implement aggregations on nested fields

CHANGELOG.md

@@ -4,9 +4,18 @@ This changelog documents the changes between release versions.
 
 ## [Unreleased]
 
+### Added
+
+- You can now aggregate values in nested object fields ([#136](https://github.com/hasura/ndc-mongodb/pull/136))
+
+### Changed
+
+- Result types for aggregation operations other than count are now nullable ([#136](https://github.com/hasura/ndc-mongodb/pull/136))
+
 ### Fixed
 
 - Upgrade dependencies to get fix for RUSTSEC-2024-0421, a vulnerability in domain name comparisons ([#138](https://github.com/hasura/ndc-mongodb/pull/138))
+- Aggregations on empty document sets now produce `null` instead of failing with an error ([#136](https://github.com/hasura/ndc-mongodb/pull/136))
 
 #### Fix for RUSTSEC-2024-0421 / CVE-2024-12224
 

crates/integration-tests/src/tests/aggregation.rs

@@ -101,3 +101,103 @@ async fn aggregates_mixture_of_numeric_and_null_values() -> anyhow::Result<()> {
     );
     Ok(())
 }
+
+#[tokio::test]
+async fn returns_null_when_aggregating_empty_result_set() -> anyhow::Result<()> {
+    assert_yaml_snapshot!(
+        graphql_query(
+            r#"
+            query {
+              moviesAggregate(filter_input: {where: {title: {_eq: "no such movie"}}}) {
+                runtime {
+                  avg
+                }
+              }
+            }
+            "#
+        )
+        .run()
+        .await?
+    );
+    Ok(())
+}
+
+#[tokio::test]
+async fn returns_zero_when_counting_empty_result_set() -> anyhow::Result<()> {
+    assert_yaml_snapshot!(
+        graphql_query(
+            r#"
+            query {
+              moviesAggregate(filter_input: {where: {title: {_eq: "no such movie"}}}) {
+                _count
+                title {
+                  count
+                }
+              }
+            }
+            "#
+        )
+        .run()
+        .await?
+    );
+    Ok(())
+}
+
+#[tokio::test]
+async fn returns_zero_when_counting_nested_fields_in_empty_result_set() -> anyhow::Result<()> {
+    assert_yaml_snapshot!(
+        graphql_query(
+            r#"
+            query {
+              moviesAggregate(filter_input: {where: {title: {_eq: "no such movie"}}}) {
+                awards {
+                  nominations {
+                    count
+                    _count
+                  }
+                }
+              }
+            }
+            "#
+        )
+        .run()
+        .await?
+    );
+    Ok(())
+}
+
+#[tokio::test]
+async fn aggregates_nested_field_values() -> anyhow::Result<()> {
+    assert_yaml_snapshot!(
+        graphql_query(
+            r#"
+            query {
+              moviesAggregate(
+                filter_input: {where: {title: {_in: ["Within Our Gates", "The Ace of Hearts"]}}}
+              ) {
+                tomatoes {
+                  viewer {
+                    rating {
+                      avg
+                    }
+                  }
+                  critic {
+                    rating {
+                      avg
+                    }
+                  }
+                }
+                imdb {
+                  rating {
+                    avg
+                  }
+                }
+              }
+            }
+            "#
+        )
+        .run()
+        .await?
+    );
+    Ok(())
+}

crates/integration-tests/src/tests/snapshots/integration_tests__tests__aggregation__aggregates_nested_field_values.snap

@@ -0,0 +1,17 @@
+---
+source: crates/integration-tests/src/tests/aggregation.rs
+expression: "graphql_query(r#\"\n            query {\n              moviesAggregate(\n                filter_input: {where: {title: {_in: [\"Within Our Gates\", \"The Ace of Hearts\"]}}}\n              ) {\n                tomatoes {\n                  viewer {\n                    rating {\n                      avg\n                    }\n                  }\n                  critic {\n                    rating {\n                      avg\n                    }\n                  }\n                }\n                imdb {\n                  rating {\n                    avg\n                  }\n                }\n              }\n            }\n            \"#).run().await?"
+---
+data:
+  moviesAggregate:
+    tomatoes:
+      viewer:
+        rating:
+          avg: 3.45
+      critic:
+        rating:
+          avg: ~
+    imdb:
+      rating:
+        avg: 6.65
+errors: ~

crates/integration-tests/src/tests/snapshots/integration_tests__tests__aggregation__returns_null_when_aggregating_empty_result_set.snap

