Is it possible to create a partial index on a collection using the array operator $size? For example, if I had a blogPost schema with an array field comments:[type:String], could I index the collection based on the number of comments per blogPost
I don't believe you can index by array length. However you can modify your schema to have a comment count. You can then add an index on that field and use atomic update operations to add comments while incrementing the comment count:
BlogPost.update(
{
_id: "123"
},
{
$push: {
comments: "new comment"
},
$inc: {
commentCount: 1
}
}, callback);
Just add an index on commentCount and it should solve your problem.
Related
I am trying to update a value in the nested array but can't get it to work.
My object is like this
{
"_id": {
"$oid": "1"
},
"array1": [
{
"_id": "12",
"array2": [
{
"_id": "123",
"answeredBy": [], // need to push "success"
},
{
"_id": "124",
"answeredBy": [],
}
],
}
]
}
I need to push a value to "answeredBy" array.
In the below example, I tried pushing "success" string to the "answeredBy" array of the "123 _id" object but it does not work.
callback = function(err,value){
if(err){
res.send(err);
}else{
res.send(value);
}
};
conditions = {
"_id": 1,
"array1._id": 12,
"array2._id": 123
};
updates = {
$push: {
"array2.$.answeredBy": "success"
}
};
options = {
upsert: true
};
Model.update(conditions, updates, options, callback);
I found this link, but its answer only says I should use object like structure instead of array's. This cannot be applied in my situation. I really need my object to be nested in arrays
It would be great if you can help me out here. I've been spending hours to figure this out.
Thank you in advance!
General Scope and Explanation
There are a few things wrong with what you are doing here. Firstly your query conditions. You are referring to several _id values where you should not need to, and at least one of which is not on the top level.
In order to get into a "nested" value and also presuming that _id value is unique and would not appear in any other document, you query form should be like this:
Model.update(
{ "array1.array2._id": "123" },
{ "$push": { "array1.0.array2.$.answeredBy": "success" } },
function(err,numAffected) {
// something with the result in here
}
);
Now that would actually work, but really it is only a fluke that it does as there are very good reasons why it should not work for you.
The important reading is in the official documentation for the positional $ operator under the subject of "Nested Arrays". What this says is:
The positional $ operator cannot be used for queries which traverse more than one array, such as queries that traverse arrays nested within other arrays, because the replacement for the $ placeholder is a single value
Specifically what that means is the element that will be matched and returned in the positional placeholder is the value of the index from the first matching array. This means in your case the matching index on the "top" level array.
So if you look at the query notation as shown, we have "hardcoded" the first ( or 0 index ) position in the top level array, and it just so happens that the matching element within "array2" is also the zero index entry.
To demonstrate this you can change the matching _id value to "124" and the result will $push an new entry onto the element with _id "123" as they are both in the zero index entry of "array1" and that is the value returned to the placeholder.
So that is the general problem with nesting arrays. You could remove one of the levels and you would still be able to $push to the correct element in your "top" array, but there would still be multiple levels.
Try to avoid nesting arrays as you will run into update problems as is shown.
The general case is to "flatten" the things you "think" are "levels" and actually make theses "attributes" on the final detail items. For example, the "flattened" form of the structure in the question should be something like:
{
"answers": [
{ "by": "success", "type2": "123", "type1": "12" }
]
}
Or even when accepting the inner array is $push only, and never updated:
{
"array": [
{ "type1": "12", "type2": "123", "answeredBy": ["success"] },
{ "type1": "12", "type2": "124", "answeredBy": [] }
]
}
Which both lend themselves to atomic updates within the scope of the positional $ operator
MongoDB 3.6 and Above
From MongoDB 3.6 there are new features available to work with nested arrays. This uses the positional filtered $[<identifier>] syntax in order to match the specific elements and apply different conditions through arrayFilters in the update statement:
Model.update(
{
"_id": 1,
"array1": {
"$elemMatch": {
"_id": "12","array2._id": "123"
}
}
},
{
"$push": { "array1.$[outer].array2.$[inner].answeredBy": "success" }
},
{
"arrayFilters": [{ "outer._id": "12" },{ "inner._id": "123" }]
}
)
The "arrayFilters" as passed to the options for .update() or even
.updateOne(), .updateMany(), .findOneAndUpdate() or .bulkWrite() method specifies the conditions to match on the identifier given in the update statement. Any elements that match the condition given will be updated.
