Allow variable jsonpath specifications

Author: Nikita Glukhov

src/backend/executor/execExpr.c

@@ -2050,6 +2050,13 @@ ExecInitExprRec(Expr *node, PlanState *parent, ExprState *state,
 								&scratch.d.jsonexpr.raw_expr->value,
 								&scratch.d.jsonexpr.raw_expr->isnull);
 
+				scratch.d.jsonexpr.pathspec =
+					palloc(sizeof(*scratch.d.jsonexpr.pathspec));
+
+				ExecInitExprRec((Expr *) jexpr->path_spec, parent, state,
+								&scratch.d.jsonexpr.pathspec->value,
+								&scratch.d.jsonexpr.pathspec->isnull);
+
 				scratch.d.jsonexpr.formatted_expr =
 						ExecInitExpr((Expr *) jexpr->formatted_expr, parent);
 

src/backend/executor/execExprInterp.c

@@ -3946,16 +3946,15 @@ ExecEvalJson(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
 	*op->resnull = true;		/* until we get a result */
 	*op->resvalue = (Datum) 0;
 
-	if (op->d.jsonexpr.raw_expr->isnull)
+	if (op->d.jsonexpr.raw_expr->isnull || op->d.jsonexpr.pathspec->isnull)
 	{
 		/* execute domain checks for NULLs */
 		(void) ExecEvalJsonExprCoercion(op, econtext, res, op->resnull, isjsonb);
 		return;
 	}
 
 	item = op->d.jsonexpr.raw_expr->value;
-
-	path = DatumGetJsonPathP(jexpr->path_spec->constvalue);
+	path = DatumGetJsonPathP(op->d.jsonexpr.pathspec->value);
 
 	/* reset JSON path variable contexts */
 	foreach(lc, op->d.jsonexpr.args)

src/backend/nodes/copyfuncs.c

@@ -2331,7 +2331,7 @@ _copyJsonCommon(const JsonCommon *from)
 	JsonCommon	   *newnode = makeNode(JsonCommon);
 
 	COPY_NODE_FIELD(expr);
-	COPY_STRING_FIELD(pathspec);
+	COPY_NODE_FIELD(pathspec);
 	COPY_STRING_FIELD(pathname);
 	COPY_NODE_FIELD(passing);
 	COPY_LOCATION_FIELD(location);

src/backend/parser/gram.y

@@ -626,6 +626,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 					json_table_plan_cross
 					json_table_plan_primary
 					json_table_default_plan
+					json_path_specification
 
 %type <list>		json_arguments
 					json_passing_clause_opt
@@ -637,8 +638,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 %type <typnam>		json_returning_clause_opt
 
-%type <str>			json_path_specification
-					json_table_column_path_specification_clause_opt
+%type <str>			json_table_column_path_specification_clause_opt
 					json_table_path_name
 					json_as_path_name_clause_opt
 
@@ -847,6 +847,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
  */
 %nonassoc	UNBOUNDED		/* ideally should have same precedence as IDENT */
 %nonassoc	ERROR_P EMPTY_P DEFAULT ABSENT /* JSON error/empty behavior */
+%nonassoc	COLUMNS FALSE_P KEEP OMIT PASSING TRUE_P UNKNOWN
 %nonassoc	IDENT GENERATED NULL_P PARTITION RANGE ROWS PRECEDING FOLLOWING CUBE ROLLUP
 %left		Op OPERATOR		/* multi-character ops and user-defined operators */
 %left		'+' '-'
@@ -14455,7 +14456,7 @@ json_context_item:
 		;
 
 json_path_specification:
-			Sconst									{ $$ = $1; }
+			a_expr									{ $$ = $1; }
 		;
 
 json_as_path_name_clause_opt:
@@ -14753,7 +14754,7 @@ json_table_error_clause_opt:
 		;
 
 json_table_column_path_specification_clause_opt:
-			PATH json_path_specification			{ $$ = $2; }
+			PATH Sconst								{ $$ = $2; }
 			| /* EMPTY */ %prec json_table_column	{ $$ = NULL; }
 		;
 
