Add 'ignore_nulls' option to row_to_json

Provide an option to skip NULL values in a row when generating a JSON
object from that row with row_to_json.  This can reduce the size of the
JSON object in cases where columns are NULL without really reducing the
information in the JSON object.

This also makes row_to_json into a single function with default values,
rather than having multiple functions.  In passing, change array_to_json
to also be a single function with default values (we don't add an
'ignore_nulls' option yet- it's not clear that there is a sensible
use-case there, and it hasn't been asked for in any case).

Pavel Stehule

1 files changed, 15 insertions, 40 deletions

diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 494a0285267..19d74014ef5 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -79,7 +79,8 @@ static void report_invalid_token(JsonLexContext *lex);
 static int	report_json_context(JsonLexContext *lex);
 static char *extract_mb_char(char *s);
 static void composite_to_json(Datum composite, StringInfo result,
-				  bool use_line_feeds);
+				  bool use_line_feeds,
+				  bool ignore_nulls);
 static void array_dim_to_json(StringInfo result, int dim, int ndims, int *dims,
 				  Datum *vals, bool *nulls, int *valcount,
 				  JsonTypeCategory tcategory, Oid outfuncoid,
@@ -1362,7 +1363,7 @@ datum_to_json(Datum val, bool is_null, StringInfo result,
 			array_to_json_internal(val, result, false);
 			break;
 		case JSONTYPE_COMPOSITE:
-			composite_to_json(val, result, false);
+			composite_to_json(val, result, false, false);
 			break;
 		case JSONTYPE_BOOL:
 			outputstr = DatumGetBool(val) ? "true" : "false";
@@ -1591,7 +1592,8 @@ array_to_json_internal(Datum array, StringInfo result, bool use_line_feeds)
  * Turn a composite / record into JSON.
  */
 static void
-composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
+composite_to_json(Datum composite, StringInfo result, bool use_line_feeds,
+				  bool ignore_nulls)
 {
 	HeapTupleHeader td;
 	Oid			tupType;
@@ -1630,6 +1632,12 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 		if (tupdesc->attrs[i]->attisdropped)
 			continue;
 
+		val = heap_getattr(tuple, i + 1, tupdesc, &isnull);
+
+		/* Don't serialize NULL field when we don't want it */
+		if (isnull && ignore_nulls)
+			continue;
+
 		if (needsep)
 			appendStringInfoString(result, sep);
 		needsep = true;
@@ -1638,8 +1646,6 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
 		escape_json(result, attname);
 		appendStringInfoChar(result, ':');
 
-		val = heap_getattr(tuple, i + 1, tupdesc, &isnull);
-
 		if (isnull)
 		{
 			tcategory = JSONTYPE_NULL;
@@ -1688,26 +1694,10 @@ add_json(Datum val, bool is_null, StringInfo result,
 }
 
 /*
- * SQL function array_to_json(row)
- */
-extern Datum
-array_to_json(PG_FUNCTION_ARGS)
-{
-	Datum		array = PG_GETARG_DATUM(0);
-	StringInfo	result;
-
-	result = makeStringInfo();
-
-	array_to_json_internal(array, result, false);
-
-	PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
-}
-
-/*
  * SQL function array_to_json(row, prettybool)
  */
 extern Datum
-array_to_json_pretty(PG_FUNCTION_ARGS)
+array_to_json(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
 	bool		use_line_feeds = PG_GETARG_BOOL(1);
@@ -1721,34 +1711,19 @@ array_to_json_pretty(PG_FUNCTION_ARGS)
 }
 
 /*
- * SQL function row_to_json(row)
+ * SQL function row_to_json(rowval record, pretty bool, ignore_nulls bool)
  */
 extern Datum
 row_to_json(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
-	StringInfo	result;
-
-	result = makeStringInfo();
-
-	composite_to_json(array, result, false);
-
-	PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
-}
-
-/*
- * SQL function row_to_json(row, prettybool)
- */
-extern Datum
-row_to_json_pretty(PG_FUNCTION_ARGS)
-{
-	Datum		array = PG_GETARG_DATUM(0);
 	bool		use_line_feeds = PG_GETARG_BOOL(1);
+	bool		ignore_nulls = PG_GETARG_BOOL(2);
 	StringInfo	result;
 
 	result = makeStringInfo();
 
-	composite_to_json(array, result, use_line_feeds);
+	composite_to_json(array, result, use_line_feeds, ignore_nulls);
 
 	PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
 }