Subject: Re: [HACKERS] Cast jsonb to numeric, int, float, bool
To: pgsql-hackers@postgresql.org
References: <0154d35a-24ae-f063-5273-9ffcdf1c7f2e@postgrespro.ru>
From: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Message-ID: <9c013081-5dc0-1b87-a559-a0c2d405727a@postgrespro.ru>
Date: Wed, 28 Feb 2018 21:42:45 +0300
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01.02.2017 17:41, Anastasia Lubennikova:
> Now the simplest way to extract booleans and numbers from json/jsonb 
> is to cast it
> to text and then cast to the appropriate type:
>
> postgres=# select 'true'::jsonb::text::bool;
>  bool
> ------
>  t
> postgres=# select '1.0'::jsonb::text::numeric;
>  numeric
> ---------
>      1.0
>
>
> This patch implements direct casts from jsonb numeric (jbvNumeric) to 
> numeric, int4 and float8,
> and from jsonb bool (jbvBool) to bool.
>
> postgres=# select 'true'::jsonb::bool;
>  bool
> ------
>  t
>
> postgres=# select '1.0'::jsonb::numeric;
>  numeric
> ---------
>      1.0
>
>
> Waiting for your feedback.
> If you find it useful, I can also add support of json and other types, 
> such as smallint and bigint.
>
>

I totally forgot about this thread, but it is a small but useful feature.
Maybe it's time to dust it off.

This patch was made by request of one of our clients,
and though they already use custom build, I think it would be better to 
have these casts in core.

The patch is attached.
There are no tests yet, since I don't really sure what set of types do 
we want to support.
Now the patch provides jsonb to numeric, int4, float8 and bool.

Also I have some doubts about castcontext. But 'explisit' seems to be 
the correct one here.

-- 
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company


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commit 03b57ad50b9fe5bc785958bcf16badb58971d489
Author: Anastasia <a.lubennikova@postgrespro.ru>
Date:   Wed Feb 28 21:14:31 2018 +0300

    Cast jsonbNumeric to numeric, int4 and float8.
    Cast jsonbBool to bool

diff --git a/src/backend/utils/adt/jsonb.c b/src/backend/utils/adt/jsonb.c
index 0f70180..3678dbe 100644
--- a/src/backend/utils/adt/jsonb.c
+++ b/src/backend/utils/adt/jsonb.c
@@ -1845,3 +1845,129 @@ jsonb_object_agg_finalfn(PG_FUNCTION_ARGS)
 
