SERVER-33172: Add onNull parameter to $dateToString

1 files changed, 77 insertions, 0 deletions

diff --git a/jstests/aggregation/expressions/date_to_string_on_null.js b/jstests/aggregation/expressions/date_to_string_on_null.js
new file mode 100644
index 00000000000..e5b3ec50f1b
--- /dev/null
+++ b/jstests/aggregation/expressions/date_to_string_on_null.js
@@ -0,0 +1,77 @@
+/**
+ * Tests for the $dateToString expression with the optional 'onNull' parameter.
+ */
+(function() {
+    "use strict";
+
+    const onNullValue = ISODate("2017-07-04T11:56:02Z");
+    const coll = db.date_to_string_on_null;
+    coll.drop();
+
+    assert.writeOK(coll.insert({_id: 0}));
+
+    for (let nullishValue of[null, undefined, "$missing"]) {
+        // Test that the 'onNull' value is returned when the 'date' is nullish.
+        assert.eq([{_id: 0, date: onNullValue}],
+                  coll.aggregate({
+                          $project: {
+                              date: {
+                                  $dateToString: {
+                                      date: nullishValue,
+                                      format: "%Y-%m-%d %H:%M:%S",
+                                      onNull: onNullValue
+                                  }
+                              }
+                          }
+                      })
+                      .toArray());
+
+        // Test that null is returned when the 'timezone' is nullish, regardless of the 'onNull'
+        // value.
+        assert.eq([{_id: 0, date: null}],
+                  coll.aggregate({
+                          $project: {
+                              date: {
+                                  $dateToString: {
+                                      date: "2018-02-06T11:56:02Z",
+                                      format: "%Y-%m-%d %H:%M:%S",
+                                      timezone: nullishValue,
+                                      onNull: onNullValue
+                                  }
+                              }
+                          }
+                      })
+                      .toArray());
+    }
+
+    // Test that 'onNull' can be any type, not just an ISODate.
+    for (let onNullValue of[{}, 5, "Not a date", null, undefined]) {
+        assert.eq([{_id: 0, date: onNullValue}],
+                  coll.aggregate({
+                          $project: {
+                              date: {
+                                  $dateToString: {
+                                      date: "$missing",
+                                      format: "%Y-%m-%d %H:%M:%S",
+                                      onNull: onNullValue
+                                  }
+                              }
+                          }
+                      })
+                      .toArray());
+    }
+
+    // Test that 'onNull' can be missing, resulting in no output field when used within a $project
+    // stage.
+    assert.eq(
+        [{_id: 0}],
+        coll.aggregate({
+                $project: {
+                    date: {
+                        $dateToString:
+                            {date: "$missing", format: "%Y-%m-%d %H:%M:%S", onNull: "$missing"}
+                    }
+                }
+            })
+            .toArray());
+})();