Plans for $elemMatch and $ operator? about forerunnerdb HOT 3 CLOSED

Hi ya,

So I think that the $elemMatch functionality already exists as ForerunnerDB simply accepts a query against an array field and will scan the sub-documents to ensure they match. If any sub-documents match then the whole parent document is included in the result which kinda makes $elemMatch irrelevant (except for compatibility).

For example if we have a collection with the documents:

[{
    _id: '1',
    arr: [{
        _id: 'jim',
        name: 'Jim'
    }, {
        _id: 'bob',
        name: 'Bob'
    }]
}, {
    _id: '2',
    arr: [{
        _id: 'alice',
        name: 'Alice'
    }, {
        _id: 'simon',
        name: 'Simon'
    }]
}]

Then query it with:

{
    arr: {
        name: 'Jim
    }
}

The result will return the document with _id: '1'.

This is what I understand that $elemMatch already does but please correct me if I am wrong! :)

The roadmap item relates to updating documents rather than querying them and it might be that we don't actually need that functionality as there is already a way to identify sub-documents in updates.

from forerunnerdb.

I think to your point update functions are there easiest way to illustrate and most applicable. So I have the following query in Mongoose:

Project.update({"_id":data.id, "categories": {$elemMatch: {_id:data.categoryid}}},{$set: {
                "categories.$.name" : data.name,
                "categories.$.description" : data.description
}}, function(){
                // next...
});

This lets me target a record (which I will call project) with the matching id that also matches the id of a nested array called categories. If those criteria match, it updates the value for name and description for only that specific matched record under the category array, which is again nested in the project.

So to use your structure above, by doing a:

Project.update({"_id": 1, "arr": {$elemMatch: {_id: "bob"}}},{$set: {
                "arr.$.name" : "Robert"
}}, function(){
                // next...
});

I would get an updated collection of:

[{
    _id: '1',
    arr: [{
        _id: 'jim',
        name: 'Jim'
    }, {
        _id: 'bob',
        name: 'Robert'
    }]
}, {
    _id: '2',
    arr: [{
        _id: 'alice',
        name: 'Alice'
    }, {
        _id: 'simon',
        name: 'Simon'
    }]
}]

Again, I think this works closely with the $set operator which is part of the update process. Can you give me an example of identifying sub documents in updates? Specifically using arrays as sub documents? Maybe I missed something in the documentation. :)

from forerunnerdb.

$elemMatch (projection) has been added to ForerunnerDB for find() calls. Calls to update() still need to have that functionality added specifically with $elemMatch operators, however a I mentioned above you can specify a sub-array document to be updated already.

from forerunnerdb.