I'm new to meteor/mongo/js as a stack and I'm getting lost in JSON arrays and referencing them. Based another SO answer ( and the docs) I think I am close...
A document in the Orders collection, the document has nested arrays.
Order -> orderLines -> lineItems:
Sample doc:
{
"_id" : "27tGpRtMWYqPpFkDN",
"orderLines" : [
{
"lineId" : 1,
"name" : "Cheese & Pickle",
"instructions" : "",
"lineItems" : [
{
"name" : "Cheddar Cheese",
"quantity" : 1
},
{
"name" : "Branston Pickle",
"quantity" : 1
},
{
"name" : "Focaccia Roll",
"quantity" : 1
}
]
}
]
}
What I'm trying to do from the meteor/mongo shell:
Add "instructions" of "foo" to orderLines where lineId = 1
Put a new item on lineItems array
This appears to hang...
meteor:PRIMARY> db.orders.update({_id:"27tGpRtMWYqPpFkDN","orderLines.lineId":"1", {$set: {"orderLines.$.instructions":"foo"}})
...
This doesn't like the identifier in the query
meteor:PRIMARY> db.orders.update({_id:"27tGpRtMWYqPpFkDN", "orderLines.lineId":"1"}, {$push:{"orderLines.$.lineItems":" { "name" : "butter", "quantity" : 1}"}});
2015-10-27T16:09:54.489+0100 SyntaxError: Unexpected identifier
Thanks all for your comments... but I found out some answers, posted for reference
Item 1 - using $set on a value within an array
This was failing due to two typos, one missing closing } at the end of the query, second was quoting the value "1" for itemId in the query.
This works:
db.orders.update({_id:"27tGpRtMWYqPpFkDN", orderLines.lineId":1},
{$set: {"orderLines.$.instructions":"foo"}})
I also realised that when I said "It appears to hang" it is the cli waiting for a valid statement, so hints at a missing } or )!
Item 2 - using $push to add data to an array - 2 levels nested
This was failing due to quoting around the array data
db.orders.update({_id:"27tGpRtMWYqPpFkDN", "orderLines.lineId":1 },
{$push:{"orderLines.$.lineItems": { "name" : "butter", "quantity" : 1} }})
Nested Arrays: can use $ positional operator
What I want to do next is use $set on an item in the second level array, and this would require using the $ positional operator twice:
db.orders.update({"orderLines.lineId":1, lineItems.name:"Cheddar Cheese"},
{$set: {"orderLines.$.lineItems.$.quantity": 2}})
This throws an error:
Too many positional (i.e. '$') elements found in path
There is an open MongoDB enhancement request for this but it's been open since 2010
$push adds a new element to an array. You're merely trying to set the value of a particular key in an array element.
Try:
db.orders.update({ _id: "27tGpRtMWYqPpFkDN", "orderLines.lineId": 1},
{ $set: { "orderlines.$.instructions": "foo" }})
docs
Related
I've got collection with volunteer information in it, and it lists the volunteers as an array of objects. I can display all the shifts for each volunteer, but removing one from the array is proving difficult for me:
Sample data:
"_id" : ObjectId("59180305c19dbaa4ecd9ee59"),
"where" : "Merchandise tent",
"description" : "Sell gear at the merchandise tent.",
"shifts" : [
{
"dateNeeded" : ISODate("2017-06-23T00:00:00Z"),
"timeslot" : "8:00 - NOON",
"needed" : 2,
"_id" : ObjectId("591807546a71c3a57d1a2105"),
"volunteers" : [
{
"fullname" : "Mary Mack",
"phone" : "1234567890",
"email" : "mary#gmail.com",
"_id" : ObjectId("591ce45bc7e8a8c7b742474c")
}
]
},
The data I have available for this is:
_id, where, shifts.timeslot, shifts.dateNeeded, volunteers.email
Can someone help me? Lets say Mary Mack wants to unVolunteer for the 8 - Noon shift at the merchandise tent. She may be listed under other shifts as well, but we only want to remove her from this shift.
You can do this by specifying something to match the "document" and then the required "shifts" array entry as the query expression for an .update(). Then apply the positional $ operator for the matched array index with $pull:
db.collection.update(
{ "_id": ObjectId("59180305c19dbaa4ecd9ee59"), "shifts.timeslot": "8:00 - NOON" },
{ "$pull": { "shifts.$.volunteers": { "fullname": "Mary Mack" } } }
)
That is okay in this instance since you are only trying to "match" on the "outer" array in the nested structure and the $pull has query arguments of it's own to identify the array entry to remove.
You really should be careful using "nested arrays" though. As whilst a $pull operation like this works, updates to the "inner" array are not really possible since the positional $ operator will only match the "first" element that meets the condition. So your example of "Mary Mack" in multiple shifts would only ever match in the first "shifts" array entry found.
