I would like to know how can we access nested array elements in MongoDB
For example, if we have something like :
{
array1 : [
{
array11 : {
name11 : "xyz"
}
},{
array12 : {
name12: "abc",
nums : [1,2,3,4]
}
}
]
}
Now how can I access and update the "name12" field.
And how can I add elements to "nums" field.
A) To find the collection : I am assuming you want to find name12 = "abc".
db.mydata.find({"array1.array12.name12":"abc"}).pretty()
B) To update & Add elements to the nums array use the positional operator :
https://docs.mongodb.com/manual/reference/operator/update/positional/
db.mydata.update({"array1.array12.name12":"abc"},
{$set:{"array1.$.name12":"abc"} ,
$push:{"array1.$.nums":5}
})
On a side note, you should consider redefining your schema so that the arrays have similar structures. It will help you to update in the long run..
you can access it like any traditional js array, in this case, youre accessing objects within arrays so take care of the syntax.
Related
I have a database collection where each row has a unique ID associated with it. I want to be able to query my database and match data from it with the IDs in each of the objects from an array. The _ids are a string.
Collection Example:
"_id" : "453241",
"name" : "Item1",
"_id" : "621984",
"title" : "Item2",
"_id" : "832127",
"title" : "Item3",
The object would look something like this:
query = [{"_id":"621984","quantity":"3"},{"_id":"832127","quantity":"2"}]
The desired output would be something like this (I do not want to write to the database the quantity):
output = [{"_id":"621984","Item2", "quantity":"3"},{"_id":"832127", "Item3" ,"quantity":"2"}]
From the other threads, I read from what I understand we have to use the $is to match the data. Like the one in this example MongoDB select where in array of _id? However, the issue with this is that they are using an array of IDs. And I'm not sure how we would append the quantity to this value.
I also considered iterating through a loop of all of the objects inside of the array and then searching the database. And appending the output to an array. This would be most beneficial as I would want the overall output to include the quantity as well.
console.logging result in this case works and outputs the designated ID table however when attempting to append the values to output and then returning this does not work and returns an empty array.
output = []
for (item in query) {
collection.find({"id": item._id}).then((result) => { output.push(result + item.quantity) })
}
return output
Any ideas or help would be greatly appreciated thanks.
I've run into very similar situations with my own implementations as far as efficiency is concerned. The approach that I ended up taking (granted in a one-to-many relationship) is the following.
Isolate the Ids into an array prior to the Mongoose Query
let ids = []
for (object in query) {
ids.push(query[object]._id)
}
collection.find({ id : $in : ids }).then((result) => {
for (let i in result) {
for (let j in query) {
if (result[i]._id === query[j]._id) {
query[j].name = result[i].name
}
}
}
}).catch((error) => {
console.log("Query Error")
})
Also, in the above example, taking the array of Ids is going to require the Mongo $in operator to search through the array and return the appropriate collection items.
I hope this helps!
I have a collection of product in which I have document like this
"_id" : ObjectId("5acb1dad698eaa7a254c9017"),
"txtProductCode" : "1233A",
"txtModelCode" : "00M",
"txtPartNo" : "00P",
"txtSerialNo" : "00S",
"txtProductName" : "Watch",
"traderId" : ObjectId("5ac5fb29b0f9b3444e6c1ef2")
I want to search a product based on its name and traderId for which I used
db.getCollection('product').find( {$and:[{'txtProductName':"Watch"},{"traderId" : ObjectId("5ac5fb29b0f9b3444e6c1ef2")}]})
its working fine but now if a user have input model no then it shoud use model number also to search for a product if the user have not input the model no then it should without model number
So My question is do I have to use cases like this
if(req.body.modelNo)
db.getCollection('product').find( {$and:[{'txtProductName':"Watch"},{"traderId" : ObjectId("5ac5fb29b0f9b3444e6c1ef2")},{'txtModelCode':"00M"}]})
else
db.getCollection('product').find( {$and:[{'txtProductName':"Watch"},{"traderId" : ObjectId("5ac5fb29b0f9b3444e6c1ef2")}]})
or is there a way to do this without making cases I have to do this for multiple condtions so I am trying not to use cases
