Allow formatting named tuples as JSON objects

src/Core/Settings.h

@@ -441,6 +441,7 @@ class IColumn;
     M(Bool, output_format_json_quote_denormals, false, "Enables '+nan', '-nan', '+inf', '-inf' outputs in JSON output format.", 0) \
     \
     M(Bool, output_format_json_escape_forward_slashes, true, "Controls escaping forward slashes for string outputs in JSON output format. This is intended for compatibility with JavaScript. Don't confuse with backslashes that are always escaped.", 0) \
+    M(Bool, output_format_json_named_tuples_as_objects, false, "Serialize named tuple columns as JSON objects.", 0) \
     \
     M(UInt64, output_format_pretty_max_rows, 10000, "Rows limit for Pretty formats.", 0) \
     M(UInt64, output_format_pretty_max_column_pad_width, 250, "Maximum width to pad all values in a column in Pretty formats.", 0) \
@@ -517,7 +518,7 @@ struct Settings : public BaseSettings<SettingsTraits>
 };
 
 /*
- * User-specified file format settings for File and ULR engines.
+ * User-specified file format settings for File and URL engines.
  */
 DECLARE_SETTINGS_TRAITS(FormatFactorySettingsTraits, FORMAT_FACTORY_SETTINGS)
 

src/DataTypes/DataTypeTuple.cpp

@@ -25,12 +25,13 @@ namespace DB
 
 namespace ErrorCodes
 {
-    extern const int LOGICAL_ERROR;
-    extern const int EMPTY_DATA_PASSED;
-    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
-    extern const int DUPLICATE_COLUMN;
     extern const int BAD_ARGUMENTS;
+    extern const int DUPLICATE_COLUMN;
+    extern const int EMPTY_DATA_PASSED;
+    extern const int LOGICAL_ERROR;
     extern const int NOT_FOUND_COLUMN_IN_BLOCK;
+    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
+    extern const int SIZES_OF_COLUMNS_IN_TUPLE_DOESNT_MATCH;
 }
 
 
@@ -145,6 +146,20 @@ static void addElementSafe(const DataTypes & elems, IColumn & column, F && impl)
     try
     {
         impl();
+
+        // Check that all columns now have the same size.
+        size_t new_size = column.size();
+        for (auto i : ext::range(1, ext::size(elems)))
+        {
+            const auto & element_column = extractElementColumn(column, i);
+            if (element_column.size() != new_size)
+            {
+                // This is not a logical error because it may work with
+                // user-supplied data.
+                throw Exception(ErrorCodes::SIZES_OF_COLUMNS_IN_TUPLE_DOESNT_MATCH,
+                    "Cannot read a tuple because not all elements are present");
+            }
+        }
     }
     catch (...)
     {
@@ -213,6 +228,24 @@ void DataTypeTuple::deserializeText(IColumn & column, ReadBuffer & istr, const F
 
 void DataTypeTuple::serializeTextJSON(const IColumn & column, size_t row_num, WriteBuffer & ostr, const FormatSettings & settings) const
 {
+    if (settings.json.named_tuples_as_objects
+        && have_explicit_names)
+    {
+        writeChar('{', ostr);
+        for (const auto i : ext::range(0, ext::size(elems)))
+        {
+            if (i != 0)
+            {
+                writeChar(',', ostr);
+            }
+            writeJSONString(names[i], ostr, settings);
+            writeChar(':', ostr);
+            elems[i]->serializeAsTextJSON(extractElementColumn(column, i), row_num, ostr, settings);
+        }
+        writeChar('}', ostr);
+    }
+    else
+    {
         writeChar('[', ostr);
         for (const auto i : ext::range(0, ext::size(elems)))
         {
@@ -221,10 +254,47 @@ void DataTypeTuple::serializeTextJSON(const IColumn & column, size_t row_num, Wr
             elems[i]->serializeAsTextJSON(extractElementColumn(column, i), row_num, ostr, settings);
         }
         writeChar(']', ostr);
+    }
 }
 
