How to find and insert into sub document array list in MongoDB?

Question

I want to insert a value to the array in the array of the sub document when the value is not already there.I have a collection like this

{
"_id" : ObjectId("53993f67ccbc960c7d05b74f"),
"groups" : [
    {
        "groupName" : "Default",
        "groupMembers" : [ ]
    },

    {
        "groupMembers" : [ ],
        "groupName" : "Family"
    },
    {
        "groupName" : "Friends",
        "groupMembers" : ["jack" ]
    }
],
"userName" : "krishna",
}

Now i want to find the a value in Friends group and if the value is not there and it should be inserted.

Neil Lunn · Accepted Answer · 2014-06-12 08:37:55Z

3

You want the $addToSet operator:

db.groups.update(
    { "userName": "krishna", "groups.groupName": "Friends" },
    {
        "$addToSet": { "groups.$.groupMembers": "jack" }
    }
)

Also using the same positional $ operator to match the required array element, you use $addToSet which will "push" the element onto the array if it does not exist. If it does exist then there is no update performed.

edited Jun 12, 2014 at 8:37

answered Jun 12, 2014 at 8:27

Neil Lunn

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5 Comments

Mulagala Over a year ago

@Nill Lunn, I am getting the following error Invalid modifier specified $addToset

Neil Lunn Over a year ago

@Mulagala Typo in the code sample. It was typed correctly everywhere else.

Mulagala Over a year ago

@Nill Lunn, can we count the matched documents, because i need to warn when there is already same member in list, Because i may face a problem while deleting a member not in list.So first i need to find a member in list

Neil Lunn Over a year ago

@Mulagala See here. The same basic principle applies in all drivers that support the methods. In the shell you will see the results returned immediately with MongoDB 2.6 and upwards.

Web User Over a year ago

@NeilLunn I have a similar requirement where I need to add/update/delete in arrays of sub-documents as well as add/update/delete in arrays of sub-documents inside the first level of sub-document arrays. I asked a question about this on SO today, because I was getting really confused.

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