Create the query object first then add the extra key with a conditional check. No need to explicitly use the $and operator when specifying a comma separated list of expressions as it's implicitly provided:
let query = {
'txtProductName': 'Watch',
'traderId': ObjectId('5ac5fb29b0f9b3444e6c1ef2')
};
if (req.body.modelNo) query['txtModelCode'] = req.body.modelNo;
db.getCollection('product').find(query);
If using the $and operator, you can push the additional query into an array then use the list for the $and operator:
let andOperator = [
{ 'txtProductName': 'Watch' },
{ 'traderId': ObjectId('5ac5fb29b0f9b3444e6c1ef2') }
];
if (req.body.modelNo) andOperator.push({ 'txtModelCode': req.body.modelNo });
// if (req.body.modelNo) andOperator = [...andOperator, { 'txtModelCode': req.body.modelNo }];
db.getCollection('product').find({ '$and': andOperator });
Well, I would have done this in this way
First, you should send a json of specific from to backend. for example
[{'txtModelCode':"00M"},{'txtPartNo':"AC"},{'Yts':"xyz"}]
OR
[{'txtModelCode':"00M"},{'txtPartNo':"AC"}]
OR
[{'txtModelCode':"00M"}]
This is the payload that you should expect in req.body. And finally you can use it in your find() criteria. Something like
db.getCollection('product').find( {$and:[{'txtProductName':"Watch"},
{"traderId" : ObjectId("5ac5fb29b0f9b3444e6c1ef2")}, ...req.body]})
... is called spread operator. Spread syntax allows an iterable such as an array expression or string to be expanded. Read more about it here
This will make it totally dynamic. Any scaling in collection can directly be used in find criteria. you never have to add extra line of code
This is the case: A webshop in which I want to configure which items should be listed in the sjop based on a set of parameters.
I want this to be configurable, because that allows me to experiment with different parameters also change their values easily.
I have a Product collection that I want to query based on multiple parameters.
A couple of these are found here:
within product:
"delivery" : {
"maximum_delivery_days" : 30,
"average_delivery_days" : 10,
"source" : 1,
"filling_rate" : 85,
"stock" : 0
}
but also other parameters exist.
An example of such query to decide whether or not to include a product could be:
"$or" : [
{
"delivery.stock" : 1
},
{
"$or" : [
{
"$and" : [
{
"delivery.maximum_delivery_days" : {
"$lt" : 60
}
},
{
"delivery.filling_rate" : {
"$gt" : 90
}
}
]
},
{
"$and" : [
{
"delivery.maximum_delivery_days" : {
"$lt" : 40
}
},
{
"delivery.filling_rate" : {
"$gt" : 80
}
}
]
},
{
"$and" : [
{
"delivery.delivery_days" : {
"$lt" : 25
}
},
{
"delivery.filling_rate" : {
"$gt" : 70
}
}
]
}
]
}
]
Now to make this configurable, I need to be able to handle boolean logic, parameters and values.
So, I got the idea, since such query itself is JSON, to store it in Mongo and have my Java app retrieve it.
Next thing is using it in the filter (e.g. find, or whatever) and work on the corresponding selection of products.
The advantage of this approach is that I can actually analyse the data and the effectiveness of the query outside of my program.
I would store it by name in the database. E.g.
{
"name": "query1",
"query": { the thing printed above starting with "$or"... }
}
using:
db.queries.insert({
"name" : "query1",
"query": { the thing printed above starting with "$or"... }
})
Which results in:
2016-03-27T14:43:37.265+0200 E QUERY Error: field names cannot start with $ [$or]
at Error (<anonymous>)
at DBCollection._validateForStorage (src/mongo/shell/collection.js:161:19)
at DBCollection._validateForStorage (src/mongo/shell/collection.js:165:18)
at insert (src/mongo/shell/bulk_api.js:646:20)
at DBCollection.insert (src/mongo/shell/collection.js:243:18)
at (shell):1:12 at src/mongo/shell/collection.js:161
But I CAN STORE it using Robomongo, but not always. Obviously I am doing something wrong. But I have NO IDEA what it is.
If it fails, and I create a brand new collection and try again, it succeeds. Weird stuff that goes beyond what I can comprehend.
But when I try updating values in the "query", changes are not going through. Never. Not even sometimes.
I can however create a new object and discard the previous one. So, the workaround is there.
db.queries.update(
{"name": "query1"},
{"$set": {
... update goes here ...
}
}
)
doing this results in:
WriteResult({
"nMatched" : 0,
"nUpserted" : 0,
"nModified" : 0,
"writeError" : {
"code" : 52,
"errmsg" : "The dollar ($) prefixed field '$or' in 'action.$or' is not valid for storage."
}
})
seems pretty close to the other message above.
