diff --git a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/AllTypesEntity.php b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/AllTypesEntity.php
new file mode 100644
index 0000000000000..f47b948a70202
--- /dev/null
+++ b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/AllTypesEntity.php
@@ -0,0 +1,159 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bridge\Doctrine\Tests\Fixtures;
+
+use Doctrine\DBAL\Types\Types;
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\Common\Collections\ArrayCollection;
+use Doctrine\Common\Collections\Collection;
+
+#[ORM\Entity(repositoryClass: AllTypesEntityRepository::class)]
+class AllTypesEntity
+{
+    #[ORM\Id]
+    #[ORM\Column(type: Types::STRING)]
+    public string $id;
+
+    #[ORM\Column(type: Types::SMALLINT)]
+    public int $smallint;
+
+    #[ORM\Column(type: Types::INTEGER)]
+    public int $integer;
+
+    #[ORM\Column(type: Types::BIGINT, options: ['unsigned' => true])]
+    public string $bigint;
+
+    #[ORM\Column(type: Types::DECIMAL, precision: 10, scale: 2)]
+    public string $decimal;
+
+    #[ORM\Column(type: Types::SMALLFLOAT)]
+    public float $smallfloat;
+
+    #[ORM\Column(type: Types::FLOAT)]
+    public float $float;
+
+    #[ORM\Column(type: Types::STRING)]
+    public string $string;
+
+    #[ORM\Column(type: Types::ASCII_STRING)]
+    public string $asciiString;
+
+    #[ORM\Column(type: Types::TEXT)]
+    public string $text;
+
+    #[ORM\Column(type: Types::GUID)]
+    public string $guid;
+
+    #[ORM\Column(type: Types::ENUM)]
+    public EntityEnum $enum;
+
+    #[ORM\Column(type: Types::BINARY)]
+    public mixed $binaryAsResource;
+
+    #[ORM\Column(type: Types::BLOB)]
+    public mixed $blobAsResource;
+
+    #[ORM\Column(type: Types::BOOLEAN)]
+    public bool $boolean;
+
+    #[ORM\Column(type: Types::DATE_MUTABLE)]
+    public \DateTime $date;
+
+    #[ORM\Column(type: Types::DATE_IMMUTABLE)]
+    public \DateTimeImmutable $dateImmutable;
+
+    #[ORM\Column(type: Types::DATETIME_MUTABLE)]
+    public \DateTime $datetime;
+
+    #[ORM\Column(type: Types::DATETIME_IMMUTABLE)]
+    public \DateTimeImmutable $datetimeImmutable;
+
+    #[ORM\Column(type: Types::DATETIMETZ_MUTABLE)]
+    public \DateTime $datetimetz;
+
+    #[ORM\Column(type: Types::DATETIMETZ_IMMUTABLE)]
+    public \DateTimeImmutable $datetimetzImmutable;
+
+    #[ORM\Column(type: Types::TIME_MUTABLE)]
+    public \DateTime $time;
+
+    #[ORM\Column(type: Types::TIME_IMMUTABLE)]
+    public \DateTimeImmutable $timeImmutable;
+
+    #[ORM\Column(type: Types::DATEINTERVAL)]
+    public \DateInterval $dateinterval;
+
+    #[ORM\ManyToOne(targetEntity: RelatedEntity::class)]
+    #[ORM\JoinColumn(name: 'many_to_one_id', referencedColumnName: 'id')]
+    public RelatedEntity $manyToOne;
+
+    #[ORM\OneToOne(targetEntity: RelatedEntity::class)]
+    #[ORM\JoinColumn(name: 'one_to_one_id', referencedColumnName: 'id')]
+    public RelatedEntity $oneToOne;
+
+    #[ORM\Column(type: Types::SIMPLE_ARRAY)]
+    public array $simpleArray;
+
+    #[ORM\Column(type: Types::JSON, nullable: true)]
+    public mixed $json = [];
+
+    #[ORM\OneToMany(targetEntity: RelatedEntity::class, mappedBy: 'allEntity')]
+    public Collection $oneToMany;
+
+    #[ORM\ManyToMany(targetEntity: RelatedEntity::class)]
+    #[ORM\JoinTable(name: 'allentity_related')]
+    public Collection $manyToMany;
+
+    public function __construct(RelatedEntity $related)
+    {
+        $this->id = '1';
+        $this->smallint = 1;
+        $this->integer = 42;
+        $this->bigint = PHP_INT_MAX;
+        $this->decimal = '1234.56';
+        $this->smallfloat = 1.23;
+        $this->float = 3.1415;
+        $this->string = 'Iñtërńâtiônàlizætiøn';
