SQL/JSON constructors

This patch introduces the SQL/JSON standard constructors for JSON:

JSON()
JSON_ARRAY()
JSON_ARRAYAGG()
JSON_OBJECT()
JSON_OBJECTAGG()

For the most part these functions provide facilities that mimic
existing json/jsonb functions. However, they also offer some useful
additional functionality. In addition to text input, the JSON() function
accepts bytea input, which it will decode and constuct a json value from.
The other functions provide useful options for handling duplicate keys
and null values.

This series of patches will be followed by a consolidated documentation
patch.

Nikita Glukhov

Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru

1 files changed, 63 insertions, 0 deletions

diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index d0b91e881db..a9547aaef15 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -2450,6 +2450,69 @@ ExecInitExprRec(Expr *node, ExprState *state,
 				break;
 			}
 
+		case T_JsonConstructorExpr:
+			{
+				JsonConstructorExpr *ctor = (JsonConstructorExpr *) node;
+				List	   *args = ctor->args;
+				ListCell   *lc;
+				int			nargs = list_length(args);
+				int			argno = 0;
+
+				if (ctor->func)
+				{
+					ExecInitExprRec(ctor->func, state, resv, resnull);
+				}
+				else
+				{
+					scratch.opcode = EEOP_JSON_CONSTRUCTOR;
+					scratch.d.json_constructor.constructor = ctor;
+					scratch.d.json_constructor.arg_values = palloc(sizeof(Datum) * nargs);
+					scratch.d.json_constructor.arg_nulls = palloc(sizeof(bool) * nargs);
+					scratch.d.json_constructor.arg_types = palloc(sizeof(Oid) * nargs);
+					scratch.d.json_constructor.nargs = nargs;
+
+					foreach(lc, args)
+					{
+						Expr	   *arg = (Expr *) lfirst(lc);
+
+						scratch.d.json_constructor.arg_types[argno] = exprType((Node *) arg);
+
+						if (IsA(arg, Const))
+						{
+							/* Don't evaluate const arguments every round */
+							Const	   *con = (Const *) arg;
+
+							scratch.d.json_constructor.arg_values[argno] = con->constvalue;
+							scratch.d.json_constructor.arg_nulls[argno] = con->constisnull;
+						}
+						else
+						{
+							ExecInitExprRec(arg, state,
+											&scratch.d.json_constructor.arg_values[argno],
+											&scratch.d.json_constructor.arg_nulls[argno]);
+						}
+						argno++;
+					}
+
+					ExprEvalPushStep(state, &scratch);
+				}
+
+				if (ctor->coercion)
+				{
+					Datum	   *innermost_caseval = state->innermost_caseval;
+					bool	   *innermost_isnull = state->innermost_casenull;
+
+					state->innermost_caseval = resv;
+					state->innermost_casenull = resnull;
+
+					ExecInitExprRec(ctor->coercion, state, resv, resnull);
+
+					state->innermost_caseval = innermost_caseval;
+					state->innermost_casenull = innermost_isnull;
+				}
+			}
+			break;
+
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));