@@ -14785,7 +14786,7 @@ json_table_formatted_column_definition:
 		;
 
 json_table_nested_columns:
-			NESTED path_opt json_path_specification
+			NESTED path_opt Sconst
 							json_as_path_name_clause_opt
 							json_table_columns_clause
 				{

src/backend/parser/parse_clause.c

@@ -1059,6 +1059,18 @@ transformRangeTableSample(ParseState *pstate, RangeTableSample *rts)
 	return tablesample;
 }
 
+static Node *
+makeStringConst(char *str, int location)
+{
+	A_Const *n = makeNode(A_Const);
+
+	n->val.type = T_String;
+	n->val.val.str = str;
+	n->location = location;
+
+	return (Node *)n;
+}
+
 /*
  * getRTEForSpecialRelationTypes
  *
@@ -1102,6 +1114,7 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	JsonValueExpr *jvexpr = makeNode(JsonValueExpr);
 	JsonCommon *common = makeNode(JsonCommon);
 	JsonOutput *output = makeNode(JsonOutput);
+	JsonPathSpec pathspec;
 
 	jfexpr->op = jtc->coltype == JTC_REGULAR ? IS_JSON_VALUE : IS_JSON_QUERY;
 	jfexpr->common = common;
@@ -1122,7 +1135,7 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	common->passing = passingArgs;
 
 	if (jtc->pathspec)
-		common->pathspec = jtc->pathspec;
+		pathspec = jtc->pathspec;
 	else
 	{
 		/* Construct default path as '$."column_name"' */
@@ -1133,9 +1146,11 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 		appendStringInfoString(&path, "$.");
 		escape_json(&path, jtc->name);
 
-		common->pathspec = path.data;
+		pathspec = path.data;
 	}
 
+	common->pathspec = makeStringConst(pathspec, -1);
+
 	jvexpr->expr = (Expr *) contextItemExpr;
 	jvexpr->format.type = JS_FORMAT_DEFAULT;
 	jvexpr->format.encoding = JS_ENC_DEFAULT;
@@ -1629,6 +1644,7 @@ transformJsonTable(ParseState *pstate, JsonTable *jt)
 	JsonCommon *jscommon;
 	JsonTablePlan *plan = jt->plan;
 	char	   *rootPathName = jt->common->pathname;
+	char	   *rootPath;
 	bool		is_lateral;
 
 	cxt.table = jt;
@@ -1658,7 +1674,7 @@ transformJsonTable(ParseState *pstate, JsonTable *jt)
 	}
 
 	jscommon = copyObject(jt->common);
-	jscommon->pathspec = pstrdup("$");
+	jscommon->pathspec = makeStringConst(pstrdup("$"), -1);
 
 	jfe->op = IS_JSON_TABLE;
 	jfe->common = jscommon;
@@ -1682,10 +1698,19 @@ transformJsonTable(ParseState *pstate, JsonTable *jt)
 
 	cxt.contextItemTypid = exprType(tf->docexpr);
 
+	if (!IsA(jt->common->pathspec, A_Const) ||
+		castNode(A_Const, jt->common->pathspec)->val.type != T_String)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("only string constants supported in JSON_TABLE path specification"),
+				 parser_errposition(pstate,
+									exprLocation(jt->common->pathspec))));
+
+	rootPath = castNode(A_Const, jt->common->pathspec)->val.val.str;
+
 	tf->plan = (Node *) transformJsonTableColumns(pstate, &cxt, plan,
 												  jt->columns,
-												  jt->common->pathspec,
-												  &rootPathName,
+												  rootPath, &rootPathName,
 												  jt->common->location);
 
 	tf->ordinalitycol = -1;		/* undefine ordinality column number */

src/backend/parser/parse_expr.c

@@ -4353,7 +4353,7 @@ static JsonExpr *
 transformJsonExprCommon(ParseState *pstate, JsonFuncExpr *func)
 {
 	JsonExpr   *jsexpr = makeNode(JsonExpr);
-	Datum		jsonpath;
+	Node	   *pathspec;
 	JsonFormatType format;
 
 	if (func->common->pathname && func->op != IS_JSON_TABLE)
@@ -4383,12 +4383,19 @@ transformJsonExprCommon(ParseState *pstate, JsonFuncExpr *func)
 
 	jsexpr->format = func->common->expr->format;
 
