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.
Related
Desired result
I am trying to query my collection and obtain every unique combination of a batch and entry code. I don't care about anything other than these fields, the parent objects do not matter to me.
What I have tried
I tried running:
db.accountant_ledgers.aggregate( [ {"$group": { "_id": { entryCode: "$actions.entry.entryCode", batchCode: "$actions.entry.batchCode" } } } ]);
Problem
I get unexpected results when I run that query. I'm looking for a list of every unique combination of batch and entry codes, but instead I get a list of arrays? Perhaps these are the results I'm looking for, but I have no idea how to read them if they are.
Theory
I think perhaps this could have to do with the fact that these fields are nested. Each object has several actions, each action has several entries. I believe that the result from that query is just the aggregated entry and batch codes found in each object. I don't know how long the list of results is, but I'd guess it's the same number as the total number of objects in my collection (~90 million).
EDIT: I found out that there are only 182 results from my query, which is clearly significantly smaller than 90 million. My new theory is that it has found all unique objects, with the criteria for "uniqueness" being the list of the batch and entry codes that appear in their actions, which makes sense. There should be a lot of repetition in the collection.
Question
How can I achieve the result I'm looking for? I'm expecting something like:
FEE, MG
EXN, WT
ACH, 9C
...etc
Notes
I apologize if this is a bad question, I'm not sure how else to frame it. Let me know if I can improve my question at all.
Picture below shows the results of the query.
EDIT FOR ADDITIONAL INFORMATION
I can't share any sample documents, but the general structure of the data is shown (crudely) in the below image. Each Entity has several Actions, each Action has one Entry and each Entry has one Batch code and one Entry code.
List item
You are getting a list of documents (each is a map or a hash), not a list of arrays.
The GUI you are using is trying to show you the contents of each document on the top level which is maybe what is confusing.
If you run the query in mongo shell you should see a list of documents.
It looks like your inputs are documents where entry code and batch code are arrays, if so:
Edit your question to include sample documents you are querying as text
You could use $unwind to flatten those arrays before using $group.
I am working on a database of Polish verbs and I'd like to find out how to display my results such that each verb conjugation appears in the following order: 1ps (1st person singular), 2ps, 3ps, 1ppl (1st person plural, etc.), 2ppl, 3ppl. It displays fine when I insert documents:
verb "żyć/przeżyć" conjugation as array and nested document
But when I go to perform queries it jumbles all the array elements up, in the first case (I want to see them in order of array indices), and sorts the nested document elements into alphabetical order (whereas I want to see them in the order in which they were inserted).
verb "żyć/przeżyć" conjugation array/document query
This should be an easy one to solve, I hope this comes across as a reasonable beginner's question. I have searched for answers but couldn't find much info on this topic. Any and all help is greatly appreciated!
Cheers,
LC.
Your screenshots highlight two different views in MongoDB Compass.
The Schema view is based on a sampling of multiple documents and the order of the fields displayed cannot be specified. The schema analysis (as at Compass 1.7) lists fields in case-insensitive alphabetical order with the _id field at the top. Since this is an aggregate schema view based on multiple documents, the ordering of fields is not expected to reflect individual document order.
If you want to work with individual documents and field ordering you need to use the Documents view, as per your second screenshot. In addition to displaying the actual documents, this view allows you to include sort and skip options for queries:
Is it possible in MongoDB to insert a new document to the top of a collection? Normally, when creating new document, it is appended or added to the end of the collection.
Please shed some light
The order in which documents are returned from a collection is undefined behavior. Usually documents appear in the order they are inserted, but you can not rely on that. There are several circumstances which can cause the documents to get returned in a different order.
When you want documents in a specific order, you need to sort them explicitly when you search for them.
This seems like it should be very simple but I can't get it to work. I want to select all documents A where there are one or more B elements in a sub collection.
Like if a Store document had a collection of Employees. I just want to find Stores with 1 or more Employees in it.
I tried something like:
{Store.Employees:{$size:{$ne:0}}}
or
{Store.Employees:{$size:{$gt:0}}}
Just can't get it to work.
This isn't supported. You basically only can get documents in which array size is equal to the value. Range searches you can't do.
What people normally do is that they cache array length in a separate field in the same document. Then they index that field and make very efficient queries.
Of course, this requires a little bit more work from you (not forgetting to keep that length field current).
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).