suppose I have the following datastructure:
var user = {_id: 'foo', age: 35};
var post = {_id: '...', author: {$ref: user, $id: 'foo'},...};
How can I query all posts which references user[foo]? I tried the following but not work:
db.post.find('author._id': 'foo');
var u = db.user.find({_id: 'foo'});
db.post.find('author': u);
neither can I find the answer from the official document and google!
Anyone has any idea?
Got it:
db.post.find({'author.$id': 'foo'})
This db.post.find('author.$id': 'foo') has missing the {}, so the correct sentence is:
db.post.find({'author.$id': 'foo'})
Also this can be achieved with:
db.post.find({'author': DBRef("user", ObjectId('foo'))})
But is more compact and practical the first way.
You can use the .$id reference but it will ignore any indexes on those fields.
I would suggest ignoring that method unless you are querying it directly via the terminal or want to look up something quickly. In using large collections you will want to index the field and query it using the below method.
If you want to use an index query using the following:
db.post.find('author' : { "$ref" : 'user', "$id" : 'foo' , "$db" :'database_name' })
If foo is an object id
db.post.find('author' : { "$ref" : 'user', "$id" : ObjectId('foo') , "$db" :'database_name' })
You can create an index on author by
db.post.ensureIndex( {'author' : 1 } );
For anyone looking for a Java solution to this then if you are using mongojack its really easy:
collection.find(DBQuery.is("user", new DBRef(user.getId(), User.class)));
Where collection is a JacksonDBCollection.
In mongoengine you should just use the instance of the referenced object. It should have the ID set.
Suppose the author is the Author document instance. So using this:
Post.objects(author__eq=author)
you can go through all posts of this author.
Post.author should be defined as ReferenceField
Using Mongo 2.4.1 version
This is how you do it on command line for OLA collection where #DBRef dbrefName
db.OLA.find({"dbrefName.someFieldValue" : "Personal"});
Exact query
db.OLA.find({"dbrefName.$id" : ObjectId("1234")});
Related
I am having trouble understanding how new field:value objects are added to mongo databases.
Say I have the following document:
var people={'firstname': 'John','surname':'Smith',
'favouritefood':[{'fruit':'apples','drink':'coffee'}]}
how do I add 'vegetable':'broccoli' to 'favourite food' so it looks like this:
{'firstname': 'John','surname':'Smith',
'favouritefood':[{'fruit':'apples','drink':'coffee','vegetable':'broccoli'}]}
If I type:
people.findOneAndUpdate({'firstname':'John'},
{$push {favouritefood: {vegetable:broccoli}}},
{upsert:true})
it gives me this:
{'firstname': 'John','surname':'Smith',
'favouritefood':[{'fruit':'apples','drink':'coffee'},{'vegetable':'broccoli'}]}
and if I try:
people.findOneAndUpdate({'favoritefood':'apples'},
{$push {vegetable:broccoli}}},
{upsert:true})
it says:
'$push' is empty. You must specify a field like so: {$push: {<field>: ...}}
Any help is greatly appreciated!
I think you will be able to update the favouritefood array first object following this syntax
But i suggest you the same that people in the comments, change your structure to one more natural in mongoDB. Consider each category of food as an element of the array not an object field of the first element.
Background: I have a mongo database named test with a collection called collection. There is a single document in test.collection:
{ "_id" : ObjectId("64e4a6f9d1d7ba45250dc2c1"), "key" : "value"}
Question: Using Mongoose, what is a way to grab the lone document found in test.collection, convert it into a javascript object, and to identify it with the variable object? For example, we should have that
console.log(object.key)
returns "value".
EDIT : I have tried the following, which didn't work:
var Schema = mongoose.Schema;
var Model = db.model('Model', mongoose.Schema({}),'collection');
var doc = Model.findOne();
console.log(doc.key); // doesn't show "value" as expected
Do it this way (as stated on my comment):
Model.find(function (err, docs) {
if (err) return console.error(err);
console.log(docs[0].key);
});
I also recommend taking another look to the docs, it's always good to refresh the basic concepts.
I want to create a PATCH method for my API but there is something I don't understand. Imagine I have the following document in my MongoDB database:
{
_id : ObjectId(1234...),
name : "bob",
age : 30
}
Now I would like to update this document but I don't know what keys my API will receive. So imagine I make a request in order to change the age but also add a last_name.
The request result would be like this:
{
_id : ObjectId(1234...),
name : "bob",
last_name : "smith",
age : 44
}
The main problem here is that I don't know the arguments I will receive.
My goal is to update the values of the existing keys and add the keys that are not in the document.
Any idea?
Thanks
You want to use the $set operator.
