mongodb aggregate query with nested arrays

Question

I am using mongodb

I have n houses, each house has streetid, houseid, neighborhoodid

{streetid,houseid,neighborhood}

{av,1,A},{av,2,A},{av,3,A}

{av,5,B},{av,6,B},{av,7,B}

{rd,1,A},{rd,22,A},{rd,33,A}

I want to group by street so that each street will have an array of neighborhoods (a street can span several neighborhoods ) and each neighborhood will have a list of houses that are in it(the houses must also belong to the street)

the result should be something like

{av,[{A ,[1,2,3]}, {B,[5,6,7]}]}

// street A spans neighborhood A and B each with its houses

{rd,[{A ,[1,22,33]}]}

// street rd spans neighborhood A with its houses

Your documents are not valid.

Sede
– Sede

2016-07-10 19:54:01 +00:00
Commented Jul 10, 2016 at 19:54 — Sede
– Sede, Commented Jul 10, 2016 at 19:54

Tan Kim Loong · Accepted Answer · 2016-07-10 20:20:42Z

1

This should work:

db.example.aggregate( [
  { 
    $group: { 
      _id:   { neighbourhood: "$neighbourhood", streetId: "$streetId" }, 
      house: { $addToSet: "$houseId" } 
    } 
  }, 
  { 
    $group: {
      _id: { street: "$_id.streetId" }, 
      housesInNeighbourHood: { $addToSet: { neighbourhoodId: "$_id.neighbourhood", houseId:"$house" } } 
    } 
  } 
])

answered Jul 10, 2016 at 20:20

Tan Kim Loong

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