Example of a 3 level nested lookup and projection with MongoDb. This is effectively a paged search query.

mongdb-aggregate-lookup

db.someCollection.aggregate([
   {
      "$match":{
         "$text":{
            "$search":"boundary"
         }
      }
   },
   {
      "$match":{
         "$and":[
            {
               "isExcludedFromExternalSearch":{
                  "$ne":true
               }
            },
            {
               "$nor":[
                  {
                     "shopUrl":{
                        "$in":[
                           null,
                           ""
                        ]
                     },
                     "typeUrl":{
                        "$in":[
                           null,
                           ""
                        ]
                     }
                  }
               ]
            },
            {
               "$or":[
                  {
                     "shopUrl":{
                        "$regex":"^.{1,}$",
                        "$options":"s"
                     }
                  },
                  {
                     "typeUrl":{
                        "$regex":"^.{1,}$",
                        "$options":"s"
                     }
                  }
               ]
            },
            {
               "$or":[
                  {

                  },
                  {
                     "productFamilyId":{
                        "$in":[

                        ]
                     }
                  }
               ]
            }
         ]
      }
   },
   {
      "$addFields":{
         "score":{
            "$meta":"textScore"
         }
      }
   },
   {
      "$sort":{
         "Score":{
            "$meta":"textScore"
         }
      }
   },
   {
      "$skip":10
   },
   {
      "$limit":11
   },
   {
      "$lookup":{
         "from":"products",
         "localField":"productTypeId",
         "foreignField":"productTypeId",
         "as":"products"
      }
   },
   {
      "$lookup":{
         "from":"deliveries",
         "let":{
            "products":"$products"
         },
         "pipeline":[
            {
               "$match":{
                  "$expr":{
                     "$and":[
                        {
                           "$in":[
                              "$productId",
                              "$$products.productId"
                           ]
                        },
                        {
                           "$eq":[
                              "$deliveryType",
                              "Sample"
                           ]
                        },
                        {
                           "$eq":[
                              "$availability",
                              "Released"
                           ]
                        }
                     ]
                  }
               }
            }
         ],
         "as":"deliveries"
      }
   },
   {
      "$project":{
         "description":"$externalProductTypeDesc",
         "productTypeId":"$productTypeId",
         "id":"$_id",
         "name":"$name",
         "productFamilyId":"$productFamilyId",
         "isExternalUrl":{
            "$or":[
               {
                  "$eq":[
                     {
                        "$ifNull":[
                           "$shopUrl",
                           ""
                        ]
                     },
                     null
                  ]
               },
               {
                  "$eq":[
                     {
                        "$ifNull":[
                           "$shopUrl",
                           ""
                        ]
                     },
                     ""
                  ]
               }
            ]
         },
         "url":{
            "$ifNull":[
               "$shopUrl",
               "$typeUrl"
            ]
         },
         "score":"$score",
         "products":{
            "$filter":{
               "input":{
                  "$map":{
                     "input":"$products",
                     "as":"productForSelect",
                     "in":{
                        "productId":"$$productForSelect.productId",
                        "productInfo":"$$productForSelect.productInfo",
                        "productName":"$$productForSelect.productName",
                        "deliveries":{
                           "$map":{
                              "input":{
                                 "$filter":{
                                    "input":"$deliveries",
                                    "as":"deliveryForWhere",
                                    "cond":{
                                       "$eq":[
                                          "$$deliveryForWhere.productId",
                                          "$$productForSelect.productId"
                                       ]
                                    }
                                 }
                              },
                              "as":"deliveryForSelect",
                              "in":{
                                 "deliveryId":"$$deliveryForSelect.deliveryId",
                                 "language":"$$deliveryForSelect.language",
                                 "platform":"$$deliveryForSelect.platform",
                                 "operatingSystem":"$$deliveryForSelect.operatingSystem",
                                 "releaseInfo":"$$deliveryForSelect.releaseInfo"
                              }
                           }
                        }
                     }
                  }
               },
               "as":"productSearchResult",
               "cond":{
                  "$and":[
                     {
                        "$ne":[
                           "$$productSearchResult.deliveries",
                           null
                        ]
                     },
                     {
                        "$gt":[
                           {
                              "$size":"$$productSearchResult.deliveries"
                           },
                           0
                        ]
                     }
                  ]
               }
            }
         },
         "_id":0
      }
   }
]
);