What this does is only updates the keys that are sent in the update query. Without $set, it will overwrite the whole object, which is obviously not what you want.
app.patch('/user/:id', function (req, res) {
var updateObject = req.body; // {last_name : "smith", age: 44}
var id = req.params.id;
db.users.update({_id : ObjectId(id)}, {$set: updateObject});
});
I'm assuming a couple things here:
You are using express.
You are using either the mongodb driver or mongojs npm module
I am modelling two types of events (events and subevents) in a MongoDB like this:
var EventSchema = mongoose.Schema({
'name' : String,
'subEvent' : [ SubeventSchema ]
});
var SubeventSchema = mongoose.Schema({
'name' : String
});
Now when I query a subevent I want to be able to also retrieve data about its corresponding superevent, so that some example data retrieved using Mongoose population feature could look like this:
EventModel.findOne({
name : 'Festival'
})
.populate('subEvent')
.execute(function (err, evt) { return evt; });
{
name : 'Festival',
subEvent: [
{ name : 'First Concert' },
{ name : 'Second Concert' }
]
}
EventModel.findOne({
'subEvent.name' : 'FirstConcert'
}, {
'subEvent.$' : 1
})
.populate('superEvent') // This will not work, this is the actual problem of my question
.execute(function (err, subevt) { return subevt; });
{
name: 'First Concert',
superEvent: {
name: 'Festival'
}
}
A solution I can think of is not to embed but to reference like this:
var EventSchema = mongoose.Schema({
'name' : String,
'subEvent' : [ {
'type' : mongoose.Schema.Types.ObjectId,
'ref' : 'SubeventSchema'
} ]
});
var SubeventSchema = mongoose.Schema({
'name' : String,
'superEvent' : {
'type' : mongoose.Schema.Types.ObjectId,
'ref' : 'EventSchema'
}
});
I am looking for a solution based on the first example using embedded subevents, though. Can this be achieved and in case yes, how?
I think your mental model of document embedding isn't correct. The major misunderstanding (and this is very common) is that you "query a subevent" (query an embedded document). According to your current Event schema, a Subevent is just a document embedded in an Event document. The embedded SubEvent is not a top-level document; it's not a member of any collection in MongoDB. Therefore, you don't query for it. You query for Events (which are the actual collection-level documents in your schema) whose subEvents have certain properties. E.g. one way people translate the query
db.events.find({ "subEvent" : { "name" : "First Concert" } })
into plain English is as "find all the subevents with the name "First Concert". This is wrong. The right translation is "find all events that have at least one subevent whose name is "First Concert" (the "at least one" part depends on knowledge that subEvent is an array).
Coming back to the specific question, you can hopefully see now that trying to do a populate of a "superevent" on a subevent makes no sense. Your queries return events. The optimal schema, be it subevents embedded in events, one- or two-way references between events and subevents documents in separate collections, or events denormalized into the constituent subevent documents, cannot be determined from the information in the question because the use case is not specified.
Perhaps this is a situation where you need to modify your thinking rather than the schema itself. Mongoose .populate() supports the basic ideas of MongoDB "projection", or more commonly referred to as "field selection". So rather than try to model around this, just select the fields you want to populate.
So your second schema form is perfectly valid, just change how you populate:
EventModel.find({}).populate("subEvent", "name").execute(function(err,docs) {
// "subevent" array items only contain "name" now
});
This is actually covered in the Mongoose documentation under the "populate" section.
I'm using sails-mongo in my project and i need to execute one query in an embedded collection.
My data are something like the following:
{
"_id" : ObjectId("53906c6254f36df504e99b8f"),
"title" : "my post"
"comments" : [
{
"author" : "foo",
"comment" : "foo comment"
},
{
"author" : "bar",
"comment" : "bar comment"
}
],
"createdAt" : ISODate("2014-06-05T13:10:58.365Z"),
"updatedAt" : ISODate("2014-06-05T13:10:58.365Z")
}
for example, i need to extract the comments of author foo.
Apparently sails does not support this feature yet, so i was considering using the object db of mongodb-native to make this kind of query.
As sails-mongo uses mongodb-native, can i have access to db object in my sails project? Or i will need build a new connection using mongodb-native?
If anyone has a better idea I'd be grateful. Thanks
If all you need to do is access the embedded comments, Waterline should work fine. Just do a normal find or findOne, and the comments should be accessible on the returned objects.
If you need to query the comments, e.g. to find Posts with comments by a certain author, you can access the underlying mongodb-native collection using the .native() method of your Sails model class:
Post.native(function(err, collection) {
if (err) {
// handle error getting mongo collection
}
collection.find({'comments.author':'foo'}).toArray(function(err, results) {
// Do something with results
});
});