Because the structure is "nested", we actually use "multiple filters" as is specified with an "array" of filter definitions as shown. The marked "identifier" is used in matching against the positional filtered $[<identifier>] syntax actually used in the update block of the statement. In this case inner and outer are the identifiers used for each condition as specified with the nested chain.
This new expansion makes the update of nested array content possible, but it does not really help with the practicality of "querying" such data, so the same caveats apply as explained earlier.
You typically really "mean" to express as "attributes", even if your brain initially thinks "nesting", it's just usually a reaction to how you believe the "previous relational parts" come together. In reality you really need more denormalization.
Also see How to Update Multiple Array Elements in mongodb, since these new update operators actually match and update "multiple array elements" rather than just the first, which has been the previous action of positional updates.
NOTE Somewhat ironically, since this is specified in the "options" argument for .update() and like methods, the syntax is generally compatible with all recent release driver versions.
However this is not true of the mongo shell, since the way the method is implemented there ( "ironically for backward compatibility" ) the arrayFilters argument is not recognized and removed by an internal method that parses the options in order to deliver "backward compatibility" with prior MongoDB server versions and a "legacy" .update() API call syntax.
So if you want to use the command in the mongo shell or other "shell based" products ( notably Robo 3T ) you need a latest version from either the development branch or production release as of 3.6 or greater.
See also positional all $[] which also updates "multiple array elements" but without applying to specified conditions and applies to all elements in the array where that is the desired action.
I know this is a very old question, but I just struggled with this problem myself, and found, what I believe to be, a better answer.
A way to solve this problem is to use Sub-Documents. This is done by nesting schemas within your schemas
MainSchema = new mongoose.Schema({
array1: [Array1Schema]
})
Array1Schema = new mongoose.Schema({
array2: [Array2Schema]
})
Array2Schema = new mongoose.Schema({
answeredBy": [...]
})
This way the object will look like the one you show, but now each array are filled with sub-documents. This makes it possible to dot your way into the sub-document you want. Instead of using a .update you then use a .find or .findOne to get the document you want to update.
Main.findOne((
{
_id: 1
}
)
.exec(
function(err, result){
result.array1.id(12).array2.id(123).answeredBy.push('success')
result.save(function(err){
console.log(result)
});
}
)
Haven't used the .push() function this way myself, so the syntax might not be right, but I have used both .set() and .remove(), and both works perfectly fine.
I am trying to update a value in the nested array but can't get it to work.
My object is like this
{
"_id": {
"$oid": "1"
},
"array1": [
{
"_id": "12",
"array2": [
{
"_id": "123",
"answeredBy": [], // need to push "success"
},
{
"_id": "124",
"answeredBy": [],
}
],
}
]
}
I need to push a value to "answeredBy" array.
In the below example, I tried pushing "success" string to the "answeredBy" array of the "123 _id" object but it does not work.
callback = function(err,value){
if(err){
res.send(err);
}else{
res.send(value);
}
};
conditions = {
"_id": 1,
"array1._id": 12,
"array2._id": 123
};
updates = {
$push: {
"array2.$.answeredBy": "success"
}
};
options = {
upsert: true
};
Model.update(conditions, updates, options, callback);
I found this link, but its answer only says I should use object like structure instead of array's. This cannot be applied in my situation. I really need my object to be nested in arrays
It would be great if you can help me out here. I've been spending hours to figure this out.
Thank you in advance!
General Scope and Explanation
There are a few things wrong with what you are doing here. Firstly your query conditions. You are referring to several _id values where you should not need to, and at least one of which is not on the top level.
In order to get into a "nested" value and also presuming that _id value is unique and would not appear in any other document, you query form should be like this:
Model.update(
{ "array1.array2._id": "123" },
{ "$push": { "array1.0.array2.$.answeredBy": "success" } },
function(err,numAffected) {
// something with the result in here
}
);
Now that would actually work, but really it is only a fluke that it does as there are very good reasons why it should not work for you.
