Merge branch 'main' into patch-47

Author: dfreniche

README.md

@@ -2,6 +2,6 @@
 
 You can access the online version [here](https://mongodb-developer.github.io/aggregation-pipeline-lab/)
 
-This website is built using [Docusaurus 2](https://docusaurus.io/), a modern static website generator. We have a lab on how to use it available on https://mongodb-developer.github.io/docusaurus-workshop/.
+This website is built using [Docusaurus 2](https://docusaurus.io/), a modern static website generator. We have a lab on how to use it available on https://mongodb-developer.github.io/docusaurus-workshop/
 
 

docs/30-simple-queries/2-match.mdx

@@ -133,7 +133,7 @@ IF pages == 100 AND totalInventory == 1 {
 }
 ```
 
-👐 Return all the `books` from 2009 that have exactly 192 pages.
+👐 Return all the `books` from 2015 that have exactly 100 pages.
 
 <details>
 <summary>Answer</summary>
@@ -146,8 +146,8 @@ IF pages == 100 AND totalInventory == 1 {
   {
     $match: {
       $and: [
-        { pages: 192 },
-        { year: 2009 }
+        { pages: 100 },
+        { year: 2015 }
       ]
     }
   }
@@ -160,8 +160,8 @@ db.books.aggregate([
   { 
     $match: {
       $and: [
-        { pages: 192 }, 
-        { year: 2009 }
+        { pages: 100 }, 
+        { year: 2015 }
       ]
     } 
   }
@@ -237,7 +237,7 @@ db.books.aggregate([
 </Tabs>
 
 
-👐 Return all the `books` from 2009 that have exactly 192 pages, using the shorthand `$and` notation:
+👐 Return all the `books` from 2015 that have exactly 100 pages, using the shorthand `$and` notation:
 
 <details>
 <summary>Answer</summary>
@@ -248,14 +248,14 @@ db.books.aggregate([
 ```js
 [
     {
-        $match: {pages: 192, year: 2009}
+        $match: {pages: 100, year: 2015}
     }
 ]
 ```
   </TabItem>
   <TabItem value="mongodb-shell" label="MongoDB Shell">
 ```js
-db.books.aggregate([{$match: {pages: 192, year: 2009}}])
+db.books.aggregate([{$match: {pages: 100, year: 2015}}])
 ```
   </TabItem>
 </Tabs>

docs/40-using-arrays/40-search-inside-objects-in-arrays.mdx

@@ -131,10 +131,7 @@ db.books.aggregate([
 </div>
 </details>
 
-## $unwind
-
-This is OK, but we get all attributes, although we're only interested in the MSRP!
-
+This is okay, but We get a list of documents with a whole bunch of attributes which looks like the following:
 
 ```js
 {
@@ -168,7 +165,13 @@ This is OK, but we get all attributes, although we're only interested in the MSR
   ]
 }
 ```
-To improve, we'll use `$unwind`:
+
+What if we are only interested in the MSRP?
+
+There is more than one way to filter the unncessary keys and values:
+
+### 1. Using $unwind aggregation stage
+See the following pipeline:
 
 <Tabs groupId="aggregations">
 <TabItem value="atlas" label="Atlas UI">
@@ -225,4 +228,60 @@ db.books.aggregate([
 
 You should get one document per attribute of the original book. All fields in these returned documents should be the same, except the ones in attributes.
 
+### 🦸 2. Using $arrayToObject operator
+
+We can also flatten the `attributes` array into an object using the `$arrayToObject` operator and then use a `$project` stage to filter unwanted fields.
+Note that `$arrayToObject` is not an aggregation stage.
+
+<Tabs groupId="aggregations">
+<TabItem value="atlas" label="Atlas UI">
+
+You need to select the `books` collection.
+
+```js
+[
+    {
+      $match: {
+        'attributes.key': 'msrp',
+        'attributes.value': 9.99
+      }
+    },
+    {
+      $addFields: {
+        attributes: {
+          $arrayToObject: {
+            $map: {
+              input: '$attributes',
+              as: 'attr',
+              in: {
+                k: '$$attr.key',
+                v: '$$attr.value'
+              }
+            }
+          }
+        }
+      }
+    },
+    {
+      $project: { title: 1, 'attributes.msrp': 1 }
+    }
+]
+```
+</TabItem>
+
+<TabItem value="mongodb-shell" label="MongoDB Shell">
+
+```js
+db.books.aggregate([
+  { $match: {_id: "0395623650"} },
+  { $unwind : "$attributes" },
+]);
+```
+
+</TabItem>
+</Tabs>
+
+🦸 Run the above aggregation to observe the difference in output as compared to using `$unwind`.
+
+
 

docs/80-modifying-results/adding-fields.mdx

@@ -7,9 +7,9 @@ import TabItem from '@theme/TabItem';
 
 # 👐 Adding New Fields to Results
 
-## $addFields
+## $set / $addFields
 
-We want to estimate the reading time for a book. But we don't have that field stored in our data. We can use `$addFields` for this. If the field exists, it'll get updated, and if it doesn't, it's added.
+We want to estimate the reading time for a book. But we don't have that field stored in our data. We can use `$set` for this. If the field exists, it'll get updated, and if it doesn't, it's added.
 
 
 <Tabs groupId="aggregations">
@@ -22,7 +22,7 @@ We want to estimate the reading time for a book. But we don't have that field st
         pages: 1,
         }
     },
-    {$addFields: {readingTimeHours: {$divide: [{$multiply: ["$pages", 2]}, 60]}}},
+    {$set: {readingTimeHours: {$divide: [{$multiply: ["$pages", 2]}, 60]}}},
 ]
 ```
 
