From 189592c77980e766f92f6eb77dbd7412db106086 Mon Sep 17 00:00:00 2001
From: Patrick Molgaard <draaglom@gmail.com>
Date: Fri, 20 May 2022 13:04:25 +0100
Subject: [PATCH] perf: don't recompile escapeRegExp for every query (#8956)

Context: the query builder is pretty CPU intensive, and can be slow -
e.g. https://github.com/typeorm/typeorm/issues/3857

One of the things which makes this slow is `escapeRegExp` in the query
builder: we freshly construct the same RegExp once per
`replacePropertyName` invocation (many times per overall query!) and
since the RegExp itself is constant -- we can lift it out and construct
it once.

Over-all this saves about 8% on our query build times as measured by
 #8955.
---
 src/query-builder/QueryBuilder.ts | 7 ++-----
 src/util/escapeRegExp.ts          | 4 ++++
 2 files changed, 6 insertions(+), 5 deletions(-)
 create mode 100644 src/util/escapeRegExp.ts

diff --git a/src/query-builder/QueryBuilder.ts b/src/query-builder/QueryBuilder.ts
index c23f8cd376..c8d378b69f 100644
--- a/src/query-builder/QueryBuilder.ts
+++ b/src/query-builder/QueryBuilder.ts
@@ -24,6 +24,7 @@ import { EntityPropertyNotFoundError } from "../error/EntityPropertyNotFoundErro
 import { ReturningType } from "../driver/Driver"
 import { OracleDriver } from "../driver/oracle/OracleDriver"
 import { InstanceChecker } from "../util/InstanceChecker"
+import { escapeRegExp } from "../util/escapeRegExp"
 
 // todo: completely cover query builder with tests
 // todo: entityOrProperty can be target name. implement proper behaviour if it is.
@@ -701,12 +702,8 @@ export abstract class QueryBuilder<Entity> {
     /**
      * Replaces all entity's propertyName to name in the given statement.
      */
-    protected replacePropertyNames(statement: string) {
-        // Escape special characters in regular expressions
-        // Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Escaping
-        const escapeRegExp = (s: String) =>
-            s.replace(/[.*+\-?^${}()|[\]\\]/g, "\\$&")
 
+    protected replacePropertyNames(statement: string) {
         for (const alias of this.expressionMap.aliases) {
             if (!alias.hasMetadata) continue
             const replaceAliasNamePrefix = this.expressionMap
diff --git a/src/util/escapeRegExp.ts b/src/util/escapeRegExp.ts
new file mode 100644
index 0000000000..05597f8a49
--- /dev/null
+++ b/src/util/escapeRegExp.ts
@@ -0,0 +1,4 @@
+// Escape special characters in regular expressions
+// Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Escaping
+const ESCAPE_REGEXP = /[.*+\-?^${}()|[\]\\]/g
+export const escapeRegExp = (s: String) => s.replace(ESCAPE_REGEXP, "\\$&")