The important reading is in the official documentation for the positional $ operator under the subject of "Nested Arrays". What this says is:
The positional $ operator cannot be used for queries which traverse more than one array, such as queries that traverse arrays nested within other arrays, because the replacement for the $ placeholder is a single value
Specifically what that means is the element that will be matched and returned in the positional placeholder is the value of the index from the first matching array. This means in your case the matching index on the "top" level array.
So if you look at the query notation as shown, we have "hardcoded" the first ( or 0 index ) position in the top level array, and it just so happens that the matching element within "array2" is also the zero index entry.
To demonstrate this you can change the matching _id value to "124" and the result will $push an new entry onto the element with _id "123" as they are both in the zero index entry of "array1" and that is the value returned to the placeholder.
So that is the general problem with nesting arrays. You could remove one of the levels and you would still be able to $push to the correct element in your "top" array, but there would still be multiple levels.
Try to avoid nesting arrays as you will run into update problems as is shown.
The general case is to "flatten" the things you "think" are "levels" and actually make theses "attributes" on the final detail items. For example, the "flattened" form of the structure in the question should be something like:
{
"answers": [
{ "by": "success", "type2": "123", "type1": "12" }
]
}
Or even when accepting the inner array is $push only, and never updated:
{
"array": [
{ "type1": "12", "type2": "123", "answeredBy": ["success"] },
{ "type1": "12", "type2": "124", "answeredBy": [] }
]
}
Which both lend themselves to atomic updates within the scope of the positional $ operator
MongoDB 3.6 and Above
From MongoDB 3.6 there are new features available to work with nested arrays. This uses the positional filtered $[<identifier>] syntax in order to match the specific elements and apply different conditions through arrayFilters in the update statement:
Model.update(
{
"_id": 1,
"array1": {
"$elemMatch": {
"_id": "12","array2._id": "123"
}
}
},
{
"$push": { "array1.$[outer].array2.$[inner].answeredBy": "success" }
},
{
"arrayFilters": [{ "outer._id": "12" },{ "inner._id": "123" }]
}
)
The "arrayFilters" as passed to the options for .update() or even
.updateOne(), .updateMany(), .findOneAndUpdate() or .bulkWrite() method specifies the conditions to match on the identifier given in the update statement. Any elements that match the condition given will be updated.
Because the structure is "nested", we actually use "multiple filters" as is specified with an "array" of filter definitions as shown. The marked "identifier" is used in matching against the positional filtered $[<identifier>] syntax actually used in the update block of the statement. In this case inner and outer are the identifiers used for each condition as specified with the nested chain.
This new expansion makes the update of nested array content possible, but it does not really help with the practicality of "querying" such data, so the same caveats apply as explained earlier.
You typically really "mean" to express as "attributes", even if your brain initially thinks "nesting", it's just usually a reaction to how you believe the "previous relational parts" come together. In reality you really need more denormalization.
Also see How to Update Multiple Array Elements in mongodb, since these new update operators actually match and update "multiple array elements" rather than just the first, which has been the previous action of positional updates.
NOTE Somewhat ironically, since this is specified in the "options" argument for .update() and like methods, the syntax is generally compatible with all recent release driver versions.
However this is not true of the mongo shell, since the way the method is implemented there ( "ironically for backward compatibility" ) the arrayFilters argument is not recognized and removed by an internal method that parses the options in order to deliver "backward compatibility" with prior MongoDB server versions and a "legacy" .update() API call syntax.
So if you want to use the command in the mongo shell or other "shell based" products ( notably Robo 3T ) you need a latest version from either the development branch or production release as of 3.6 or greater.
See also positional all $[] which also updates "multiple array elements" but without applying to specified conditions and applies to all elements in the array where that is the desired action.
I know this is a very old question, but I just struggled with this problem myself, and found, what I believe to be, a better answer.
