[MongoDB] 顯示collection 內的column

C.H. Ling — Tue, 08 Jan 2019 04:57:43 +0000

利用MongoDB 在編程上帶來不少方便, 但稍一不慎就會令到結構變得難以複雜. 示範中會利用mongoDB 讀取collection 中的property name.

加入Function isArray() 及m_sub() 作檢查Array 及recursive load.

isArray = function (v) {
  return v && typeof v === 'object' && typeof v.length === 'number' && !(v.propertyIsEnumerable('length'));
}

m_sub = function(base, value){
  for(var key in value) {
    if(key != "_id") { 
        emit(base + "." + key, null);
    if( isArray(value[key]) || typeof value[key] == 'object'){
      m_sub(base + "." + key, value[key]);
    }
}
  }
}

db.system.js.save( { _id : "isArray", value : isArray } );
db.system.js.save( { _id : "m_sub", value : m_sub } );

設定map reduce 以決定存取資料及filter 設定.

map = function(){
  for(var key in this) {
    emit(key, null);
    if( isArray(this[key]) || typeof this[key] == 'object'){
      m_sub(key, this[key]);
    }
  }
}

reduce = function(key, stuff){ return null; }

存取collection.

var collectionName="<>";
var mr = db.runCommand({
    "mapreduce" : collectionName, 
    "map" : map, 
    "reduce" : reduce,
    "out": "things" + "_keys"});
var result=db[mr.result].distinct("_id");
print(result);

MongoDB – Ling's Note

[MongoDB] 顯示collection 內的column