I've created a document model where I'm using a field named id in addition to MongoDB's auto-generated _id field.
Will this cause any problems for me down the line?
I can imagine a circumstance where something in Mongo might assume my "id" property is referring to "_id" instead, when it isn't (like some API feature with the good intention of preventing you from having to type that underscore, where in my case such a well-meaning feature would be a disaster).
Will this be ok?
Related
I'm Following this Doc
http://docs.doctrine-project.org/projects/doctrine-mongodb-odm/en/latest/tutorials/getting-started.html
And
http://symfony.com/doc/current/bundles/DoctrineMongoDBBundle/index.html
When I Save My Document, I have two Collection
like this:
{
"_id" : ObjectId("5458e370d16fb63f250041a7"),
"name" : "A Foo Bar",
"price" : 19.99,
"posts" : [
{
"$ref" : "Embedd",
"$id" : ObjectId("5458e370d16fb63f250041a8"),
"$db" : "test_database"
}
]
}
I'd like have
{
"_id" : ObjectId("5458e370d16fb63f250041a7"),
"name" : "A Foo Bar",
"price" : 19.99,
"posts" : [
{
"mycomment" :"dsdsds"
" date" : date
}
]
}
I want denormalization my data. How Can i Do it?
Can I use Methods like $push,$addToSet etc of mongoDb?
Thanks
Doctrine ODM supports both references and embedded documents.
In your first example, you're using references. The main document (let's assume it's called Product) references many Post documents. Those Post documents live in their own collection (for some reason this is named Embedd -- I would suggest renaming that if you keep this schema). By default, ODM uses the DBRef convention for references, so each reference is itself a small embedded document with $ref, $id, and $db fields.
Denormalization can be achieved by using embedded documents (an #EmbedMany mapping in your case). If you were embedding a Post document, the Post class should be mapped as an #EmbeddedDocument. This tells ODM that it's not a first-class document (belonging to its own collection), so it won't have to worry about tracking it by _id and the like (in fact, embedded documents won't even need identifiers unless you want to map one).
My rule of thumb for deciding to embed or references has generally been asking myself, "Will I need this document outside of the context of the parent document?" If a Post will not have an identity outside of the Product record, I'm comfortable embedding it; however, if I find later that my application also wants to show users a list of all of their Posts, or that I need to query by Posts (e.g. a feed of all recent Posts, irrespective of Product), then I may want to reference documents in a Posts collection (or simply duplicate embedded Posts as needed).
Alternatively, you may decide that Posts should exist in both their own collection and be embedded on Product. In that case, you can create an AbstractPost class as a #MappedSuperclass and define common fields there. Then, extend this with both Post and EmbeddedPost sub-classes (mapped accordingly). You'll be responsible for creating some code to generate an EmbeddedPost from a Post document, which will be suitable for embedding in the Product.posts array. Furthermore, you'll need to handle data synchronization between the top-level and embedded Posts (e.g. if someone edits a Post comment, you may want all the corresponding embedded versions updated as well).
On the subject of references: ODM also supports a simple option for reference mappings, in which case it will just store the referenced document's _id instead of the larger DBRef object. In most cases, having DBRef store the collection and database name for each referenced document is quite redundant; however, DBRef is actually useful if you're using single-collection inheritance, as ODM uses the object to store extra discriminator information (i.e. the class of the referenced object).
I use mongo_insert() three times to insert my data in three different collections. The problem is that the "_id" field must be exactly the same in each of the collections, but I do not know how to (ideally) recover and reuse the "_id" field generated in my first mongo_insert...
Please, advice me how to do it.
Normally, you could have different field, like CustomId for your private needs, and leave _id for mongo generation.
But if you still need it to be exactly the same - there could be 2 variants:
1) setting custom generated _id do each doc.
2) Save first doc, then read it again, check it's _id and set it to the other docs.
Why is there an underscore in front of the MongoDb document id ?
Why not call it "id" instead of "_id" ?
Is this part of a naming convention I'm not aware of ?
You may notice that MongoDB has a lot of functions (in the shell) and fields that start with an understore as a designation that they are internal or special and not user provided.
If you have your own "ID" then you can store it as "id" and still use the provided-by-MongoDB _id field although you are not required to use the ObjectId that MongoDB generates - you could store your own natural primary key in the "_id" field which will have a unique index on it always.
for testing purposes I need to create manually some objects in a MongoDB. My Class has a reference field to another class. The referred object already exists.
I tried to put the Mongo-ID of my existing object as a value in my new object but I get the following error:
A ReferenceField only accepts DBRef: ['attribute'])
Now my question: Where do I get or find this DBRef?
An example:
I have a user in my db. I want to create a group which has the existing user as "creator". When I put the user-ID into the creator-field I get the error...
Edit:
I just found this link MongoDB - DBRef but the solution does not work for me...
item : {"$ref" : "fruit", "$id" : "1"}
My code is like this:
{ "name" : "MyGroup", "created_at" : "2011-05-22T00:46:38", "creator": { "$ref": "user", "$id": "501bd5ac32f28a1278e54435" } }
Another edit:
Even the Mongo doc says I'm using the right format... http://www.mongodb.org/display/DOCS/Mongo+Extended+JSON. But still not working.
In the question you referenced, the user is using a numeric string as their document ID. In your case, it looks like you're working with the more-common ObjectId but inserting it as a string. Assuming you're using PyMongo, you probably want to use the ObjectId class for the $id property of the DBRef.
If you know all such references are going to point to the same DB and collection, it may make sense to use manual references (just storing the target document's _id) instead of DBRef objects. This is explained in more detail in the Database References documentation.
Using Java ... not that it matters.
Having a problem and maybe it is just a design issue.
I assign "_id" field to all of my documents, even embedded ones.
I have a parent document ( and the collection for those ) which has an embedded document
So I have something like:
{ "_id" : "49902cde5162504500b45c2c" ,
"name" : "MongoDB" ,
"type" : "database" ,
"count" : 1 ,
"info" : { "_id" : "49902cde5162504500b45c2y",
"x" : 203 ,
"y" : 102
}
}
Now I want to have another document which references my "info" via a DBRef, don't want a copy. So, I create a DBRef which points to the collection of the parent document and specifies the _id as xxxx5c2y. However, calling fetch() on the DBRef gives a NULL.
Does it mean that DBRef and fetch() only works on top level collection entry "_id" fields?
I would have expected that fetch() would consume all keys:values within the braces of the document .. but maybe that is asking too much. Does anyone know?? Is there no way to create cross document references except at the top level?
Thanks
Yes, your DBRef _id references need to be to documents in your collection, not to embedded documents.
If you want to find the embedded document you'll need to do a query on info._id and you'll need to add an index on that too (for performance) OR you'll need to store that embedded document in a collection and treat the embedded one as a copy. Copying is OK in MongoDB ... 'one fact one place' doesn't apply here ... provided you have some way to update the copy when the main one changes (eventual consistency).
BTW, on DBRef's, the official guidance says "Most developers only use DBRefs if the collection can change from one document to the next. If your referenced collection will always be the same, the manual references outlined above are more efficient."
Also, why do you want to reference info within a document? If it was an array I could understand why you might want to refer to individual entries but since it doesn't appear to be an array in your example, why not just refer to the containing document by its _id?