MongoDB – Updating a Single Field in an Array of Embedded Documents

mongodb

I would like to update a field in an array of embedded documents.

My sample document is:

db.students.insert(
    {
        first_name:'AA',
        last_name:'BB',
        cours_reussis:[{intitule:'PAI',note:0,name_school:'EPFC'}]
    }
)

I'd like to change the value of name_school to "ENSA" instead of "EPFC".

Best Answer

Try this. It may need small modifications based on your other variables but I think this will work:

db.students.update(
   { first_name: 'AA' },
   { $set:
      {
        "cours_reussis.0.name_school": 'ENSA'
      }
   }
)

cours_reussis is an array. The 0 is the array index.

For your reference: $set

Related Solutions

MongoDB – handling embedded documents and relations

You are not missing the point :)

The key is how many reads and how many writes do you have to do when you store/update/fetch various entities in your collections?

You are presumably constantly (daily?) creating new posts and frequently creating new comments, and very frequently querying posts.

Actions like updating authors' email are very rare compared to the above. You want to optimize the performance of reads and writes that happen hundreds or thousands of times per in your application, and worry less about performance of very infrequent actions.

Having said that, I would store the basic author information embedded in the post, but I would only have information there that must be displayed with every post. If there are additional details about the author I want to keep in its own collection, I would expect that would be details that the user needs to click additional link to see (allowing for time to do another read).

MongoDB – Searching for Array Elements Nested in Documents

Remember, MongoDB has a dynamic schema. So it is perfectly ok to store this document:

{
  "JobNumber" : "50001-01",
  "CustomerId" : "joe",
  "IdentifierNumber" : NumberLong(8812739),
  "TimesPrinted" : 0,
  "Packaging" : {"bundle":1200,"box":120,"pallet":3}
}

and this document

{
  "JobNumber" : "50001-02",
  "CustomerId" : "jane",
  "IdentifierNumber" : NumberLong(8812739),
  "TimesPrinted" : 0,
  "Packaging" : {"sack":200}
}

in the same collection.

Since, I wouldn't query for the Nth document, but for a given field in the subdocument, for example

 db.collection.find({"packaging.bundle":1200})

which would run just fine with MongoDB. The reason behind that is that if a field isn't present in a document, it is evaluated as null for a query. And null is definitely not equal to 1200.

As for the performance. It really depends on who big your collection is and how your queries look like. While the query as shown above may be rather slow in a collection containing hundred of thousands of documents (or even more) without an index, it can be extremely fast when you created an index on it, e.g.

    db.collection.ensureIndex({"packaging.bundle":1,"packaging.box":1,"packaging.pallet":1});

If you can create an index like this obviously depends on the question wether you really have arbitrary packaging or if you simply have a variety of packaging options. If the latter is the case, I'd create an index for each of the packaging options, utilizing sparse indices, e.g.

 db.collection.ensureIndex({"packaging.sack":1},{sparse:true})

This would reduce the index size, as only documents which hold the field "packaging.sack" would be contained in this index.

If you really have arbitrary fields in the documents, I wonder how you create a model for it ;)

When talking of just some ten thousands of documents, you might even get satisfying result without an index.

Best Answer

Related Solutions

MongoDB – handling embedded documents and relations

MongoDB – Searching for Array Elements Nested in Documents

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