CODEWITHSUNDEEP
shellmongodbmongo-shell
user775171
user775171

Reputation:

How do I add another value to a dictionary in MongoDB?

Here's an example of what I'm trying to do, as I can't explain what I mean.

I execute this in the mongo CLI: db.posts.insert({name: "Hello, world!, body: "Here's my first blog post. Happy reading!", comments: []}). What I want to do is update that entry to add a comment to the comments dictionary.

How would I achieve this using db.posts.update()?

Upvotes: 6

Views: 16575

Answers (2)

mikeho
mikeho

Reputation: 7000

The OP's question and example don't match. He actually wants to insert a field into an array within the document, which means that

db.posts.update({name: "Hello, world!" }, { $push: {comments: "First comment!"}});

works just fine.

However, if you want to add a value or subdocument to a dictionary, you would use the $set command. Take this document as our example:

{
    "_id": {
        "$oid": "538420b2862a656e9e99fc93"
    },
    "name": "Farmer John",
    "items": {
        "peaches": 5,
        "bananas": 10
    }
}

Let's say you wish to add "apples": 2 to the items. The command would be

db.collection.update({"name": "Farmer John"},
                     {"$set": {"items.apples": 2}});

Your document would then look like:

{
    "_id": {
        "$oid": "538420b2862a656e9e99fc93"
    },
    "name": "Farmer John",
    "items": {
        "peaches": 5,
        "bananas": 10,
        "apples: 2
    }
}

Note that this works with inserting subdocument as well, so we can modify the original example:

{
    "_id": {
        "$oid": "538420b2862a656e9e99fc93"
    },
    "name": "Farmer John",
    "items": {
        "peaches": {
            "yellow": 5,
            "white": 3
        }
    }
}

And let's insert 4 granny smith apples and 8 fuji apples.

db.collection.update({"name": "Farmer John"},
                     {"$set": {"items.apples": {"fuji": 8, "granny smith": 4}}});

Our document would now be:

{
    "_id": {
        "$oid": "538420b2862a656e9e99fc93"
    },
    "name": "Farmer John",
    "items": {
        "peaches": {
            "yellow": 5,
            "white": 3
        },
        "apples": {
            "fuji": 8,
            "granny smith": 4
        }
    }
}

One last comment: note that if the subdocument or field already exists, then it will be overridden by the $set command.

Upvotes: 17

Shashank Mehta
Shashank Mehta

Reputation: 120

For an object like:

{
  name: "Hello, world!",
  content: "This is my first post"
}

if you now run

db.posts.update({name: "Hello, world!"}, {name: "First post"});

this is what would be the result:

{
  title: "First post"
}

The content attribute will be removed as there is no replacement values provided. I'm mentioning this as this is a common error.

So if you want to "add" an attribute, you need to run:

db.posts.update({name: "Hello, world!" }, { $push: {comments: "First comment!"}});

$push is used if you are appending data to an array. If its a normal field use $set.

Reference: http://www.mongodb.org/display/DOCS/Updating

Upvotes: -3

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