Needles to say, I am pretty clueless about what is going on here, so I hope some of the wizzards here are able to shed some light on the matter
I think the error message contains the important info you need to consider:
QUERY Error: field names cannot start with $
Since you are trying to store a query (or part of one) in a document, you'll end up with attribute names that contain mongo operator keywords (such as $or, $ne, $gt). The mongo documentation actually references this exact scenario - emphasis added
Field names cannot contain dots (i.e. .) or null characters, and they must not start with a dollar sign (i.e. $)...
I wouldn't trust 3rd party applications such as Robomongo in these instances. I suggest debugging/testing this issue directly in the mongo shell.
My suggestion would be to store an escaped version of the query in your document as to not interfere with reserved operator keywords. You can use the available JSON.stringify(my_obj); to encode your partial query into a string and then parse/decode it when you choose to retrieve it later on: JSON.parse(escaped_query_string_from_db)
Your approach of storing the query as a JSON object in MongoDB is not viable.
You could potentially store your query logic and fields in MongoDB, but you have to have an external app build the query with the proper MongoDB syntax.
MongoDB queries contain operators, and some of those have special characters in them.
There are rules for mongoDB filed names. These rules do not allow for special characters.
Look here: https://docs.mongodb.org/manual/reference/limits/#Restrictions-on-Field-Names
The probable reason you can sometimes successfully create the doc using Robomongo is because Robomongo is transforming your query into a string and properly escaping the special characters as it sends it to MongoDB.
This also explains why your attempt to update them never works. You tried to create a document, but instead created something that is a string object, so your update conditions are probably not retrieving any docs.
I see two problems with your approach.
In following query
db.queries.insert({
"name" : "query1",
"query": { the thing printed above starting with "$or"... }
})
a valid JSON expects key, value pair. here in "query" you are storing an object without a key. You have two options. either store query as text or create another key inside curly braces.
Second problem is, you are storing query values without wrapping in quotes. All string values must be wrapped in quotes.
so your final document should appear as
db.queries.insert({
"name" : "query1",
"query": 'the thing printed above starting with "$or"... '
})
Now try, it should work.
Obviously my attempt to store a query in mongo the way I did was foolish as became clear from the answers from both #bigdatakid and #lix. So what I finally did was this: I altered the naming of the fields to comply to the mongo requirements.
E.g. instead of $or I used _$or etc. and instead of using a . inside the name I used a #. Both of which I am replacing in my Java code.
This way I can still easily try and test the queries outside of my program. In my Java program I just change the names and use the query. Using just 2 lines of code. It simply works now. Thanks guys for the suggestions you made.
String documentAsString = query.toJson().replaceAll("_\\$", "\\$").replaceAll("#", ".");
Object q = JSON.parse(documentAsString);
If i have two collections where one of that have dbref, how is possibile to join using $lookup and dbref?
DBref is a BSON Object and you cannot make a lookup using its value.
BUT, there is a way to do it, transforming a DBRef object into an array.
I have written an answer a few months ago describing how to do it.
Short explanation
Say you have DBRef object like this :
myField: DBRef("otherCollection", ObjectId("582abcd85d2dfa67f44127e0")),
Use $objectToArray on myField like this
db.myColl.aggregate([
{
$project: {
transformedDBRef: {$objectToArray: "$myField"},
}
},
])
The result would be an array of two objects, one object for the reference, one for the ObjectId contained within the DBRef, each with a field "k" and a field "v". It will look like this:
transformedDBRef: [{"k" : "$ref","v" : "otherCollection"},{"k" : "$id","v" : ObjectId("582abcd85d2dfa67f44127e0")}
You can then grep the ObjectId. For the complete solution, please check the link above.
I Want to query CouchDB and I have a specific need : my query should return the name field of documents corresponding to this condition : the id is equal or contained in a document filed (a list).
For example, the field output is the following :
"output": [
"doc_s100",
"doc_s101",
"doc_s102",
"doc_s103",
],
I want to get all the documents having in their output field "doc_s102" for example.
I wrote a view in a design document :
"backward_by_docid": {
"map": "function(doc) {if(doc.output) emit(doc.output, doc.name)}"
}
but this view works only when I have a unique value in the output field.
How can I resolve this query ?
Thanks !
you have to iterate over the array:
if(doc.output) {
for (var curOutput in doc.output) {
emit (doc.output[curOutput],doc.name);
}
}
make sure that output always is an array (at least [])
.. and, of course use key="xx" instead key=["xxx"]