Mongodb use array as unique key - mongodb

I want to make sure I only have one instance a documents that is an agreement between to entities... I may have modeled this wrong, so Im looking for suggestions if there is a better way to do this.
but in essence, the document looks like this.
{
_id:objectid,
entity_Ids: [objectid]
}
I was curious what's the best way to make sure the array is unique so id I do
db.agreements.insert(entity_Ids:[1,2]) and there is already a 1,2 I'll get a conflict.
I could have done it like this :
{
_id:objectid,
entity1: objectid,
entity2: objectid
}
but then I'd always have to do a check of where entit1=1 or entity2=1 or entity1=2 or entity2=2

you can create unique index on any key in the document
so in your case try
db.myCollection.createIndex({entity_Ids: 1},{unique: true});

Related

Put a prefix for ObjectID for MongoDB _id field

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.

Mongodb find where exists in other collection

I have a user collection and a document one, where entries have a owner field that is a reference to the user ObjectId(_id).
I'm amazed I can't find all users that have at least a document...
I tried:
db.getCollection('user').find({_id: {
$in: db.getCollection('document').find({}).map(function(f) {return f.owner}).distinct()
}});
but it won't work and anyway it really feels like not the correct way to do this since all documents need to be loaded in memory.
I tried to use http://www.querymongo.com but it really did not help.
Thanks

How do I make a mongo query for something that is not in a subdocument array of heterodox size?

I have a mongodb collection full of 65k+ documents, each one with a properties named site_histories. The value of it is an array that might be empty, or might not be. If it is not empty, it will have one or more objects similar to this:
"site_histories" : "[{\"site_id\":\"129373\",\"accepted\":\"1\",\"rejected\":\"0\",\"pending\":\"0\",\"user_id\":\"12743\"}]"
I need to make a query that will look for every instance in the collection of a document that does not have a given user_id.
I'm pretty new to Mongo, so I was trying to make a query that would find every instance that does have the given user_id, which I was then planning on adding a "$ne" to, but even that didn't work. This is the query I was using that didn't work:
db.test.find({site_histories: { $elemMatch: {user_id: '12743\' }}})
So can anyone tell me why this query didn't work? And can anyone help me format a query that will do what I need the final query to do?
If your site_histories really is an array, it should be as simple as doing:
db.test.find({"site_histories.user_id": "12743"})
That looks in all the elements of the array.
However, I'm a bit scared of all those backslashes. If site_histories is a string, that won't work. It would mean that the schema is poorly designed, you'd maybe try with $regex

Does Mongo make a mistake like this?

Say I have a User Document, filled with arrays of ObjectIds.
They are references to documents in another collection.
I want to load all things from a particular user's array. So I do:
find({ _id: $in : someArrayOfObjectIds})
It's possible that certain references reference something that has been deleted.
So the resulting array of the above "find" call can be smaller then the someArrayOfObjectIds.
So for all the ObjectIds not found can I now safely assume that that document does not exist anymore, or can my query just fail to find a document (does mongo make a mistake).
Yes, you can safely assume that missing documents do not exist. By the way, your query is invalid. Should be this:
find({ _id: {$in : someArrayOfObjectIds}})
or can my query just fail to find a document
If it was possible, no one would use it. Pen and paper approach is a safer alternative that DB that makes such mistakes :)

MongoDB: Unique Key in Embedded Document

Is it possible to set a unique key for a key in an embedded document?
I have a Users collection with the following sample documents:
{
Name: "Bob",
Items: [
{
Name: "Milk"
},
{
Name: "Bread"
}
]
},
{
Name: "Jim"
},
Is there a way to create an index on the property Items.Name?
I got the following error when I tried to create an index:
> db.Users.ensureIndex({"Items.Name": 1}, {unique:true});
E11000 duplicate key error index: GroceryGuruApp.Users.$Items.Name_1 dup key: {
: null }
Any suggestions? Thank you!
Unique indexes exist only across collection. To enforce uniqueness and other constraints across document you must do it in client code. (Probably virtual collections would allow that, you could vote for it.)
What are you trying to do in your case is to create index on key Items.Name which doesn't exist in any of the documents (it doesn't refer to embedded documents inside array Items), thus it's null and violates unique constraint across collection.
You can create a unique compound sparse index to accomplish something like what you are hoping for. It may not be the best option (client side still might be better), but it can do what you're asking depending on specific requirements.
To do it, you'll need to create another field on the same level as Name: Bob that is unique to each top-level record (could do FirstName + LastName + Address, we'll call this key Identifier).
Then create an index like this:
ensureIndex({'Identifier':1, 'Items.name':1},{'unique':1, 'sparse':1})
A sparse index will ignore items that don't have the field, so that should get around your NULL key issue. Combining your unique Identifier and Items.name as a compound unique index should ensure that you can't have the same item name twice per person.
Although I should add that I've only been working with Mongo for a couple of months and my science could be off. This is not based on empirical evidence but rather observed behavior.
More on MongoDB Indexes
Compound Keys Indexes
Sparse Indexes
An alternative would be to model the items as a hash with the item name as the key.
Items: { "Milk": 1, "Bread": 1 }
I'm not sure about whether you're trying to use the index for performance or purely for the constraint. The right way to approach depends on your use cases, and determining whether the atomic operations are enough to keep your data consistent.
The index will be across all Users and since you asked it for 'unique', no user will be able to have two of the same named item AND no two users will be able to have the same named Item.
Is that what you want?
Furthermore, it appears that it's objecting to two Users having a 'null' value for Items.Name, clearly Jim does, is there another record like that?
It would be unusual to require uniqueness on an indexed collection like this.
MongoDB does allow unique indexes where it indexes only the first of each value, see
http://www.mongodb.org/display/DOCS/Indexes#Indexes-DuplicateValues, but I suspect the real solution is to not require uniqueness in this case.
If you want to ensure uniqueness only within the Items for a single user you might want to try the $addToSet option. See http://www.mongodb.org/display/DOCS/Updating#Updating-%24addToSet
You can use use findAndModify to create a sequence/counter function.
function getNextSequence(name) {
var ret = db.counters.findAndModify({
query: { _id: name },
update: { $inc: { seq: 1 } },
new: true,
upsert: true
});
return ret.seq;
}
Then use it whenever a new id is needed...
db.users.insert({
_id: getNextSequence("userid"),
name: "Sarah C."
})
This is from http://docs.mongodb.org/manual/tutorial/create-an-auto-incrementing-field/. Check it out.