Question

我喜欢Mongo这样简单的事情,所以我希望利用它来做一些更先进的事情。在我需要之前,这样做是徒劳的:

UPDATE tbl SET a = b WHERE c <> 0

a = b part is what I can t out. 我尝试了mongodb.org,但我看不到。页: 1 WHERE a = b,但我无法发现这两种情况。

另一种选择是,所有各行各样,而不是单独更新,但我不喜欢。它必须更加简单。

感谢。

Answer 1

You want to check the documentation for updating.
http://www.mongodb.org/display/DOCS/Updating

Your code might look like:
db.tbl.update( { c:{$ne:0}}, { $set: { a : b } } );

If you need to brush up on advanced queries (e.g. using $ne), then check here:
http://www.mongodb.org/display/DOCS/Advanced+Queries

EDIT:
Apparently you can t update with data from the same document.
MongoDB: Updating documents using data from the same document

<EDIT 2(用地图压缩):

var c = new Mongo();
var db = c.getDB( db )
var s = db.getCollection( s )
s.drop();
s.save({z:1,q:5});
s.save({z:11,q:55});

db.runCommand({
mapreduce: s ,
map:function(){
  var i = this._id; //we will emit with a unique key. _id in this case
  this._id=undefined; //strange things happen with merge if you leave the id in
  //update your document with access to all fields!
  this.z=this.q;

  emit(i,this);
}, 
query:{z:1},    //apply to only certain documents
out:{merge: s } //results get merged (overwrite themselves in collection)
});

//now take a look
s.find();

友情链接