获取集合中所有键的名称 [英] Get names of all keys in the collection

问题描述

我想获取MongoDB集合中所有键的名称.

I'd like to get the names of all the keys in a MongoDB collection.

例如，从此:

db.things.insert( { type : ['dog', 'cat'] } );
db.things.insert( { egg : ['cat'] } );
db.things.insert( { type : [] } );
db.things.insert( { hello : []  } );

我想获得唯一的密钥:

type, egg, hello

推荐答案

您可以使用MapReduce做到这一点:

You could do this with MapReduce:

mr = db.runCommand({
  "mapreduce" : "my_collection",
  "map" : function() {
    for (var key in this) { emit(key, null); }
  },
  "reduce" : function(key, stuff) { return null; }, 
  "out": "my_collection" + "_keys"
})

然后在结果集合上运行，以便找到所有键:

Then run distinct on the resulting collection so as to find all the keys:

db[mr.result].distinct("_id")
["foo", "bar", "baz", "_id", ...]

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