MongoDB Aggregation How to get total records count

Question

I have used aggregation for fetching records from mongodb    result    collection- gt aggregate array    array   match    gt   document     array   group    gt  array   id    gt    book id    date    gt  array   max    gt    book viewed      views    gt  array   sum    gt  1       array   sort    gt   sort     array   skip    gt   skip     array   limit    gt   limit         If I execute this query without limit then 10 records will be fetched  But I want to keep limit as 2  So I would like to get the total records count  How can I do with aggregation  Please advice me  Thanks

User · Answer

Sorry  but I think you need two queries  One for total views and another one for grouped records   You can find useful this answer

User · Answer

I did it this way    db collection aggregate           match     score      gt   70   lte   90                group     id  null  count     sum  1           map function record  index           print index          The aggregate will return the array so just loop it and get the final index    And other way of doing it is   var count   0   db collection aggregate      match     score      gt   70   lte   90           group     id  null  count     sum  1           map function record  index           count         print count

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Solution provided by  Divergent does work  but in my experience it is better to have 2 queries    First for filtering and then grouping by ID to get number of filtered elements  Do not filter here  it is unnecessary  Second query which filters  sorts and paginates    Solution with pushing   ROOT and using  slice runs into document memory limitation of 16MB for large collections  Also  for large collections two queries together seem to run faster than the one with   ROOT pushing  You can run them in parallel as well  so you are limited only by the slower of the two queries  probably the one which sorts    I have settled with this solution using 2 queries and aggregation framework  note - I use node js in this example  but idea is the same    var aggregation                If you can match fields at the begining  match as many as early as possible       match                        Projection       project                        Some things you can match only after projection or grouping  so do it now       match                    Copy filtering elements from the pipeline - this is the same for both counting number of fileter elements and for pagination queries  var aggregationPaginated   aggregation slice 0       Count filtered elements  aggregation push           group           id  null        count     sum  1                    Sort in pagination query  aggregationPaginated push           sort  sorting            Paginate  aggregationPaginated push           limit  skip   length               skip  skip            I use mongoose      Get total count  model count function errCount  totalCount         Count filtered    model aggregate aggregation     allowDiskUse true     exec    function errFind  documents        if  errFind             Errors        res status 503         return res json            success   false           response    err counting                      else            Number of filtered elements        var numFiltered   documents 0  count            Filter  sort and pagiante        model request aggregate aggregationPaginated         allowDiskUse true         exec          function errFindP  documentsP              if  errFindP                   Errors              res status 503               return res json                  success   false                 response    err pagination                                        else               return res json                  success   true                 recordsTotal   totalCount                 recordsFiltered   numFiltered                 response   documentsP

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const total count   await User find query  countDocuments      const users   await User find query  skip  offset  limit  limit  sort   sort   order   select  -password    const result   await User aggregate       match   query       sort    sort  order        project   password  0  avatarData  0  tokens  0        facet         users      skip   offset       limit   limit          totalCount                         count   count                                 console log JSON stringify result    console log result 0    return res status 200  json  users  result 0  users  total count  result 0  totalCount 0  count

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Here are some ways to get total records count while doing MongoDB Aggregation    Using  count  db collection aggregate         Other stages here       count   quot Total quot        For getting 1000 records this takes on average 2 ms and is the fastest way      Using  toArray    db collection aggregate        toArray   length  For getting 1000 records this takes on average 18 ms      Using  itcount    db collection aggregate        itcount    For getting 1000 records this takes on average 14 ms

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I needed the absolute total count after applying the aggregation  This worked for me   db mycollection aggregate                  group                  id    field1    field1   field2    field2                                      group                  id  null  count     sum  1                          Result           id    null       count    57 0

User · Answer

You can use toArray function and then get its length for total records count    db CollectionName aggregate         toArray   length

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This could be work for multiple match conditions              const query                                            facet                        cancelled                               match    orderStatus   Cancelled                                  count   cancelled                                               pending                               match    orderStatus   Pending                                  count   pending                                               total                               match    isActive  true                                 count   total                                                                                                          project                        cancelled     arrayElemAt     cancelled cancelled   0                         pending     arrayElemAt     pending pending   0                         total     arrayElemAt     total total   0                                                                              Order aggregate query   error  findRes    gt

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Use this to find total count in resulting collection   db collection aggregate       match     score      gt   70   lte   90           group     id  null  count     sum  1

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If you don t want to group  then use the following method   db collection aggregate       match     score      gt   70   lte   90           count   count

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This is one of the most commonly asked question to obtain the paginated result and the total number of results simultaneously in single query  I can t explain how I felt when I finally achieved it LOL    result    collection- gt aggregate array    array   match    gt   document     array   group    gt  array   id    gt    book id    date    gt  array   max    gt    book viewed      views    gt  array   sum    gt  1       array   sort    gt   sort       get total  AND preserve the results   array   group    gt  array   id    gt  null   total    gt  array    sum    gt  1     results    gt  array    push    gt     ROOT          apply limit and offset   array   project    gt  array   total    gt  1   results    gt  array    slice    gt  array    results    skip   length              Result will look something like this               id   null       total             results

User · Answer

Use the  count aggregation pipeline stage to get the total document count   Query    db collection aggregate                   match                                            group                                            count   totalCount                Result         totalCount    Number of records  some integer value

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Since v 3 4  i think  MongoDB has now a new aggregation pipeline operator named  facet  which in their own words      Processes multiple aggregation pipelines within a single stage on the same set of input documents  Each sub-pipeline has its own field in the output document where its results are stored as an array of documents    In this particular case  this means that one can do something like this    result    collection- gt aggregate          execute queries  group  sort              execute queries  group  sort              execute queries  group  sort          facet        paginatedResults      skip  skipPage       limit  perPage         totalCount                     count   count                          The result will be  with for ex 100 total results               paginatedResults                                 totalCount     count  100

[mongodb] MongoDB Aggregation: How to get total records count?

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