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

doc/src/sgml/func.sgml

@@ -10309,11 +10309,13 @@ table2-mapping
       </row>
       <row>
        <entry>
-         <literal>row_to_json(record [, pretty_bool])</literal>
+         <literal>row_to_json(rowval record [, pretty bool [, ignore_nulls bool] ])</literal>
        </entry>
        <entry>
          Returns the row as a JSON object. Line feeds will be added between
-         level-1 elements if <parameter>pretty_bool</parameter> is true.
+         level-1 elements if <parameter>pretty_bool</parameter> is true. Elements
+         with NULL values will be skipped when <parameter>ignore_nulls</parameter>
+         is true.
        </entry>
        <entry><literal>row_to_json(row(1,'foo'))</literal></entry>
        <entry><literal>{"f1":1,"f2":"foo"}</literal></entry>

src/backend/catalog/system_views.sql

@@ -867,3 +867,17 @@ RETURNS interval
 LANGUAGE INTERNAL
 STRICT IMMUTABLE
 AS 'make_interval';
+
+CREATE OR REPLACE FUNCTION
+  row_to_json(rowval record, pretty boolean DEFAULT false, ignore_nulls boolean DEFAULT false)
+RETURNS json
+LANGUAGE INTERNAL
+STRICT STABLE
+AS 'row_to_json';
+
+CREATE OR REPLACE FUNCTION
+  array_to_json(arrayval anyarray, pretty boolean DEFAULT false)
+RETURNS json
+LANGUAGE INTERNAL
+STRICT STABLE
+AS 'array_to_json';

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;
@@ -1687,27 +1693,11 @@ add_json(Datum val, bool is_null, StringInfo result,
 	datum_to_json(val, is_null, result, tcategory, outfuncoid, key_scalar);
 }
 
-/*
- * 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));
 }

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201409101
+#define CATALOG_VERSION_NO	201409111
 
 #endif

src/include/catalog/pg_proc.h

@@ -4203,14 +4203,10 @@ DATA(insert OID = 323 (  json_recv		   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0
 DESCR("I/O");
 DATA(insert OID = 324 (  json_send		   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 17 "114" _null_ _null_ _null_ _null_ json_send _null_ _null_ _null_ ));
 DESCR("I/O");
-DATA(insert OID = 3153 (  array_to_json    PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 114 "2277" _null_ _null_ _null_ _null_ array_to_json _null_ _null_ _null_ ));
+DATA(insert OID = 3153 (  array_to_json    PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 114 "2277 16" _null_ _null_ "{arrayval,pretty}" _null_ array_to_json _null_ _null_ _null_ ));
 DESCR("map array to json");
-DATA(insert OID = 3154 (  array_to_json    PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 114 "2277 16" _null_ _null_ _null_ _null_ array_to_json_pretty _null_ _null_ _null_ ));
-DESCR("map array to json with optional pretty printing");
-DATA(insert OID = 3155 (  row_to_json	   PGNSP PGUID 12 1 0 0 0 f f f f t f s 1 0 114 "2249" _null_ _null_ _null_ _null_ row_to_json _null_ _null_ _null_ ));
+DATA(insert OID = 3155 (  row_to_json	   PGNSP PGUID 12 1 0 0 0 f f f f t f s 3 0 114 "2249 16 16" _null_ _null_ "{rowval,pretty,ignore_nulls}" _null_ row_to_json _null_ _null_ _null_ ));
 DESCR("map row to json");
-DATA(insert OID = 3156 (  row_to_json	   PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 114 "2249 16" _null_ _null_ _null_ _null_ row_to_json_pretty _null_ _null_ _null_ ));
-DESCR("map row to json with optional pretty printing");
 DATA(insert OID = 3173 (  json_agg_transfn	 PGNSP PGUID 12 1 0 0 0 f f f f f f i 2 0 2281 "2281 2283" _null_ _null_ _null_ _null_ json_agg_transfn _null_ _null_ _null_ ));
 DESCR("json aggregate transition function");
 DATA(insert OID = 3174 (  json_agg_finalfn	 PGNSP PGUID 12 1 0 0 0 f f f f f f i 1 0 114 "2281" _null_ _null_ _null_ _null_ json_agg_finalfn _null_ _null_ _null_ ));

src/include/utils/json.h

@@ -23,9 +23,7 @@ extern Datum json_out(PG_FUNCTION_ARGS);
 extern Datum json_recv(PG_FUNCTION_ARGS);
 extern Datum json_send(PG_FUNCTION_ARGS);
 extern Datum array_to_json(PG_FUNCTION_ARGS);
-extern Datum array_to_json_pretty(PG_FUNCTION_ARGS);
 extern Datum row_to_json(PG_FUNCTION_ARGS);
-extern Datum row_to_json_pretty(PG_FUNCTION_ARGS);
 extern Datum to_json(PG_FUNCTION_ARGS);
 
 extern Datum json_agg_transfn(PG_FUNCTION_ARGS);

src/test/regress/expected/json.out

@@ -397,12 +397,70 @@ FROM rows q;
   "y":"txt3"}
 (3 rows)
 
+SELECT row_to_json(q,pretty := true)
+FROM rows q;
+ row_to_json  
+--------------
+ {"x":1,     +
+  "y":"txt1"}
+ {"x":2,     +
+  "y":"txt2"}
+ {"x":3,     +
+  "y":"txt3"}
+(3 rows)
+
 SELECT row_to_json(row((select array_agg(x) as d from generate_series(5,10) x)),false);
       row_to_json      
 -----------------------
  {"f1":[5,6,7,8,9,10]}
 (1 row)
 
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, false, false) FROM x;
+         row_to_json          
+------------------------------
+ {"a":10,"b":20,"c":30}
+ {"a":10,"b":null,"c":null}
+ {"a":null,"b":null,"c":null}
+(3 rows)
+
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, false, true) FROM x;
+      row_to_json       
+------------------------
+ {"a":10,"b":20,"c":30}
+ {"a":10}
+ {}
+(3 rows)
+
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, ignore_nulls := true) FROM x;
+      row_to_json       
+------------------------
+ {"a":10,"b":20,"c":30}
+ {"a":10}
+ {}
+(3 rows)
+
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, ignore_nulls := true, pretty := true) FROM x;
+ row_to_json 
+-------------
+ {"a":10,   +
+  "b":20,   +
+  "c":30}
+ {"a":10}
+ {}
+(3 rows)
+
 -- to_json, timestamps
 select to_json(timestamp '2014-05-28 12:22:35.614298');
            to_json            

src/test/regress/sql/json.sql

@@ -98,8 +98,32 @@ FROM generate_series(1,3) AS x;
 SELECT row_to_json(q,true)
 FROM rows q;
 
+SELECT row_to_json(q,pretty := true)
+FROM rows q;
+
 SELECT row_to_json(row((select array_agg(x) as d from generate_series(5,10) x)),false);
 
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, false, false) FROM x;
+
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, false, true) FROM x;
+
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, ignore_nulls := true) FROM x;
+
+WITH x AS (SELECT a,b,c FROM (VALUES(10,20,30),
+                             (10,NULL, NULL),
+                             (NULL, NULL, NULL)) g(a,b,c))
+ SELECT row_to_json(x, ignore_nulls := true, pretty := true) FROM x;
+
+
 -- to_json, timestamps
 
 select to_json(timestamp '2014-05-28 12:22:35.614298');