From 208da58bbd8ccc6f5076d7e80071ef0ba970bc22 Mon Sep 17 00:00:00 2001
From: jmarkerink <jmarkerink@outlook.com>
Date: Mon, 29 Sep 2025 17:41:22 +0200
Subject: [PATCH] feat: added isNumber expression type operator

---
 .../mongo/backend/aggregation/Expression.java        | 12 ++++++++++++
 .../mongo/backend/aggregation/ExpressionTest.java    | 12 ++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/core/src/main/java/de/bwaldvogel/mongo/backend/aggregation/Expression.java b/core/src/main/java/de/bwaldvogel/mongo/backend/aggregation/Expression.java
index 404c5f07..d5b81399 100644
--- a/core/src/main/java/de/bwaldvogel/mongo/backend/aggregation/Expression.java
+++ b/core/src/main/java/de/bwaldvogel/mongo/backend/aggregation/Expression.java
@@ -43,6 +43,7 @@
 import de.bwaldvogel.mongo.backend.NumericUtils;
 import de.bwaldvogel.mongo.backend.Utils;
 import de.bwaldvogel.mongo.backend.ValueComparator;
+import de.bwaldvogel.mongo.bson.Decimal128;
 import de.bwaldvogel.mongo.bson.Document;
 import de.bwaldvogel.mongo.bson.ObjectId;
 import de.bwaldvogel.mongo.exception.BadValueException;
@@ -772,6 +773,17 @@ Object apply(List<?> expressionValue, Document document) {
         }
     },
 
+    $isNumber {
+        @Override
+        Boolean apply(List<?> expressionValue, Document document) {
+            Object value = requireSingleValue(expressionValue);
+            return (value instanceof Integer ||
+                value instanceof Decimal128 ||
+                value instanceof Double ||
+                value instanceof Long);
+        }
+    },
+
     $literal {
         @Override
         Object apply(Object expressionValue, Document document) {
diff --git a/core/src/test/java/de/bwaldvogel/mongo/backend/aggregation/ExpressionTest.java b/core/src/test/java/de/bwaldvogel/mongo/backend/aggregation/ExpressionTest.java
index 0a9b5415..093890cb 100644
--- a/core/src/test/java/de/bwaldvogel/mongo/backend/aggregation/ExpressionTest.java
+++ b/core/src/test/java/de/bwaldvogel/mongo/backend/aggregation/ExpressionTest.java
@@ -1781,6 +1781,18 @@ void testEvaluateIsArray() throws Exception {
             .withMessage("[Error 16020] Expression $isArray takes exactly 1 arguments. 2 were passed in.");
     }
 
+    @Test
+    void testEvaluateIsNumber() throws Exception {
+        assertThat(Expression.evaluate(json("$isNumber: ['hello']"), json(""))).isEqualTo(false);
+        assertThat(Expression.evaluate(json("$isNumber: 'pi'}"), json(""))).isEqualTo(false);
+        assertThat(Expression.evaluate(json("$isNumber: null"), json(""))).isEqualTo(false);
+        assertThat(Expression.evaluate(json("$isNumber: '$value'"), json("value: 'a'"))).isEqualTo(false);
+        assertThat(Expression.evaluate(json("$isNumber: '$value'"), json("value: ['abc']"))).isEqualTo(false);
+        assertThat(Expression.evaluate(json("$isNumber: '$value'"), json("value: 1"))).isEqualTo(true);
+        assertThat(Expression.evaluate(json("$isNumber: '$value'"), json("value: 2.0"))).isEqualTo(true);
+        assertThat(Expression.evaluate(json("$isNumber: '$value'"), json("value: 3.141592653589793"))).isEqualTo(true);
+    }
+
     @Test
     void testEvaluateLiteral() throws Exception {
         assertThat(Expression.evaluate(json("$literal: {$add: [2, 3]}"), json(""))).isEqualTo(json("$add: [2, 3]"));