From 515c827073ea5088dac48d7764feb57841291255 Mon Sep 17 00:00:00 2001
From: Erez Shinan <erezshin+git@gmail.com>
Date: Fri, 28 Oct 2022 10:40:21 -0300
Subject: [PATCH] Queries: Added Param mechanism, to help speed up query
 construction.

---
 data_diff/queries/ast_classes.py | 13 ++++++++++++-
 data_diff/queries/compiler.py    | 10 +++++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/data_diff/queries/ast_classes.py b/data_diff/queries/ast_classes.py
index 88d7ab114..c283f3486 100644
--- a/data_diff/queries/ast_classes.py
+++ b/data_diff/queries/ast_classes.py
@@ -6,7 +6,7 @@
 
 from data_diff.utils import ArithString, join_iter
 
-from .compiler import Compilable, Compiler
+from .compiler import Compilable, Compiler, cv_params
 from .base import SKIP, CompileError, DbPath, Schema, args_as_tuple
 
 
@@ -38,6 +38,17 @@ def _expr_type(e: Expr) -> type:
     return type(e)
 
 
+@dataclass
+class Param(Compilable):
+    """A value placeholder, to be specified at compilation time using the `cv_params` context variable."""
+
+    name: str
+
+    def compile(self, c: Compiler) -> str:
+        params = cv_params.get()
+        return c._compile(params[self.name])
+
+
 @dataclass
 class Alias(ExprNode):
     expr: Expr
diff --git a/data_diff/queries/compiler.py b/data_diff/queries/compiler.py
index 312421319..e9a66bed1 100644
--- a/data_diff/queries/compiler.py
+++ b/data_diff/queries/compiler.py
@@ -8,10 +8,15 @@
 from data_diff.utils import ArithString
 from data_diff.databases.database_types import AbstractDialect, DbPath
 
+import contextvars
+
+cv_params = contextvars.ContextVar("params")
+
 
 @dataclass
 class Compiler:
     database: AbstractDialect
+    params: dict = {}
     in_select: bool = False  # Compilation runtime flag
     in_join: bool = False  # Compilation runtime flag
 
@@ -21,7 +26,10 @@ class Compiler:
 
     _counter: List = [0]
 
-    def compile(self, elem) -> str:
+    def compile(self, elem, params=None) -> str:
+        if params:
+            cv_params.set(params)
+
         res = self._compile(elem)
         if self.root and self._subqueries:
             subq = ", ".join(f"\n  {k} AS ({v})" for k, v in self._subqueries.items())