@@ -37,7 +37,7 @@ db.books.aggregate([
         pages: 1,
         }
     },
-    {$addFields: {readingTimeHours: {$divide: [{$multiply: ["$pages", 2]}, 60]}}},
+    {$set: {readingTimeHours: {$divide: [{$multiply: ["$pages", 2]}, 60]}}},
 ])
 ```
 
@@ -62,7 +62,7 @@ db.books.aggregate([
             pages: 1,
         }
     },
-    {$addFields: {notes: "PLACEHOLDER"}}
+    {$set: {notes: "PLACEHOLDER"}}
 ]
 ```
 
@@ -78,19 +78,16 @@ db.books.aggregate([
             pages: 1,
         }
     },
-    {$addFields: {notes: "PLACEHOLDER"}}
+    {$set: {notes: "PLACEHOLDER"}}
 ])
 ```
 
 </TabItem>
 </Tabs>
 
-
-
 </div>
+</details>
 
 :::info
-[$set](https://www.mongodb.com/docs/manual/reference/operator/aggregation/set/#mongodb-pipeline-pipe.-set) is an alias for $addFields that you'll find on many older posts and documentation.
-:::
-
-</details>
+[$set](https://www.mongodb.com/docs/manual/reference/operator/aggregation/set/#mongodb-pipeline-pipe.-set) is a new alias for `$addFields`. You'll still find `$addFields` on many older posts and documentation.
+:::

docs/90-exporting-data/saving-to-collection.mdx

@@ -10,7 +10,7 @@ You can export the result of an aggregation pipeline to a different DB/collectio
 <Tabs groupId="aggregations">
 <TabItem value="atlas" label="Atlas UI">
 
-Run this from the source collection
+Run this from the source collection:
 
 ```js
 [{ $out: { db: "<output-db>", coll: "<output-collection>" } }]
@@ -93,19 +93,19 @@ Reference: [📗 `$out` documentation](https://www.mongodb.com/docs/manual/refer
 
 If the collection specified by the `$out` operation already exists, then the `$out` stage atomically replaces the existing collection with the new results collection upon completion of the aggregation.
 
-To avoid overwriting the existing collection we can use `$merge` instead of `$out`.
+To avoid overwriting the existing collection, we can use `$merge` instead of `$out`.
 
 ```
 { $merge : { into : "newCollection" } }
 ```
 
-- if the collection does not exists, it will be created
-- if it exists, new data will be added
-- if [a doc already exists](https://www.mongodb.com/docs/manual/reference/operator/aggregation/merge/#std-label-merge-whenMatched), we can replace it, keep the existing one, merge both documents cause the stage to fail or run a pipeline.
+- If the collection does not exist, it will be created.
+- If it exists, new data will be added.
+- If [a doc already exists](https://www.mongodb.com/docs/manual/reference/operator/aggregation/merge/#std-label-merge-whenMatched), we can replace it, keep the existing one, merge both documents, and cause the stage to fail or run a pipeline.
 
-This is perfect for creating [On-Demand Materialized Views](https://www.mongodb.com/docs/manual/core/materialized-views/)
+This is perfect for creating [on-demand materialized views](https://www.mongodb.com/docs/manual/core/materialized-views/)
 
-As an example, let's say we want the authors to contain all the books they've written, with all the book information. In this case, we'll do a `$lookup` to get the book information into the authors collection. We can even use the name `books` for the resulting data we're joining, shadowing the original `books` array we have in authors. This way it will look like the `books` array changes.
+As an example, let's say we want the authors to contain all the books they've written, with all the book information. In this case, we'll do a `$lookup` to get the book information into the authors collection. We can even use the name `books` for the resulting data we're joining, shadowing the original `books` array we have in authors. This way, it will look like the `books` array changes.
 
 ```js
 [
@@ -119,7 +119,7 @@ As an example, let's say we want the authors to contain all the books they've wr
 ]
 ```
 
-Now a book will look like this. You can see that the books array has been "overwritten" by the `$lookup`.
+Now, a book will look like this. You can see that the books array has been "overwritten" by the `$lookup`.
 
 ```js
 {
@@ -249,7 +249,7 @@ We can go ahead and remove the authors from the books array, as it is redundant:
 ]
 ```
 
-Now that our authors look the way we want, we can overwrite the authors collection using `$merge`
+Now that our authors look the way we want, we can overwrite the authors collection using `$merge`.
 
 ```js
 [
@@ -269,9 +269,9 @@ Now that our authors look the way we want, we can overwrite the authors collecti
 ]
 ```
 
-- we use the `_id` field to match documents
-- we replace the existing ones with `replace`
+- We use the `_id` field to match documents.
+- We replace the existing ones with `replace`.
 
 :::warning
 We should see a message telling us that the $merge operator will cause the pipeline to persist the results to the specified location. This stage changes data.
-:::
+:::

docs/lecture-material.mdx

@@ -2,7 +2,7 @@
 sidebar_position: 90
 ---
 
-# 📘 Lecture material
+# 📘 Lecture Material
 
 |||
 |-|:-|