嘿，如果用户在两个集合中都是唯一的，请使用函数findOne()，因为find()返回一个游标.因此，要在mongoDB控制台中实现两个对象的合并，可以使用以下代码:

Hey if the user is unique in both collections use function findOne(), because find() returns a cursor. So to achieve a merge of two objects in the mongoDB console you can use the bellow code:

function mergeObjects(a,b) {
    res = new Object();

    for (attr in a) 
          res[attr] = a[attr];
    for (attr in b)
          res[attr] = b[attr];

    // only if you wanna save it in a document again
    delete res["_id"];
    return res;
 }

a = db.users.findOne({"username" : 'abc@xyz.com'})
b = db.tasks.findOne({"username" : 'abc@xyz.com'})
c = mergeObjects(a,b)

希望这可以解决您的问题.

Hopefully this solve your problems.