A way to solve this problem is to use Sub-Documents. This is done by nesting schemas within your schemas
MainSchema = new mongoose.Schema({
array1: [Array1Schema]
})
Array1Schema = new mongoose.Schema({
array2: [Array2Schema]
})
Array2Schema = new mongoose.Schema({
answeredBy": [...]
})
This way the object will look like the one you show, but now each array are filled with sub-documents. This makes it possible to dot your way into the sub-document you want. Instead of using a .update you then use a .find or .findOne to get the document you want to update.
Main.findOne((
{
_id: 1
}
)
.exec(
function(err, result){
result.array1.id(12).array2.id(123).answeredBy.push('success')
result.save(function(err){
console.log(result)
});
}
)
Haven't used the .push() function this way myself, so the syntax might not be right, but I have used both .set() and .remove(), and both works perfectly fine.
I have a reviews collection and a users collection. In the users collection I have docs that have an array called reviews that contains the _ids of the review from the reviews collection. Sometimes I go to the mongo terminal and delete reviews from the reviews collection that I don't want from the reviews collection. for example I would delete all that don't have a specific field. the problem is I would also like to delete the review id in the reviews array. I do a simple db.collection.remove on the reviews collection so that is easy.(that would delete like 50 reviews). I was wondering how to remove ids in the reviews array easily. Any ideas? I use mongoose but I was wondering if there was an easy way to do in the terminal. I think the only association is the ids.
I no how to use $pull but I want to make it pull the ids every time a specific review is removed.
You certainly can't do this with a single atomic update as you have two collections to update. What you can do is carry out two operations in series i.e. the removal of the specific reviews from the reviews collection and then use the $pullAll operator to delete the values from reviews array in the users collection.
The following mongo shell example shows this:
var reviewIds = [
ObjectId("582ebf010936ac3ba5cd00e2"),
ObjectId("582ebf010936ac3ba5cd00e3"),
...
];
db.reviews.remove({ "_id": { "$in": reviewIds } });
db.users.updateMany(
{ "reviews": { "$in": reviewIds } },
{ "$pullAll": { "reviews": reviewIds } }
);
For a single review id, you can just use the $pull operator as
db.reviews.remove({ "_id": reviewId });
db.users.updateMany(
{ "reviews": reviewIds },
{ "$pull": { "reviews": reviewId } }
);
I have a group document defined as this in Mongoose:
var GroupSchema = new Schema({
name: String,
sections: [{type: ObjectId}]
});
As visible, group contains an array of sections. I also have another array of objectId's called archived_sections
I want to find all groups whose at least one section is NOT in archived_sections array. How to do that?
I was trying to use $nin operator like this:
Group.find({ sections: { $nin: archived_sections }).exec(function(err, groups){
res.send(groups);
});
But this is giving me only those groups whose sections field holds an array with NO elements matching an element in the array archived_sections.
I want to find all groups where at LEAST ONE section is NOT in archived_sections array. How to achieve that? Please help
You can do this by wrapping your $nin in an $elemMatch operator so that the $nin is applied separately to each element of sections instead of the set of elements as a group:
Group.find({ sections: { $elemMatch: { $nin: archived_sections } } })
.exec(function(err, groups){
res.send(groups);
}
);
If at least one element satisfies the $elemMatch query, the doc matches.
Node.JS MongoDB Driver is used.
The database entries look like that:
{
_id: ObjectId("224444202654a21928801814"),
category: "Test",
entries: [
{
_id: ObjectId("324444202dd4a21328802214"),
username: "Tester",
},
{
_id: ObjectId("324444232dd4a21328802215"),
username: "Tester2",
}
[many more...]
]
}
There are thousands of objects in the entries array.
The last array entries are the newest ones.
Now all objects should be deleted inside the entries array except the last 50 entries.
Is there a possibility to achieve that with one update/remove call? Maybe with the $slice operator?
It's not possible to achieve what you want with the $slice operator. I think using the javascript slice operator within cursor forEach() is your best bet. Try this out:
db.foo.find({}).forEach( function(doc) {
db.foo.update(
{_id:doc._id},
{$set:{entries:doc.entries.slice(doc.entries.length - 50)}}
)
})
Note: The above command would run fine in the Mongo Shell.