Try this
db.example.update(
{},
{ $unset: {"Mary Mack":1}},
false, true
)
Im trying to get back into Mongodb and Ive come across something that I cant figure out.
I have this data structure
> db.ratings.find().pretty()
{
"_id" : ObjectId("55881e43424cbb1817137b33"),
"e_id" : ObjectId("5565e106cd7a763b2732ad7c"),
"type" : "like",
"time" : 1434984003156,
"u_id" : ObjectId("55817c072e48b4b60cf366a7")
}
{
"_id" : ObjectId("55893be1e6a796c0198e65d3"),
"e_id" : ObjectId("5565e106cd7a763b2732ad7c"),
"type" : "dislike",
"time" : 1435057121808,
"u_id" : ObjectId("55817c072e48b4b60cf366a7")
}
{
"_id" : ObjectId("55893c21e6a796c0198e65d4"),
"e_id" : ObjectId("5565e106cd7a763b2732ad7c"),
"type" : "null",
"time" : 1435057185089,
"u_id" : ObjectId("55817c072e48b4b60cf366a7")
}
What I want to be able to do is count the documents that have either a like or dislike leaving the "null" out of the count. So I should have a count of 2. I tried to go about it like this whereby I set the query to both fields:
db.ratings.find({e_id: ObjectId("5565e106cd7a763b2732ad7c")}, {type: "like", type: "dislike"})
But this just prints out all three documents. Is there any reason?
If its glaringly obvious im sorry pulling out my hair at the moment.
Use the following db.collection.count() method which returns the count of documents that would match a find() query:
db.ratings.count({
"e_id": ObjectId("5565e106cd7a763b2732ad7c"),
type: {
"$in": ["like", "dislike"]
}
})
The db.collection.count() method is equivalent to the db.collection.find(query).count() construct. Your query selection criteria above can be interpreted as:
Get me the count of all documents which have the e_id field values as ObjectId("5565e106cd7a763b2732ad7c") AND the type field which has either value "like" or "dislike", as depicted by the $in operator that selects the documents where the value of a field equals any value in the specified array.
db.ratings.find({e_id: ObjectId("5565e106cd7a763b2732ad7c")},
{type: "like", type: "dislike"})
But this just prints out all three
documents. Is there any reason? If its glaringly obvious im sorry
pulling out my hair at the moment.
The second argument here is the projection used by the find method . It specifies fields that should be included -- regardless of their value. Normally, you specify a boolean value of 1 or true to include the field. Obviously, MongoDB accepts other values as true.
If you only need to count documents, you should issue a count command:
> db.runCommand({count: 'collection',
query: { "e_id" : ObjectId("5565e106cd7a763b2732ad7c"),
type: { $in: ["like", "dislike"]}}
})
{ "n" : 2, "ok" : 1 }
Please note the Mongo Shell provides the count helper for that:
> db.collection.find({ "e_id" : ObjectId("5565e106cd7a763b2732ad7c"),
type: { $in: ["like", "dislike"]}}).count()
2
That being said, to quote the documentation, using the count command "can result in an inaccurate count if orphaned documents exist or if a chunk migration is in progress." To avoid that, you might prefer using the aggregation framework:
> db.collection.aggregate([
{ $match: { "e_id" : ObjectId("5565e106cd7a763b2732ad7c"),
type: { $in: ["like", "dislike"]}}},
{ $group: { _id: null, n: { $sum: 1 }}}
])
{ "_id" : null, "n" : 2 }
This query should solve your problem
db.ratings.find({$or : [{"type": "like"}, {"type": "dislike"}]}).count()
Aggregate, $unwind and $group is not my solution as they make query very slow, there for I am looking to get my record by db.collection.find() method.
The problem is that I need more then one value from sub array. For example from the following example I want to get the "type" : "exam" and "type" : "quiz" elements.
{
"_id" : 22,
"scores" : [
{
"type" : "exam",
"score" : 75.04996547553947
},
{
"type" : "quiz",
"score" : 10.23046475899236
},
{
"type" : "homework",
"score" : 96.72520512117761
},
{
"type" : "homework",
"score" : 6.488940333376703
}
]
}
I am looking something like
db.students.find(
// Search criteria
{ '_id': 22 },
// Projection
{ _id: 1, scores: { $elemMatch: { type: 'exam', type: 'quiz' } }}
)
The result should be like
{ "_id": 22, "scores" : [ { "type" : "exam", "type" : "quiz" } ] }
But this over ride the type: 'exam' and returns only type: 'quiz'. Have anybody any idea how to do this with db.find()?
This is not possible directly using find and elemMatch because of following limitation of elemMatch and mongo array fields.
The $elemMatch operator limits the contents of an field from the query results to contain only the first element matching the $elemMatch condition. ref. from $elemMacth
and mongo array field limitations as below
Only one positional $ operator may appear in the projection document.
