feat(query): Add ExistsQuery

AGENTS.md

@@ -54,6 +54,7 @@ Fluent, immutable, type-safe Elasticsearch query builder for PHP 8.4+. Zero prod
 ```
 QueryInterface ─┬─ TermQuery (uses BoostableQuery)
                 ├─ TermsQuery (uses BoostableQuery)
+                ├─ ExistsQuery (uses BoostableQuery)
                 ├─ MatchQuery (uses BoostableQuery, AnalyzerAwareQuery)
                 ├─ MatchPhraseQuery (uses BoostableQuery, AnalyzerAwareQuery)
                 ├─ BoolQuery (uses BoostableQuery)

README.md

@@ -111,6 +111,16 @@ use Bonu\ElasticsearchBuilder\Query\TermsQuery;
 new TermsQuery('status', ['active', 'pending'])->boost(5)
 ```
 
+### ExistsQuery
+
+https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-exists-query
+
+```php
+use Bonu\ElasticsearchBuilder\Query\ExistsQuery;
+
+new ExistsQuery('field')
+```
+
 ### MatchQuery
 
 https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-match-query

src/Query/AGENTS.md

@@ -16,6 +16,7 @@ Query classes implementing `QueryInterface`. All immutable; mutation methods clo
 | `MatchQuery.php` | Full-text match (OR/AND operators) | `BoostableQuery`, `AnalyzerAwareQuery` |
 | `MatchPhraseQuery.php` | Phrase match with optional slop | `BoostableQuery`, `AnalyzerAwareQuery` |
 | `BoolQuery.php` | must/should/mustNot/filter composition | `BoostableQuery` |
+| `ExistsQuery.php` | Field existence check | `BoostableQuery` |
 | `NestedQuery.php` | Query nested document paths | — |
 | `NumericRangeQuery.php` | Numeric gt/gte/lt/lte | extends `RangeQuery` |
 | `DatetimeRangeQuery.php` | Date gt/gte/lt/lte + format/timeZone | extends `RangeQuery` |

src/Query/ExistsQuery.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bonu\ElasticsearchBuilder\Query;
+
+/**
+ * @see https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-exists-query
+ */
+class ExistsQuery implements QueryInterface
+{
+    use BoostableQuery;
+
+    /**
+     * @param string|\Stringable $field
+     */
+    public function __construct(
+        protected string | \Stringable $field,
+    ) {
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function toArray(): array
+    {
+        return [
+            'exists' => $this->addBoostToQuery([
+                'field' => (string) $this->field,
+            ]),
+        ];
+    }
+}

tests/Integration/Query/ExistsQueryTest.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bonu\ElasticsearchBuilder\Tests\Integration\Query;
+
+use PHPUnit\Framework\Attributes\Test;
+use Bonu\ElasticsearchBuilder\QueryBuilder;
+use Bonu\ElasticsearchBuilder\Query\ExistsQuery;
+use Bonu\ElasticsearchBuilder\Tests\IntegrationTestCase;
+
+/**
+ * @internal
+ */
+final class ExistsQueryTest extends IntegrationTestCase
+{
+    #[Test]
+    public function itFiltersDocumentsWhereFieldExists(): void
+    {
+        $response = $this->client?->search(
+            new QueryBuilder(self::INDEX)
+                ->query(new ExistsQuery('track_id'))
+                ->build()
+        )->asArray();
+
+        $this->assertGreaterThan(0, $response['hits']['total']['value']);
+    }
+}

tests/Unit/Query/ExistsQueryTest.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bonu\ElasticsearchBuilder\Tests\Unit\Query;
+
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\Attributes\Depends;
+use Bonu\ElasticsearchBuilder\Tests\TestCase;
+use Bonu\ElasticsearchBuilder\Query\ExistsQuery;
+
+use const PHP_FLOAT_EPSILON;
+
+/**
+ * @internal
+ */
+final class ExistsQueryTest extends TestCase
+{
+    #[Test]
+    public function itCorrectlyBuildsArray(): void
+    {
+        $array = new ExistsQuery('user')->toArray();
+
+        $this->assertSame([
+            'exists' => [
+                'field' => 'user',
+                'boost' => 1.0,
+            ],
+        ], $array);
+    }
+
+    #[Depends('itCorrectlyBuildsArray')]
+    #[Test]
+    public function itCorrectlySetsBoost(): void
+    {
+        $array = new ExistsQuery('user')->boost(10.0)->toArray();
+
+        $this->assertEqualsWithDelta(10.0, $array['exists']['boost'], PHP_FLOAT_EPSILON);
+    }
+}