 void DataTypeTuple::deserializeTextJSON(IColumn & column, ReadBuffer & istr, const FormatSettings & settings) const
 {
+    if (settings.json.named_tuples_as_objects
+        && have_explicit_names)
+    {
+        skipWhitespaceIfAny(istr);
+        assertChar('{', istr);
+        skipWhitespaceIfAny(istr);
+
+        addElementSafe(elems, column, [&]
+        {
+            // Require all elements but in arbitrary order.
+            for (auto i : ext::range(0, ext::size(elems)))
+            {
+                if (i > 0)
+                {
+                    skipWhitespaceIfAny(istr);
+                    assertChar(',', istr);
+                    skipWhitespaceIfAny(istr);
+                }
+
+                std::string name;
+                readDoubleQuotedString(name, istr);
+                skipWhitespaceIfAny(istr);
+                assertChar(':', istr);
+                skipWhitespaceIfAny(istr);
+
+                const size_t element_pos = getPositionByName(name);
+                auto & element_column = extractElementColumn(column, element_pos);
+                elems[element_pos]->deserializeAsTextJSON(element_column, istr, settings);
+            }
+        });
+
+        skipWhitespaceIfAny(istr);
+        assertChar('}', istr);
+    }
+    else
+    {
         const size_t size = elems.size();
         assertChar('[', istr);
 
@@ -244,6 +314,7 @@ void DataTypeTuple::deserializeTextJSON(IColumn & column, ReadBuffer & istr, con
 
         skipWhitespaceIfAny(istr);
         assertChar(']', istr);
+    }
 }
 
 void DataTypeTuple::serializeTextXML(const IColumn & column, size_t row_num, WriteBuffer & ostr, const FormatSettings & settings) const

src/Formats/FormatFactory.cpp

@@ -79,6 +79,7 @@ FormatSettings getFormatSettings(const Context & context,
     format_settings.input_allow_errors_num = settings.input_format_allow_errors_num;
     format_settings.input_allow_errors_ratio = settings.input_format_allow_errors_ratio;
     format_settings.json.escape_forward_slashes = settings.output_format_json_escape_forward_slashes;
+    format_settings.json.named_tuples_as_objects = settings.output_format_json_named_tuples_as_objects;
     format_settings.json.quote_64bit_integers = settings.output_format_json_quote_64bit_integers;
     format_settings.json.quote_denormals = settings.output_format_json_quote_denormals;
     format_settings.null_as_default = settings.input_format_null_as_default;

src/Formats/FormatSettings.h

@@ -89,6 +89,7 @@ struct FormatSettings
         bool quote_64bit_integers = true;
         bool quote_denormals = true;
         bool escape_forward_slashes = true;
+        bool named_tuples_as_objects = false;
         bool serialize_as_strings = false;
     } json;
 

src/Functions/tuple.cpp

@@ -66,9 +66,13 @@ public:
             names.emplace_back(argument.name);
         }
 
-        /// Create named tuple if possible.
+        /// Create named tuple if possible. We don't print tuple element names
+        /// because they are bad anyway -- aliases are not used, e.g. tuple(1 a)
+        /// will have element name '1' and not 'a'. If we ever change this, and
+        /// add the ability to access tuple elements by name, like tuple(1 a).a,
+        /// we should probably enable printing for better discoverability.
         if (DataTypeTuple::canBeCreatedWithNames(names))
-            return std::make_shared<DataTypeTuple>(types, names, false);
+            return std::make_shared<DataTypeTuple>(types, names, false /*print names*/);
 
         return std::make_shared<DataTypeTuple>(types);
     }

src/IO/ReadHelpers.cpp

@@ -493,8 +493,12 @@ template <char quote, bool enable_sql_style_quoting, typename Vector>
 static void readAnyQuotedStringInto(Vector & s, ReadBuffer & buf)
 {
     if (buf.eof() || *buf.position() != quote)
-        throw Exception("Cannot parse quoted string: expected opening quote",
+    {
-            ErrorCodes::CANNOT_PARSE_QUOTED_STRING);
+        throw Exception(ErrorCodes::CANNOT_PARSE_QUOTED_STRING,
+            "Cannot parse quoted string: expected opening quote '{}', got '{}'",
+            std::string{quote}, buf.eof() ? "EOF" : std::string{*buf.position()});
+    }
+
     ++buf.position();
 
     while (!buf.eof())

tests/queries/0_stateless/01499_json_named_tuples.reference

@@ -0,0 +1,3 @@
+{"c":{"a":0,"b":0}}
+{"c":{"a":1,"b":2}}
+{"c":{"a":2,"b":4}}

tests/queries/0_stateless/01499_json_named_tuples.sql

@@ -0,0 +1,6 @@
+create table named_tuples engine File(JSONEachRow)
+    settings output_format_json_named_tuples_as_objects = 1
+    as select cast(tuple(number, number * 2), 'Tuple(a int, b int)') c
+        from numbers(3);
+
+select * from named_tuples format JSONEachRow settings output_format_json_named_tuples_as_objects = 1;