Most efficient way to get all value for a field in

问题:

So I'm really new to MongoDB and document storage stuffs. I'm having a hard time trying to find the most elegant and efficient solution to do the following:

I have a collection called tests. In each tests there are actions with a field owner. See below:

{
"_id" : ObjectId("528c731a810761651c00000f"),
"actions" : [
    {
        "action" : "6784",
        "owner" : "MERCHAND_1",
        "_id" : ObjectId("528c7292810761651c00000e")
    },
    {
        "action" : "1",
        "owner" : "MERCHAND_1",
        "_id" : ObjectId("528c7292810761651c00000d")
    },
    {
        "action" : "1358",
        "owner" : "MERCHAND_2",
        "_id" : ObjectId("528c7292810761651c00000c")
    }
],
"name" : "Test 1",
"product" : ObjectId("528bc4b3a0f5430812000010")

}

How can I have a list (array) of each distinct owner value using Node.js & MongoDB (I'm using mongoose driver). Is it better to do it on mongoside or node.js side? If for example I run the function on the previous table, it should return:

[
    {
      "owner":"MERCHAND_1"
    },
    {
      "owner":"MERCHAND_2"
    }
]

回答1:

You can do this with MongoDB using the command

db.runCommand({
  distinct: 'tests',
  key: 'actions.owner'
});

which gives you

{
  "values" : [
    "MERCHAND_1",
    "MERCHAND_2"
  ],
  "stats" : {...},
  "ok" : 1
}

This will include every document in the tests collection. If, however, you wanted to just check a single document, you could re-write the command as

db.runCommand({
  distinct: 'tests',
  key: 'actions.owner',
  query: { _id: ObjectId("528c731a810761651c00000f") }
});

回答2:

MongoDB supports a distinct command to do this. You can use dot notation to target fields within arrays as in this case. In the shell:

db.test.distinct('actions.owner')

outputs:

[
  "MERCHAND_1",
  "MERCHAND_2"
]