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MongoDB Database, equivalent for SELECT column1, column2 FROM tbl

From my MongoDB I want the equivalent for

  SELECT column1, column2
  FROM tbl

With this code I get all the 'rows' but also all the 'columns'

  DBCollection collection = database.getCollection("names");
  DBCursor cursor = collection.find();

I for example would like all the 'rows' but only the 'columns': id, name, age

How would I do this?

Thanks for any help!!

like image 897
Marc Stevens Avatar asked Aug 26 '11 14:08

Marc Stevens


2 Answers

db.collection.find({}, {_id: 1, name: 1, age: 1})

The first argument to find (the predicate) is your selection criteria, e.g.

db.collection.find({age: {$gte: 21}})

The second limits the fields you retrieve, so for the names over everyone 21 or older:

db.collection.find({age: {$gte: 21}}, {name: 1})

The field selector always pulls back _id unless you specifically turn it off:

db.collection.find({}, {_id: 0})

However, Mongo will not check for field existence by default. If you want to select certain fields, and match only results that have those fields, you will want to use:

db.collection.find({ age: { $exists: true } })

The MongoDB website has a more detailed description of the .find() function!

like image 54
cjohn Avatar answered Sep 27 '22 20:09

cjohn


Thanks!, I fixed it with the code below.

    BasicDBObject select = new BasicDBObject();
    select.put("id", 1);
    select.put("name", 1);
    select.put("age", 1);
    collection.find(new BasicDBObject(), select);

Above code gives me all the records, with only the column names as above.

like image 33
Marc Stevens Avatar answered Sep 27 '22 19:09

Marc Stevens