SERVER-48684 Pipeline stage $set fails to set a non-existent dotted field to an object

1 files changed, 98 insertions, 0 deletions

diff --git a/jstests/aggregation/sources/addFields/dotted_paths.js b/jstests/aggregation/sources/addFields/dotted_paths.js
new file mode 100644
index 00000000000..e8ecdc39d46
--- /dev/null
+++ b/jstests/aggregation/sources/addFields/dotted_paths.js
@@ -0,0 +1,98 @@
+/**
+ * Test the behavior of $addFields in the presence of a dotted field path.
+ */
+(function() {
+const coll = db.add_fields_dotted_paths;
+coll.drop();
+
+let initObj = {
+    _id: 1,
+    arrayField: [1, {subField: [2, {}]}, [1]],
+    objField: {p: {q: 1}, subArr: [1]},
+    otherField: "value"
+};
+assert.commandWorked(coll.insert(initObj));
+
+function assertAddFieldsResult(projection, expectedResults) {
+    assert.eq(coll.aggregate([{$addFields: projection}]).toArray(), [expectedResults]);
+}
+
+// Test that the value gets overwritten when a field exists at a given path.
+initObj["objField"]["subArr"] = "newValue";
+assertAddFieldsResult({"objField.subArr": "newValue"}, initObj);
+assertAddFieldsResult({"objField.subArr": {$literal: "newValue"}}, initObj);
+
+// Test that a new sub-object is created when a field does not exist at a given path. All the
+// existing sibling fields are retained.
+initObj["objField"] = {
+    p: {q: 1},
+    subArr: [1],  // Existing fields are retained.
+    newSubPath: {b: "newValue"}
+};
+assertAddFieldsResult({"objField.newSubPath.b": {$literal: "newValue"}}, initObj);
+assertAddFieldsResult({"objField.newSubPath.b": "newValue"}, initObj);
+
+// When the value is a nested object.
+const valueWithNestedObject = {
+    newSubObj: [{p: "newValue"}]
+};
+initObj["objField"]["newSubPath"] = {
+    b: valueWithNestedObject
+};
+assertAddFieldsResult({"objField.newSubPath.b": valueWithNestedObject}, initObj);
+assertAddFieldsResult({"objField.newSubPath.b": {$literal: valueWithNestedObject}}, initObj);
+initObj["objField"] = {
+    p: {q: 1},
+    subArr: [1]
+};  // Reset input object.
+
+// When the top level field doesn"t exist, a new nested object is created based on the given path.
+initObj["newField"] = {
+    newSubPath: {b: "newValue"}
+};
+assertAddFieldsResult({"newField.newSubPath.b": {$literal: "newValue"}}, initObj);
+assertAddFieldsResult({"newField.newSubPath.b": "newValue"}, initObj);
+
+// When the top level field doesn"t exist, a new nested object is created based on the given path
+// and the structure of the object in the value.
+initObj["newField"]["newSubPath"] = {
+    b: valueWithNestedObject
+};
+assertAddFieldsResult({"newField.newSubPath.b": valueWithNestedObject}, initObj);
+assertAddFieldsResult({"newField.newSubPath.b": {$literal: valueWithNestedObject}}, initObj);
+delete initObj["newField"];  // Reset.
+
+// Test when the path encounters an array and the value is a scalar.
+initObj["arrayField"] = {
+    newSubPath: {b: "newValue"}
+};
+let expectedSubObj = {newSubPath: {b: "newValue"}};
+initObj["arrayField"] =
+    [expectedSubObj, Object.assign({subField: [2, {}]}, expectedSubObj), [expectedSubObj]];
+assertAddFieldsResult({"arrayField.newSubPath.b": {$literal: "newValue"}}, initObj);
+assertAddFieldsResult({"arrayField.newSubPath.b": "newValue"}, initObj);
+
+// Test when the path encounters an array and the value is a nested object.
+expectedSubObj = {
+    newSubPath: {b: valueWithNestedObject}
+};
+initObj["arrayField"] =
+    [expectedSubObj, Object.assign({subField: [2, {}]}, expectedSubObj), [expectedSubObj]];
+assertAddFieldsResult({"arrayField.newSubPath.b": valueWithNestedObject}, initObj);
+assertAddFieldsResult({"arrayField.newSubPath.b": {$literal: valueWithNestedObject}}, initObj);
+
+// Test when the path encounters multiple arrays and the value is a nested object.
+expectedSubObj = {
+    subField: {b: valueWithNestedObject}
+};
+initObj["arrayField"] = [
+    expectedSubObj,
+    {
+        subField:
+            [{b: valueWithNestedObject}, {b: valueWithNestedObject}]  // Sub-array is also exploded.
+    },
+    [expectedSubObj]
+];
+assertAddFieldsResult({"arrayField.subField.b": valueWithNestedObject}, initObj);
+assertAddFieldsResult({"arrayField.subField.b": {$literal: valueWithNestedObject}}, initObj);
+})();