-	/* parse JSON path string */
-	jsonpath = DirectFunctionCall1(jsonpath_in,
-									CStringGetDatum(func->common->pathspec));
+	pathspec = transformExprRecurse(pstate, func->common->pathspec);
 
-	jsexpr->path_spec = makeConst(JSONPATHOID, -1, InvalidOid, -1,
-								  jsonpath, false, false);
+	jsexpr->path_spec =
+		coerce_to_target_type(pstate, pathspec, exprType(pathspec),
+							  JSONPATHOID, -1,
+							  COERCION_EXPLICIT, COERCE_IMPLICIT_CAST,
+							  exprLocation(pathspec));
+	if (!jsexpr->path_spec)
+		ereport(ERROR,
+				(errcode(ERRCODE_DATATYPE_MISMATCH),
+				 errmsg("JSON path expression must be type %s, not type %s",
+						"jsonpath", format_type_be(exprType(pathspec))),
+				 parser_errposition(pstate, exprLocation(pathspec))));
 
 	/* transform and coerce to json[b] passing arguments */
 	transformJsonPassingArgs(pstate, format, func->common->passing,

src/backend/utils/adt/ruleutils.c

@@ -8837,7 +8837,10 @@ get_rule_expr(Node *node, deparse_context *context,
 
 				appendStringInfoString(buf, ", ");
 
-				get_const_expr(jexpr->path_spec, context, -1);
+				if (IsA(jexpr->path_spec, Const))
+					get_const_expr((Const *) jexpr->path_spec, context, -1);
+				else
+					get_rule_expr(jexpr->path_spec, context, false);
 
 				if (jexpr->passing.values)
 				{
@@ -9836,7 +9839,11 @@ get_json_table_columns(TableFunc *tf, JsonTableParentNode *node,
 								   " FORMAT JSONB" : " FORMAT JSON");
 
 		appendStringInfoString(buf, " PATH ");
-		get_const_expr(colexpr->path_spec, context, -1);
+
+		if (IsA(colexpr->path_spec, Const))
+			get_const_expr((Const *) colexpr->path_spec, context, -1);
+		else
+			get_rule_expr(colexpr->path_spec, context, false);
 
 		if (colexpr->wrapper == JSW_CONDITIONAL)
 			appendStringInfo(buf, " WITH CONDITIONAL WRAPPER");

src/include/executor/execExpr.h

@@ -576,7 +576,8 @@ typedef struct ExprEvalStep
 			{
 				Datum		value;
 				bool		isnull;
-			}		   *raw_expr;			/* raw context item value */
+			}		   *raw_expr,			/* raw context item value */
+					   *pathspec;			/* path specification value */
 
 			ExprState  *formatted_expr;		/* formatted context item */
 			ExprState  *result_expr;		/* coerced to output type */

src/include/nodes/parsenodes.h

@@ -1475,7 +1475,7 @@ typedef struct JsonCommon
 {
 	NodeTag		type;
 	JsonValueExpr *expr;		/* context item expression */
-	JsonPathSpec pathspec;		/* JSON path specification */
+	Node	   *pathspec;		/* JSON path specification expression */
 	char	   *pathname;		/* path name, if any */
 	List	   *passing;		/* list of PASSING clause arguments, if any */
 	int			location;		/* token location, or -1 if unknown */

src/include/nodes/primnodes.h

@@ -1288,7 +1288,7 @@ typedef struct JsonExpr
 	bool		coerce_via_io;	/* coerce result using type input function */
 	Oid			coerce_via_io_collation; /* collation for conversion through I/O */
 	JsonFormat	format;			/* context item format (JSON/JSONB) */
-	Const	   *path_spec;		/* JSON path specification */
+	Node	   *path_spec;		/* JSON path specification expression */
 	JsonPassing	passing;		/* PASSING clause arguments */
 	JsonReturning returning;	/* RETURNING clause type/format info */
 	JsonBehavior on_empty;		/* ON EMPTY behavior */