@@ -0,0 +1,9 @@
+---
+source: crates/integration-tests/src/tests/aggregation.rs
+expression: "graphql_query(r#\"\n            query {\n              moviesAggregate(filter_input: {where: {title: {_eq: \"no such movie\"}}}) {\n                runtime {\n                  avg\n                }\n              }\n            }\n            \"#).run().await?"
+---
+data:
+  moviesAggregate:
+    runtime:
+      avg: ~
+errors: ~

crates/integration-tests/src/tests/snapshots/integration_tests__tests__aggregation__returns_zero_when_counting_empty_result_set.snap

@@ -0,0 +1,10 @@
+---
+source: crates/integration-tests/src/tests/aggregation.rs
+expression: "graphql_query(r#\"\n            query {\n              moviesAggregate(filter_input: {where: {title: {_eq: \"no such movie\"}}}) {\n                _count\n                title {\n                  count\n                }\n              }\n            }\n            \"#).run().await?"
+---
+data:
+  moviesAggregate:
+    _count: 0
+    title:
+      count: 0
+errors: ~

crates/integration-tests/src/tests/snapshots/integration_tests__tests__aggregation__returns_zero_when_counting_nested_fields_in_empty_result_set.snap

@@ -0,0 +1,11 @@
+---
+source: crates/integration-tests/src/tests/aggregation.rs
+expression: "graphql_query(r#\"\n            query {\n              moviesAggregate(filter_input: {where: {title: {_eq: \"no such movie\"}}}) {\n                awards {\n                  nominations {\n                    count\n                    _count\n                  }\n                }\n              }\n            }\n            \"#).run().await?"
+---
+data:
+  moviesAggregate:
+    awards:
+      nominations:
+        count: 0
+        _count: 0
+errors: ~

crates/mongodb-agent-common/src/query/mod.rs

@@ -110,11 +110,11 @@ mod tests {
             {
                 "$facet": {
                     "avg": [
-                        { "$match": { "gpa": { "$exists": true, "$ne": null } } },
+                        { "$match": { "gpa": { "$ne": null } } },
                         { "$group": { "_id": null, "result": { "$avg": "$gpa" } } },
                     ],
                     "count": [
-                        { "$match": { "gpa": { "$exists": true, "$ne": null } } },
+                        { "$match": { "gpa": { "$ne": null } } },
                         { "$group": { "_id": "$gpa" } },
                         { "$count": "result" },
                     ],
@@ -123,10 +123,17 @@ mod tests {
             {
                 "$replaceWith": {
                     "aggregates": {
-                        "avg": { "$getField": {
-                            "field": "result",
-                            "input": { "$first": { "$getField": { "$literal": "avg" } } },
-                        } },
+                        "avg": {
+                            "$ifNull": [
+                                {
+                                    "$getField": {
+                                        "field": "result",
+                                        "input": { "$first": { "$getField": { "$literal": "avg" } } },
+                                    }
+                                },
+                                null
+                            ]
+                        },
                         "count": {
                             "$ifNull": [
                                 {
@@ -180,24 +187,31 @@ mod tests {
             { "$match": { "gpa": { "$lt": 4.0 } } },
             {
                 "$facet": {
-                    "avg": [
-                        { "$match": { "gpa": { "$exists": true, "$ne": null } } },
-                        { "$group": { "_id": null, "result": { "$avg": "$gpa" } } },
-                    ],
                     "__ROWS__": [{
                         "$replaceWith": {
                             "student_gpa": { "$ifNull": ["$gpa", null] },
                         },
                     }],
+                    "avg": [
+                        { "$match": { "gpa": { "$ne": null } } },
+                        { "$group": { "_id": null, "result": { "$avg": "$gpa" } } },
+                    ],
                 },
             },
             {
                 "$replaceWith": {
                     "aggregates": {
-                        "avg": { "$getField": {
-                            "field": "result",
-                            "input": { "$first": { "$getField": { "$literal": "avg" } } },
-                        } },
+                        "avg": {
+                            "$ifNull": [
+                                {
+                                    "$getField": {
+                                        "field": "result",
+                                        "input": { "$first": { "$getField": { "$literal": "avg" } } },
+                                    }
+                                },
+                                null
+                            ]
+                        },
                     },
                     "rows": "$__ROWS__",
                 },