SERVER-23410 Include millis and 'Z' when converting agg dates to strings

3 files changed, 12 insertions, 3 deletions

diff --git a/src/mongo/db/pipeline/document_value_test.cpp b/src/mongo/db/pipeline/document_value_test.cpp
index 34f993f1180..613ec1de0d1 100644
--- a/src/mongo/db/pipeline/document_value_test.cpp
+++ b/src/mongo/db/pipeline/document_value_test.cpp
@@ -1375,10 +1375,10 @@ class TimestampToString : public ToStringBase {
 /** Coerce date to string. */
 class DateToString : public ToStringBase {
     Value value() {
-        return Value(Date_t::fromMillisSinceEpoch(1234567890LL * 1000));
+        return Value(Date_t::fromMillisSinceEpoch(1234567890123LL));
     }
     string expected() {
-        return "2009-02-13T23:31:30";
+        return "2009-02-13T23:31:30.123Z";
     }  // from js
 };
 
diff --git a/src/mongo/db/pipeline/expression_test.cpp b/src/mongo/db/pipeline/expression_test.cpp
index 048dcbe769d..5dbd9ad12ee 100644
--- a/src/mongo/db/pipeline/expression_test.cpp
+++ b/src/mongo/db/pipeline/expression_test.cpp
@@ -3867,6 +3867,15 @@ TEST(ExpressionSubstrCPTest, WithMixedUnicodeAndASCIIValue) {
                           {{{Value("a∫bøßabc"_sd), Value(1), Value(4)}, Value("∫b"_sd)}});
 }
 
+TEST(ExpressionSubstrCPTest, ShouldCoerceDateToString) {
+    assertExpectedResults("$substrCP",
+                          {{{Value(Date_t::fromMillisSinceEpoch(0)), Value(0), Value(1000)},
+                            Value("1970-01-01T00:00:00.000Z"_sd)}});
+    assertExpectedResults("$substrBytes",
+                          {{{Value(Date_t::fromMillisSinceEpoch(0)), Value(0), Value(1000)},
+                            Value("1970-01-01T00:00:00.000Z"_sd)}});
+}
+
 }  // namespace SubstrCP
 
 namespace Type {
diff --git a/src/mongo/db/pipeline/value.cpp b/src/mongo/db/pipeline/value.cpp
index 2695da381d0..62e64c731e4 100644
--- a/src/mongo/db/pipeline/value.cpp
+++ b/src/mongo/db/pipeline/value.cpp
@@ -57,7 +57,7 @@ using std::stringstream;
 using std::vector;
 
 namespace {
-constexpr StringData kISOFormatString = "%Y-%m-%dT%H:%M:%S"_sd;
+constexpr StringData kISOFormatString = "%Y-%m-%dT%H:%M:%S.%LZ"_sd;
 }
 
 void ValueStorage::verifyRefCountingIfShould() const {