I'm currently trying to use MongoDB Compass to query my collection. However, I seem to be only able to filter the data.
Is there any way for me to sort the data as well? I would like to sort my data in ascending order using one of my data fields.
If MongoDB Compass isn't the best way to order a collection, what other GUI could I use?
Using MongoDB Compass 1.7 or newer, you can sort (and project, skip, or limit) results by choosing the Documents tab and expanding the Options.
To sort in ascending order by a field myField, use { myField:1 }. Any of the usual cursor sort() options can be provided, including ordering results by multiple fields.
Note: options like sort and skip are not available in the default Schema tab because this view uses sampling to find a random set of documents, as opposed to the Documents view which displays a specific query result.
Related
I am trying to sort the result of my mongoDB query and add a ranking based on that sorting. Currently I only call .find().sort({total: 1}) and this gives me the correct ordering of the documents. But is it possible to "add a field" based on that sorting (basically a ranking field, starting from 1 and counting up)? I tried googling but didnt found anything that suits for this purpose.
Thanks in advance.
Looking for a way to view the results of a query where the displayed fields in the doc are ordered (lexicographically in my case).
Example:
I'm getting back from a query one document, which is what I need. This document has 30 fields and I'm looking to see the value in one of them. My issue is that the order of the fields is, well, kinda random. Not sorted in any way I'm aware of.
When a certain query is done on a mongodb collection, if there are multiple indexes that can be used to perform the query, how does mongodb choose the index for the query?
for an example, in a 'order' collection, if there are two indexes for columns 'customer' and 'vendor', and a query is issued with both customer and vendor specified, how does mongodb decide whether to use the customer index or the vendor index?
Is there a way to instruct mongodb to prefer a certain index over another, for a given query?
When a certain query is done on a mongodb collection, if there are
multiple indexes that can be used to perform the query, how does
mongodb choose the index for the query?
You can generate a query plan for a query you are trying to analyze - see what indexes are used and how they are used. Use the explain method for this; e.g. db.collection.explain().find(). The explain takes a parameter with values "queryPlanner" (the default), "executionStats" and "allPlansExecution". Each of these have different plan output.
The query optimizer generates plans for all the indexes that could be used for a given query. In your example order collection, the two single field indexes (one each for the fields customer and vendor) are possible candidates (for a query filter with both the fields). The optimizer uses each of the plans and executes them for a certain period of time and chooses the best performing candidate (this is determined based upon factors like - which returned most documents in least time, and other factors). Based upon this it will output the winning and rejected plans and these can be viewed in the plan output. You will see one of the indexes in the winning plan and the other in the rejected plan in the output.
MongoDB caches the plans for a given query shape. Query plans are cached so that plans need not be generated and compared against each other every time a query is executed.
Is there a way to instruct mongodb to prefer a certain index over
another, for a given query?
There are couple of ways you can use:
Force MongoDB to use a specific index using the hint() method.
Set Index Filters to specify which indexes the optimizer will evaluate for a query shape. Note that this setting is not persisted after a server shutdown.
Their official website states:
MongoDB uses multikey indexes to index the content stored in arrays. If you index a field that holds an array value, MongoDB creates separate index entries for every element of the array. These multikey indexes allow queries to select documents that contain arrays by matching on element or elements of the arrays.
You can checkout This article for more information
For your second query, you can try creating custom indexes for documents. Checkout their Documentation for the same
Use case
Need to index selective documents from a mongo collection. Selection is based on the document field value. Eg., Profile collection has multiple documents, but need to index documents whose age > 25 and country is "US"
I am using mongo-connector for indexing collection (in elasticsearch)
Please suggest the approaches which can be taken?
Need to index selective documents
Using elasticsearch you decide which fields to index through mapping. So in your case, you can set all the fields except age to index: no
Elastic Search Mapping
Depending on the version of your mongo-connector, you could also use namespaces to select which documents to index. See the Configuration Options of mongo-connector. However, I don't think that conditional index is possible... at least I have never seen it.
I have collections with huge amount of Documents on which I need to do custom search with various different queries.
Each Document have boolean property. Let's call it "isInTop".
I need to show Documents which have this property first in all queries.
Yes. I can easy do sort in this field like:
.sort( { isInTop: -1 } );
And create proper index with field "isInTop" as last field in it. But this will be work slowly, as indexes in mongo works best with unique fields.
So is there is solution to show Documents with field "isInTop" on top of each query?
I see two solutions here.
First: set Documents wich need to be in top the _id from "future". As you know, ObjectId contains timestamp. So I can create ObjectId with timestamp from future and use natural order
Second: create separate collection for Ducuments wich need to be in top. And do queries in it first.
Is there is any other solutions for this problem? Which will work fater?
UPDATE
I have done this issue with sorting on custom field which represent rank.
Using the _id field trick you mention has the problem that at some point in time you will reach the special time, and you can't change the _id field (without inserting a new document and removing the old one).
Creating a special collection which just holds the ones you care about is probably the best option. It gives you the ability to logically (and to some extent, physically) separate the documents.
Newly introduced in mongodb there is also support for a "sparse" index which may fulfill your needs as well. You could only set the "isInTop" field when you want it to be special, and then create a sparse index on it which would not have the problems you would normally have with a single indexed boolean field (in btrees).