I have a collection list such:
{username: 'somename',
friendId: '57d725d6b8b144044602bf74' <-- This a reference objectId to another doc
}
When I query docs in my collection with criteria {friendId : '57d725d6b8b144044602bf74'} I get no results back .
Any other field query works fine.
I tried to convert the value to ObjectId('57d725d6b8b144044602bf74') even though the value is just a string, still no go.
Why am I failing to search for by that type of string ?
you are trying to achieve 'self-join' in mongoDB and you seems to rely on the _id field generated by mongodb.
i would suggest you to supply custom _ID fields to the document.
eg:
{_id:"alex", name:"alex", friendID:""}
{_id"john", name"john", friendID:"alex"}
and then you can execute your queries with ease on friendID field. Give it a shot and see if this make sense for your requirement.
Related
When I query all the records, i get the results as shown below.
When i copy an ID from the result and add it in the filter, no result is found.
Here is the example filter from documentation
What am i doing wrong? mongo db got to be kidding me :/
You are not providing the data type with the query. Since your _id field is ObjectId type and you are comparing as string that is why it is not working.
Change your filter condition and convert your string id to ObjectId type.
{_id: ObjectId('yourId')}
MongoDB provides an automatic unique identifier for the _id field in the form of an ObjectId data type.
I'm building a project with MongoDB, but I'm a little bit confused on how the _id field works. My understanding is that, by default, MongoDB will generate an object of type ObjectId and assign it as the id.
However, in my server, I'm assigning an arbitrary string as the _id of an object. What I haven't quite understood yet: Is this string somehow converted to an ObjectId, or does the type of the _id field change to string?
MongoDB will generate an _id field with an ObjectId value if an _id field does not exist in the document. If you create the _id by your own, then you can use whatever datatype you like to use. MongoDB does not modify it.
The only constraint is, it must be a unique value.
I'm trying to put a prefix before the auto generated _id, to identify from which collection came an id, but I still want to use the mongo unique id generator.
So I can know that this id model_5e1a51821c9d44000089e3e0 came from the Model collection.
Is there a solution for that without messing with random string ?
Edit
The _id need to be string castable, since I use it as id in a graphQL object. I need to differentiate ids because I use an union in my schema and resolver need to know in which table to find the data.
The _id can be generated within an application with the constructor ObjectId(). If you want to add a prefix for the generated field, you can use an embedded document as a field for the _id, like this:
_id: {
idPrefix: "Model",
_id: ObjectId("5e1bd112b7f18a490a4bafb5")
}
Other way of identifying if a document is from another collection is use a separate boolean field:
{
_id: ObjectId("5e1bd112b7f18a490a4bafb5"),
isFromModel: <boolean true or false>,
...
}
There are some options available to do this, I'm just trying to tell you the way how would I do if I need this.
Step 1: You can generate the document and it will return you ObjectId (_id) .
Step 2: Take that value and prefix it with model like this.
let _id=5e1a51821c9d44000089e3e0;let new_idValue="model_"+_id;
Step3: Now update your document by _id and push new value in place of if as
this.db.document.findByIdAndUpdate(_id,{$set:{{_id:new_idValue}})
This is what you can do. If you find some best solution than mine, let me know as well. I will highly appreciate.
I have a Meteor application whereby I initially use the _id field from each record in my collection when naming list items in my template.
When get the _id field, I convert it to a string to use in the template.
Now I want to update these records in Mongo and am passing the _id back to a Meteor.method, but these are still in string format and Mongo is expecting an ObjectID(). Is there a simple way to convert this string to the ObjectID()? If not, what alternatives do I have?
Ok, found it! On the /server, within your Meteor method function do this to convert it:
var mid = new Mongo.ObjectID(str_id_sent_to_server);
From the looks of the syntax for handling mongodb related things in meteor it seems that you always need to know the collection's name to update, insert, remove or anything to the document.
What I am wondering is if it's possible to get the collection's name from the _id field of a document in meteor.
Meaning if you have a document with the _id equal to TNTco3bHzoSFMXKJT. Now knowing the _id of the document you want to find which collection the document is located in. Is this possible through meteor's implementation of mongodb or vanilla mongodb?
As taken from the official docs:
idGeneration String
The method of generating the _id fields of new documents in this collection. Possible values:
'STRING': random strings
'MONGO': random Meteor.Collection.ObjectID values
The default id generation technique is 'STRING'.
Your best option would be to insert records within a pseudo transaction where the second step is to take the id and collection name to feed it into a reference collection. Then, you can do your lookups from that.
It would be pretty costly, though to construct your find's but might be a pattern worthwhile exploring if you are building an app where your users will be creating arbitrary data patterns.
You could accomplish this by doing a findOne on all of the collections:
var collectionById = function(id) {
return _.find(_.keys(this), function(name) {
if (this[name] instanceof Meteor.Collection) {
if (this[name].findOne(id)) {
return true;
}
}
});
};
I tested this on both the client and the server and it seemed to work when run in the global context.