Allow keypath to be provided as argument

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ### Enhancements
 * <New feature description> (PR [#????](https://github.com/realm/realm-core/pull/????))
-* None.
+* Property keypath in RQL can be substituted with value given as argument. Use '$P<i>' in query string. (Issue [#7033](https://github.com/realm/realm-core/issues/7033))
 
 ### Fixed
 * <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)

src/realm/parser/driver.cpp

@@ -929,6 +929,7 @@ Query TrueOrFalseNode::visit(ParserDriver* drv)
 
 std::unique_ptr<Subexpr> PropertyNode::visit(ParserDriver* drv, DataType)
 {
+    path->resolve_arg(drv);
     if (path->path_elems.back().is_key() && path->path_elems.back().get_key() == "@links") {
         identifier = "@links";
         // This is a backlink aggregate query
@@ -1610,6 +1611,23 @@ std::unique_ptr<Subexpr> ListNode::visit(ParserDriver* drv, DataType hint)
     return ret;
 }
 
+void PathNode::resolve_arg(ParserDriver* drv)
+{
+    if (arg.size()) {
+        if (path_elems.size()) {
+            throw InvalidQueryError("Key path argument cannot be mixed with other elements");
+        }
+        auto arg_str = drv->get_arg_for_key_path(arg);
+        const char* path = arg_str.data();
+        do {
+            auto p = find_chr(path, '.');
+            StringData elem(path, p - path);
+            add_element(elem);
+            path = p;
+        } while (*path++ == '.');
+    }
+}
+
 LinkChain PathNode::visit(ParserDriver* drv, util::Optional<ExpressionComparisonType> comp_type)
 {
     LinkChain link_chain(drv->m_base_table, comp_type);
@@ -1759,6 +1777,22 @@ PathElement ParserDriver::get_arg_for_index(const std::string& i)
     }
 }
 
+std::string ParserDriver::get_arg_for_key_path(const std::string& i)
+{
+    REALM_ASSERT(i[0] == '$');
+    REALM_ASSERT(i[1] == 'K');
+    size_t arg_no = size_t(strtol(i.substr(2).c_str(), nullptr, 10));
+    if (m_args.is_argument_null(arg_no) || m_args.is_argument_list(arg_no)) {
+        throw InvalidQueryArgError(util::format("Null or list cannot be used for parameter '%1'", i));
+    }
+    auto type = m_args.type_for_argument(arg_no);
+    if (type != type_String) {
+        throw InvalidQueryArgError(util::format("Invalid index type for '%1'. Expected a string, but found type '%2'",
+                                                i, get_data_type_name(type)));
+    }
+    return m_args.string_for_argument(arg_no);
+}
+
 double ParserDriver::get_arg_for_coordinate(const std::string& str)
 {
     REALM_ASSERT(str[0] == '$');

src/realm/parser/driver.hpp

@@ -278,13 +278,18 @@ class ListNode : public ValueNode {
 
 class PathNode : public ParserNode {
 public:
+    struct ArgTag {};
     Path path_elems;
     Path::iterator current_path_elem;
 
     PathNode(const PathElement& first)
     {
         add_element(first);
     }
+    PathNode(const std::string& arg_str, ArgTag)
+        : arg(arg_str)
+    {
+    }
     bool at_end() const
     {
         return current_path_elem == path_elems.end();
@@ -298,6 +303,7 @@ class PathNode : public ParserNode {
         return path_elems.back().get_key();
     }
 
+    void resolve_arg(ParserDriver*);
     LinkChain visit(ParserDriver*, util::Optional<ExpressionComparisonType> = util::none);
     void add_element(const PathElement& elem)
     {
@@ -332,6 +338,7 @@ class PathNode : public ParserNode {
     }
 
 private:
+    std::string arg;
     std::string backlink_str;
     int backlink = 0;
 };
@@ -664,6 +671,7 @@ class ParserDriver {
     }
 
     PathElement get_arg_for_index(const std::string&);
+    std::string get_arg_for_key_path(const std::string& i);
     double get_arg_for_coordinate(const std::string&);
 
     template <class T>