I have a collection like the one below
I need to push a new object into the "stores" array using extended json.
How can I instruct the Mongodb to create a new ObjectId for the attribute _id ?
I'm wondering something like this:
{
'_id' : { '$oid' : '$<here_some_command_to_generate_new_oid_automatically>' },
'address' : 'my store address',
'contact' : 'John Doe'
}
The solution is specify like this in the json "id":{"$oid": "<ObjectId()>"},
Unless I misunderstood you ,if you just need to generate using client side you can do it the same way any driver would do for top level documents.
In java to generate extended json version you could use JsonWriterSettings with output mode as JsonMode.Extended. Something like
JsonWriterSettings setting = JsonWriterSettings.builder().outputMode(JsonMode.EXTENDED).build();
Document id = new Document("_id", new ObjectId());
String extendedIdJson = id.toJson(setting);// {'_id' : { '$oid' : '507f191e810c19729de860ea' }}
Related
I have a document like below:
"application" : "test",
"QA1" : {
"url" : "https://google.co.in",
"db" : {
"userName" : "user",
"password" : "pswd"
}
}
I want to retrieve the value "https://google.co.in" by calling the key "url".
While using the below shell command, I am able to retrieve the value as expected.
db.getCollection('Application_Data').findOne({"application":"test"}).QA1.url
But when I convert it to java code, it is throwing me null pointer exception:
cursor = collection.find(Filters.eq("application","test")).iterator();
while (cursor.hasNext()) {
value=cursor.next().get("QA1.url").toString();
break;
}
I also tried with projection like below to get the required values:
cursor = collection.find(Filters.and(Filters.eq("application","test"))).projection(Projections.fields(Projections.include("QA1.url"),Projections.excludeId())).iterator();
while (cursor.hasNext()) {
System.out.println(cursor.next().get("QA1").toString());
}
This is giving me the output as below:
Document{{url=https://google.co.in}}
It is still not giving me the exact value. Appreciate your help on this.
Mongodb Documents are nested. So say, in your example, when you do cursor.next().get("QA1"), you get the Document under "QA1" property.
So the way to achieve what you want is
cursor.next().get("QA1").get("url"). That, with proper error handling (think exceptions).
A better way to do what you want is to use a mapper like spring-data-mongodb that would map the JSON response of mongodb into a java object for you automatically.
You need to use the Document class's getEmbedded method to extract the nested field's value.
while (cursor.hasNext()) {
Document doc = cursor.next();
System.out.println(doc.toJson());
String urlValue = doc.getEmbedded(Arrays.asList("QA1","url"), String.class);
System.out.println(urlValue); // output below
}
The result is as expected - a string: https://google.co.in
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")});
I have these documents stored in my mongoDB database.
{
'_id' : 1,
'field1' : {
'cool_field1': 'value_1',
'name' : 'good_name'
}
'field2' : {
'cool_field1': 'value_2',
'name' : 'bad_name'
}
}
I'd like to query on 'name': 'good_name' and I'd like to get field1. Since I do not know in which nested document good_name will be present, I can't use path query. I do not know if Mongo has a way of solving my problem or I will have to iterate over the full document in my native language once I retrieved the document.
Thanks.
Mongo wildcard query has been a long outstanding issue that you can track here. Apparently no immediate out of the box solution to do this on the server.
I'm having a little trouble writing a query that needs to compare a given value against a certain field in all embedded documents within an array. I will give an example to make the issue less abstract.
Let's say I want to use MongoDB to store the last queries that users on my network have entered into different online search engines. An entry in the collection would have a structure like this :
{
'_id' : 'zinfandel',
'last_search' : [
{
'engine' : 'google.com',
'query' : 'why is the sky blue'
},
{
'engine' : 'bing.com',
'query' : 'what is love'
},
{ 'engine' : 'yahoo.com',
'query' : 'how to tie a tie'
}
]
}
Now let's say user username enters a new query into a certain engine. The code that stores this query in the DB needs to find out whether there already exists an entry for the engine that the user used. If yes, this entry is to be updated with the new query. If not, a new entry should be created. My idea is to do a $push only if there is no entry for the given engine and do a $set otherwise. For this purpose, I tried to write my push like this :
db.mycollection.update(
{ '_id' : username , search.$.engine : { '$ne' : engine } },
{ '$push' : { 'search.$.engine' : engine, 'search.$.query' : query } }
)
However, this pushes a new embedded document even if there already was an entry for the given engine. The problem seems to be that the $ne operator doesn't work with arrays like I expect it to work. What I need is a way to make sure that not a single embedded document in the array has an "engine" entry that matches the specified engine.
Does anyone have an idea how to do that? Please tell me if I need to further clarify the question ...
You can push the item into the array with the following command:
db.mycollection.update({
_id: "zinfandel",
"last_search.engine": {
$nin: ["notwellknownengine.com"]
}
}, {
$push: {
"last_search": {
"engine" : "notwellknownengine.com",
"query" : "stackoveflow.com"
}
}
});
I have recently changed one of my fields from object to array of objects.
In my production I have only 14 documents with this field, so I decided to change those fields.
Is there any best practices to do that?
As it is in my production I need to do it in a best way possible?
I got the document Id's of those collections.like ['xxx','yyy','zzz',...........]
my doc structure is like
_id:"xxx",option1:{"op1":"value1","op2":"value2"},option2:"some value"
and I want to change it like(converting object to array of objects)
_id:"xxx",option1:[{"op1":"value1","op2":"value2"},
{"op1":"value1","op2":"value2"}
],option2:"some value"
Can I use upsert? If so How to do it?
Since you need to create the new value of the field based on the old value, you should retrieve each document with a query like
db.collection.find({ "_id" : { "in" : [<array of _id's>] } })
then iterate over the results and $set the value of the field to its new value:
db.collection.find({ "_id" : { "in" : [<array of _id's>] } }).forEach(function(doc) {
oldVal = doc.option1
newVal = compute_newVal_from_oldVal(oldVal)
db.collection.update({ "_id" : doc._id }, { "$set" : { "option" : newVal } })
})
The document structure is rather schematic, so I omitted putting in actual code to create newVal from oldVal.
Since it is an embedded document type you could use push query
db.collectionname.update({_id:"xxx"},{$push:{option1:{"op1":"value1","op2":"value2"}}})
This will create document inside embedded document.Hope it helps