 	PG_RETURN_POINTER(out);
 }
+
+Datum
+jsonb_numeric(PG_FUNCTION_ARGS)
+{
+	Jsonb	   *in = PG_GETARG_JSONB_P(0);
+	JsonbIterator *it;
+	JsonbValue	v;
+
+	if (!JB_ROOT_IS_OBJECT(in)
+		&& !(JB_ROOT_IS_ARRAY(in) && !JB_ROOT_IS_SCALAR(in)))
+	{
+		Assert(JB_ROOT_IS_SCALAR(in));
+
+		it = JsonbIteratorInit(&in->root);
+
+		/*
+		 * A root scalar is stored as an array of one element, so we get the
+		 * array and then its first (and only) member.
+		 */
+		(void) JsonbIteratorNext(&it, &v, true);
+		Assert(v.type == jbvArray);
+		(void) JsonbIteratorNext(&it, &v, true);
+
+		if (v.type == jbvNumeric)
+			PG_RETURN_NUMERIC(v.val.numeric);
+	}
+
+	ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+		 errmsg("key value must be json numeric")));
+}
+
+Datum
+jsonb_int4(PG_FUNCTION_ARGS)
+{
+	Jsonb	   *in = PG_GETARG_JSONB_P(0);
+	JsonbIterator *it;
+	JsonbValue	v;
+
+	if (!JB_ROOT_IS_OBJECT(in)
+		&& !(JB_ROOT_IS_ARRAY(in) && !JB_ROOT_IS_SCALAR(in)))
+	{
+		Assert(JB_ROOT_IS_SCALAR(in));
+
+		it = JsonbIteratorInit(&in->root);
+
+		/*
+		 * A root scalar is stored as an array of one element, so we get the
+		 * array and then its first (and only) member.
+		 */
+		(void) JsonbIteratorNext(&it, &v, true);
+		Assert(v.type == jbvArray);
+		(void) JsonbIteratorNext(&it, &v, true);
+
+		if (v.type == jbvNumeric)
+			PG_RETURN_INT32(DatumGetInt32(DirectFunctionCall1(numeric_int4,
+										  NumericGetDatum(v.val.numeric))));
+	}
+
+	ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+		 errmsg("key value must be json numeric")));
+}
+
+Datum
+jsonb_float8(PG_FUNCTION_ARGS)
+{
+	Jsonb	   *in = PG_GETARG_JSONB_P(0);
+	JsonbIterator *it;
+	JsonbValue	v;
+
+	if (!JB_ROOT_IS_OBJECT(in)
+		&& !(JB_ROOT_IS_ARRAY(in) && !JB_ROOT_IS_SCALAR(in)))
+	{
+		Assert(JB_ROOT_IS_SCALAR(in));
+
+		it = JsonbIteratorInit(&in->root);
+
+		/*
+		 * A root scalar is stored as an array of one element, so we get the
+		 * array and then its first (and only) member.
+		 */
+		(void) JsonbIteratorNext(&it, &v, true);
+		Assert(v.type == jbvArray);
+		(void) JsonbIteratorNext(&it, &v, true);
+
+		if (v.type == jbvNumeric)
+			PG_RETURN_FLOAT8(DatumGetFloat8(DirectFunctionCall1(numeric_float8,
+											NumericGetDatum(v.val.numeric))));
+	}
+
+	ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+		 errmsg("key value must be json numeric")));
+}
+
+Datum
+jsonb_bool(PG_FUNCTION_ARGS)
+{
+	Jsonb	   *in = PG_GETARG_JSONB_P(0);
+	JsonbIterator *it;
+	JsonbValue	v;
+
+	if (!JB_ROOT_IS_OBJECT(in)
+		&& !(JB_ROOT_IS_ARRAY(in) && !JB_ROOT_IS_SCALAR(in)))
+	{
+		Assert(JB_ROOT_IS_SCALAR(in));
+
+		it = JsonbIteratorInit(&in->root);
+
+		/*
+		 * A root scalar is stored as an array of one element, so we get the
+		 * array and then its first (and only) member.
+		 */
+		(void) JsonbIteratorNext(&it, &v, true);
+		Assert(v.type == jbvArray);
+		(void) JsonbIteratorNext(&it, &v, true);
+
+		if (v.type == jbvBool)
+			PG_RETURN_BOOL(v.val.boolean);
+	}
+
+	ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+		 errmsg("key value must be json boolean")));
+}
diff --git a/src/include/catalog/pg_cast.h b/src/include/catalog/pg_cast.h
index b447818..ea765df 100644
--- a/src/include/catalog/pg_cast.h
+++ b/src/include/catalog/pg_cast.h
@@ -391,5 +391,10 @@ DATA(insert ( 1700 1700 1703 i f ));
 /* json to/from jsonb */
 DATA(insert (  114 3802    0 a i ));
 DATA(insert ( 3802	114    0 a i ));
+/* jsonb to numeric types */
+DATA(insert ( 3802	1700   4001 e f ));
+DATA(insert ( 3802	23     4002 e f ));
+DATA(insert ( 3802	701    4003 e f ));
+DATA(insert ( 3802	16     4004 e f ));
 
 #endif							/* PG_CAST_H */
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index c00d055..2f84978 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2477,6 +2477,15 @@ DESCR("convert int2 to numeric");
 DATA(insert OID = 1783 ( int2					PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 21 "1700" _null_ _null_ _null_ _null_ _null_ numeric_int2 _null_ _null_ _null_ ));
 DESCR("convert numeric to int2");
 
+DATA(insert OID = 4001 ( numeric			PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 1700 "3802" _null_ _null_ _null_ _null_ _null_ jsonb_numeric  _null_ _null_ _null_ ));
+DESCR("convert jsonb to numeric");
+DATA(insert OID = 4002 ( int4				PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 23 "3802" _null_ _null_ _null_ _null_ _null_ jsonb_int4  _null_ _null_ _null_ ));
+DESCR("convert jsonb to int4");
+DATA(insert OID = 4003 ( float8			PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 701 "3802" _null_ _null_ _null_ _null_ _null_ jsonb_float8  _null_ _null_ _null_ ));
+DESCR("convert jsonb to float8");
+DATA(insert OID = 4004 ( bool			PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 16 "3802" _null_ _null_ _null_ _null_ _null_ jsonb_bool  _null_ _null_ _null_ ));
+DESCR("convert jsonb to boolean");
+
 /* formatting */
 DATA(insert OID = 1770 ( to_char			PGNSP PGUID 12 1 0 0 0 f f f f t f s s 2 0 25 "1184 25" _null_ _null_ _null_ _null_  _null_ timestamptz_to_char _null_ _null_ _null_ ));
 DESCR("format timestamp with time zone to text");
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index 3e462f1..2b01f17 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -128,4 +128,10 @@ extern int32 type_maximum_size(Oid type_oid, int32 typemod);
 /* quote.c */
 extern char *quote_literal_cstr(const char *rawstr);
 
+/* jsonb.c */
+extern Datum jsonb_numeric(PG_FUNCTION_ARGS);
+extern Datum jsonb_int4(PG_FUNCTION_ARGS);
+extern Datum jsonb_float8(PG_FUNCTION_ARGS);
+extern Datum jsonb_bool(PG_FUNCTION_ARGS);
+
 #endif							/* BUILTINS_H */

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