Following the discussion on pgsql-general, I thought I'd have a go
implementing json_array_elements_text following the same pattern as
json_each_text. The function makes it possible to join elements of a
json array onto a table, for example:
CREATE TABLE object (name TEXT PRIMARY KEY, properties JSON);
INSERT INTO object (name, properties) VALUES
('one', '{}'),
('two', '{"links": ["one"]}'),
('three', '{"links": ["one", "two"]}');
SELECT source.name, target.name
FROM (
SELECT *, json_array_elements_text(properties->'links')::text AS
link_to FROM object
) AS source
JOIN object target ON source.link_to = target.name;
My particular use case has uuid keys for object, which are difficult
to cast from json.
Laurence
---
doc/src/sgml/func.sgml | 22
src/backend/utils/adt/jsonfuncs.c| 67 +---
src/include/catalog/pg_proc.h| 2 ++
src/include/utils/json.h | 1 +
src/test/regress/expected/json.out | 34 +++---
src/test/regress/expected/json_1.out | 34 +++---
src/test/regress/sql/json.sql| 6 ++--
7 files changed, 144 insertions(+), 22 deletions(-)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index c76d357..e7338b5 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -10277,6 +10277,28 @@ table2-mapping
+ json_array_elements_text
+
+ json_array_elements_text(json)
+
+ SETOF json
+
+ Expands a JSON array to a set of JSON values. The returned value will be of
+ type text.
+
+ json_array_elements_text('["foo", "bar"]')
+
+
+ value
+---
+ foo
+ bar
+
+
+
+
+
+
json_typeof
json_typeof(json)
diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index 90fa447..b8e64f3 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -66,6 +66,9 @@ static void each_object_field_end(void *state, char *fname, bool isnull);
static void each_array_start(void *state);
static void each_scalar(void *state, char *token, JsonTokenType tokentype);
+/* common worker for json_each* functions */
+static inline Datum elements_worker(PG_FUNCTION_ARGS, bool as_text);
+
/* semantic action functions for json_array_elements */
static void elements_object_start(void *state);
static void elements_array_element_start(void *state, bool isnull);
@@ -157,6 +160,9 @@ typedef struct ElementsState
TupleDesc ret_tdesc;
MemoryContext tmp_cxt;
char *result_start;
+ bool normalize_results;
+ bool next_scalar;
+ char *normalized_scalar;
} ElementsState;
/* state for get_json_object_as_hash */
@@ -1061,7 +1067,7 @@ each_scalar(void *state, char *token, JsonTokenType tokentype)
}
/*
- * SQL function json_array_elements
+ * SQL function json_array_elements and json_array_elements_text
*
* get the elements from a json array
*
@@ -1070,10 +1076,22 @@ each_scalar(void *state, char *token, JsonTokenType tokentype)
Datum
json_array_elements(PG_FUNCTION_ARGS)
{
+ return elements_worker(fcinfo, false);
+}
+
+Datum
+json_array_elements_text(PG_FUNCTION_ARGS)
+{
+ return elements_worker(fcinfo, true);
+}
+
+static inline Datum
+elements_worker(PG_FUNCTION_ARGS, bool as_text)
+{
text *json = PG_GETARG_TEXT_P(0);
- /* elements doesn't need any escaped strings, so use false here */
- JsonLexContext *lex = makeJsonLexContext(json, false);
+ /* elements only needs escaped strings when as_text */
+ JsonLexContext *lex = makeJsonLexContext(json, as_text);
JsonSemAction *sem;
ReturnSetInfo *rsi;
MemoryContext old_cxt;
@@ -1116,6 +1134,9 @@ json_array_elements(PG_FUNCTION_ARGS)
sem->array_element_start = elements_array_element_start;
sem->array_element_end = elements_array_element_end;
+ state->normalize_results = as_text;
+ state->next_scalar = false;
+
state->lex = lex;
state->tmp_cxt = AllocSetContextCreate(CurrentMemoryContext,
"json_array_elements temporary cxt",
@@ -1138,7 +1159,17 @@ elements_array_element_start(void *state, bool isnull)
/* save a pointer to where the value starts */
if (_state->lex->lex_level == 1)
- _state->result_start = _state->lex->token_start;
+ {
+ /*
+ * next_scalar will be reset in the array_element_end handler, and
+ * since we know the value is a scalar there is no danger of it being
+ * on while recursing down the tree.
+ */
+ if (_state->normalize_results && _state->lex->token_type == JSON_TOKEN_STRING)
+ _state->next_scalar = true;
+ else
+ _state->result_start = _state->lex->token_start;
+ }
}
static void
@@ -1150,7 +1181,7 @@ elements_array_element_end(void *state, bool isnull)
text *val;
HeapTuple tuple;
Datum values[1];
- static bool nulls[1] = {false};
+ bool nulls[1] = {false};
/* skip over nested objects */
if (_state->lex->
