mongoDB update multiple fields in single array element (from form)

Question

I've seen many variations on this question, but none for this specific issue. Consider the following document:

{
    "class" : "english101",
    "students" : [
        {
            "name" : "julie",
            "age" : 32,
            "gpa" : "3.4"
        },
        {
            "name" : "heather",
            "age" : 34,
            "gpa" : "3.8"
        }
    ]
}

I'd like to update BOTH the name and age fields simultaneously. Here's what I'm trying:

db.test.update(
    {
        'class':'english101', 
        'students.name':'julie'
    },
    {
        $set: {
            'students.$': {
                'name':'jules',
                'age':'31'
            }
         }
     }
 )

The result is this:

{
    "class" : "english101",
    "students" : [
        {
            "name" : "jules",
            "age" : "31",
            # GPA IS GONE!
        },
        {
            "name" : "heather",
            "age" : 34,
            "gpa" : "3.8"
        }
    ]
}

The PROBLEM is that instead of the expected update and $set behavior it replaces the whole array item, instead of just updating the supplied fields.

How should I be doing this?

Salvador Dali · Accepted Answer · 2015-04-26 02:37:40Z

1

In your case you update it with an object, which overwrites everything. Here is a correct approach.

 db.test.update({
      'class':'english101', 
      'students.name':'julie'
 },{
      $set: {
          'students.$.name': 'jules',
          'students.$.age' : 31
      }
 })

answered Apr 26, 2015 at 2:37

Salvador Dali

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3 Comments

Scott Over a year ago

Guess I was taking a shortcut. Still would be cool to be able to do that :)

Salvador Dali Over a year ago

@vfxcode then how would you update the whole object :-)? This behavior is expected.

Scott Over a year ago

I was just referring to the same way you can use $set to do a basic update and only supply the changing fields: db.test.update({"_id" : ObjectId("553c6c9216a0c2f8cbb35e7d")}, {$set: {'school':'yale', 'class':'economics101'}}). It doesn't replace the whole document.

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