<MAP
function() {
if (typeof this.location !== 'undefined' && this.location !== null)
emit(this.location, { login: this.login, count: 1 });
}
MAP
cities_reduce = <<REDUCE
function(key, values) {
var sum = 0;
var logins = [];
values.forEach(function(value) {
sum += value.count;
logins.push(value.login)
});
return { logins: logins, sum: sum };
};
REDUCE
self.collection.map_reduce(cities_map, cities_reduce, :out => "mr_results")
end
结果只有一条记录的香港没有进行 reduce
1.9.2p290 :001 > @cities = User.cities.find().to_a => [{"_id"=>"杭州", "value"=>{"logins"=>["lainuo", "winfield"], "sum"=>2.0}}, {"_id"=>"香港", "value"=>{"login"=>"cersei", "count"=>1.0}}]
虽然说只有一条记录不进行 reduce 可以算是合理，不过这样结果不大好处理啊，有没有办法强制进行 reduce 呢？
目前我是这么变通了一下：
cities_map = <<MAP
function() {
if (typeof this.location !== 'undefined' && this.location !== null)
emit(this.location, { logins: [this.login], count: 1 });
}
MAP
cities_reduce = <<REDUCE
function(key, values) {
var count = 0;
var logins = [];
values.forEach(function(value) {
count += value.count;
logins.push(value.logins.pop());
});
return { logins: logins, count: count };
};
REDUCE
不知道有没有更好的办法。