The query document should only contain a single condition on the array field being projected. Multiple conditions may override each other internally and lead to undefined behavior. ref from mongo array field limitations
So either you tried following this to find out only exam or quiz
db.collectionName.find({"_id":22,"scores":{"$elemMatch":{"type":"exam"}}},{"scores.$.type":1}).pretty()
is shows only exam scores array.
Otherwise you should go through aggregation
db.aaa.insert({"_id":1, "m":[{"_id":1,"a":1},{"_id":2,"a":2}]})
db.aaa.find({"_id":1,"m":{$elemMatch:{"_id":1}}})
{ "_id" : 1, "m" : [ { "_id" : 1, "a" : 1 }, { "_id" : 2, "a" : 2 } ] }
Using $elemMatch as query operator, it return all sub docs in 'm' !! Strange!
Use it as project operator:
db.aaa.find({"_id":1},{"m":{$elemMatch:{"_id":1}}})
{ "_id" : 1, "m" : [ { "_id" : 1, "a" : 1 } ] }
This is OK. Following this logic, use it as query operator in update will change all sub docs in 'm'. So I do:
db.aaa.update({"_id":1,"m":{$elemMatch:{"_id":1}}},{$set:{"m.$.a":3}})
db.aaa.find()
{ "_id" : 1, "m" : [ { "_id" : 1, "a" : 3 }, { "_id" : 2, "a" : 2 } ] }
It works in manner of as second example(project operator). This really confuse me.
Give me a explain
It Isn't strange, it's how it works.
You are using $elemMatch to match an element within an array contained in your document. That means it mactches the "document" and not the "array element", so it does not just selectively display only the array element that was matched.
What you can do, and how you used it in with the $set operator, is use a positional $ operator to indicate the matched "position" from your query side:
db.aaa.find({"_id":1},{"m":{$elemMatch:{"_id":1}}},{ "m.$": 1 })
And that will show you only one element of the array. But it is of course *still an array in the result shown, and you cannot cast it to a different type.
The other part of the usage is that this will only match once. And only the first match will be assigned to the positional operator.
So perhaps the most succinct explaination is you matching the "document that contains" the properties of the sub-document your specified in your query, and not just the "sub-document" itself.
See the documentation for more:
http://docs.mongodb.org/manual/reference/operator/projection/positional/
http://docs.mongodb.org/manual/reference/operator/query/elemMatch/
I have a DB structure like below:
{
"_id" : 1,
"comments" : [
{
"_id" : 2,
"content" : "xxx"
}
]
}
I update a new subdocument in the comments feild. It is OK.
db.test.update(
{"_id" : 1, "comments._id" : 2},
{$push : {"comments.$.comments" : {_id : 3, content:"xxx"}}}
)
after that the DB structure:
{
"_id" : 1,
"comments" : [
{
"_id" : 2,
"comments" : [
{
"id" : 3,
"content" : "xxx"
}
],
"content" : "xxx"
}
]
}
But when I update a new subdocument in the comment field that _id is 3, There is a error:
db.test.update(
{"_id" : 1, "comments.comments.id" : 3},
{$push : {"comments.comments.$.comments" : {id : 4, content:"xxx"}}}
)
error message:
can't append to array using string field name: comments
Well, it makes total sense if you think about it. MongoDb has the advantage and the disadvantage of solving magically certain things.
When you query the database for a specific regular field like this:
{ field : "value" }
The query {field:"value"} makes total sense, it wouldn't in case value is part of an array but Mongo solves it for you, so in case the structure is:
{ field : ["value", "anothervalue"] }
Mongo iterates through all of them and matches "value" into the field and you don't have to think about it. It works perfectly.. at only one level, because it's impossible to guess what you want to do if you have multiple levels
In your case the first query works because it's the case in this example:
db.test.update(
{"_id" : 1, "comments._id" : 2},
{$push : {"comments.$.comments" : {_id : 3, content:"xxx"}}}
)
Matches _id in the first level, and comments._id at the second level, it gets an array as a result but Mongo is able to solve it.
But in the second case, think what you need, let's isolate the where clause:
{"_id" : 1, "comments.comments.id" : 3},
"Give me from the main collection records with _id:1" (one doc)
"And comments which comments inside have and id=3" (array * array)
The first level is solved easily, comments.id, the second is not possible due comments returns an array, but one more level is an array of arrays and Mongo gets an array of arrays as a result and it's not possible to push a document into all the records of the array.
The solution is to narrow your where clause to obtain an unique document in comments (could be the first one) but it's not a good solution because you never know what is the position of the document you're looking for, using the shell I think the only option to be accurate is to do it in two steps. Check this query that works (not the solution anyway) but "solves" the multiple array part fixing it to the first record:
db.test.update(
{"_id" : 1, "comments.0.comments._id" : 3},
{$push : {"comments.0.comments.$.comments" : {id : 4, content:"xxx"}}}
)