MongoDB: Insert does not modify a list of documents? - list

Question

Adding new value in a list with insert completes ok but document remains unmodified:
> graph = {graph:[
... {_id:1, links: [2,3,4]},
... {_id:2, links: [5,6]},
... {_id:3, links: [7]},
... {_id:4, links: [9,10]}
... ]}
{
"graph" : [
{
"_id" : 1,
"links" : [
2,
3,
4
]
},
{
"_id" : 2,
"links" : [
5,
6
]
},
{
"_id" : 3,
"links" : [
7
]
},
{
"_id" : 4,
"links" : [
9,
10
]
}
]
}
> db.test.insert(graph)
WriteResult({ "nInserted" : 1 })
> db.runCommand(
... {
... insert: "graph",
... documents: [ {_id:5, links: [1,8]} ]
... }
... )
{ "ok" : 1, "n" : 1 }
Yet getting elements after insert does not have a new inserted element:
> db.test.find()
{ "_id" : ObjectId("538c8586562938c6afce9924"), "graph" : [
{ "_id" : 1, "links" : [ 2, 3, 4 ] },
{ "_id" : 2, "links" : [ 5, 6 ] },
{ "_id" : 3, "links" : [ 7 ] },
{ "_id" : 4, "links" : [ 9, 10 ] } ] }
>
What's wrong?
Update
> db.test.find()
{ "_id" : ObjectId("538c8586562938c6afce9924"), "graph" : [ { "_id" : 1, "links" : [ 2, 3, 4 ] }, { "_id" : 2, "links" : [ 5, 6 ] }, { "_id" : 3, "links" : [ 7 ] }, { "_id" : 4, "links" : [ 9, 10 ] } ] }
>
db.test.update(
{_id : 538c8586562938c6afce9924},
{$push : {
graph : {{_id:5, links: [1,8]}}
}
}
);
2014-06-03T12:35:11.695+0400 SyntaxError: Unexpected token {

Answer 1

You have to update the collection. Using db.runCommand() is not exactly the right way. It is essentially used for working in the context of database for performing tasks that extend to authentication, user management, role management and replication etc. The complete usability of db.runCommand() can be seen in MongoDB docs here.
The simplest way is using the update on collection. One of the reason why this query may not work for you is not supplying the _id to MongoDB in proper way.
_id : "ObjectId("538dcfaf8f00ec71aa055b15")" or _id : "538dcfaf8f00ec71aa055b15" are not same as _id : ObjectId("538dcfaf8f00ec71aa055b15") for MongoDB. The first and second ones are string type while the last one is an ObjectId type.
db.test.update(
{_id : ObjectId("538dcfaf8f00ec71aa055b15")}, //i.e. query for finding the doc to update
{$push : {
graph : {{_id:5, links: [1,8]}}
}
}, //performing the update
{} //optional parameters
);
But if you insist on using db.runCommand() then to get this same thing done you will need to write it as follows:
db.runCommand ({
update: 'Test',
updates:
[
{
q: {_id : ObjectId("538dcfaf8f00ec71aa055b15")},
u: {$push : {'graph' : {_id:5, links: [1,8]}}}
}
]
});
What you have done is inserting something in a "graph" collection! You can do a show collections on your db and you will find that as a result of your incorrect db.runCommand(...) you ended up creating a new collection.
Hope it helped.