+        $this->asciiString = 'ASCII text';
+        $this->text = 'This is a large text block.';
+        $this->guid = '4bb4f8f5-ea8d-4000-abf7-bb5b07dc2322';
+        $this->enum = EntityEnum::VALUE;
+
+        $this->binaryAsResource = fopen('php://memory', 'r+');
+        fwrite($this->binaryAsResource, 'binary data');
+        rewind($this->binaryAsResource);
+
+        $this->blobAsResource = fopen('php://memory', 'r+');
+        fwrite($this->blobAsResource, 'blob data');
+        rewind($this->blobAsResource);
+
+        $this->boolean = true;
+        $this->date = new \DateTime('2025-01-01');
+        $this->dateImmutable = new \DateTimeImmutable('2025-01-01');
+        $this->datetime = new \DateTime('2025-01-01 12:34:56');
+        $this->datetimeImmutable = new \DateTimeImmutable('2025-01-01 12:34:56');
+        $this->datetimetz = new \DateTime('2025-01-01 12:00:00', new \DateTimeZone('UTC'));
+        $this->datetimetzImmutable = new \DateTimeImmutable('2025-01-01 12:34:56', new \DateTimeZone('UTC'));
+        $this->time = new \DateTime('12:34:56');
+        $this->timeImmutable = new \DateTimeImmutable('12:34:56');
+        $this->dateinterval = new \DateInterval('P2D');
+
+        $this->manyToOne = $related;
+        $this->oneToOne = $related;
+
+        $this->simpleArray = ['foo', 'bar'];
+        $this->json = ['key' => 'value', 'list' => [1, 2, 3]];
+
+        $this->oneToMany = new ArrayCollection([$related]);
+        $this->manyToMany = new ArrayCollection([$related]);
+    }
+}
diff --git a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/AllTypesEntityRepository.php b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/AllTypesEntityRepository.php
new file mode 100644
index 0000000000000..b1383bf93998f
--- /dev/null
+++ b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/AllTypesEntityRepository.php
@@ -0,0 +1,24 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bridge\Doctrine\Tests\Fixtures;
+
+use Doctrine\ORM\EntityRepository;
+
+class AllTypesEntityRepository extends EntityRepository
+{
+    public ?AllTypesEntity $result = null;
+
+    public function findByCustom(): ?AllTypesEntity
+    {
+        return $this->result;
+    }
+}
diff --git a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/EntityEnum.php b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/EntityEnum.php
new file mode 100644
index 0000000000000..8ba4b07a60750
--- /dev/null
+++ b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/EntityEnum.php
@@ -0,0 +1,17 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bridge\Doctrine\Tests\Fixtures;
+
+enum EntityEnum: string
+{
+    case VALUE = 'value';
+}
diff --git a/src/Symfony/Bridge/Doctrine/Tests/Fixtures/RelatedEntity.php b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/RelatedEntity.php
new file mode 100644
index 0000000000000..12f3334c3dabb
--- /dev/null
+++ b/src/Symfony/Bridge/Doctrine/Tests/Fixtures/RelatedEntity.php
@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bridge\Doctrine\Tests\Fixtures;
+
+use Doctrine\ORM\Mapping as ORM;
+
+#[ORM\Entity]
+class RelatedEntity
+{
+    #[ORM\Id]
+    #[ORM\GeneratedValue]
+    #[ORM\Column(type: 'integer')]
+    public int $id;
+
+    #[ORM\Column(type: 'string', length: 255)]
+    public string $name = 'Related';
+}
diff --git a/src/Symfony/Bridge/Doctrine/Tests/Validator/Constraints/UniqueEntityValidatorTest.php b/src/Symfony/Bridge/Doctrine/Tests/Validator/Constraints/UniqueEntityValidatorTest.php
index 4f93768cddf7c..a0a0045097024 100644
--- a/src/Symfony/Bridge/Doctrine/Tests/Validator/Constraints/UniqueEntityValidatorTest.php
+++ b/src/Symfony/Bridge/Doctrine/Tests/Validator/Constraints/UniqueEntityValidatorTest.php
@@ -19,6 +19,7 @@
 use Doctrine\Persistence\ObjectManager;
 use PHPUnit\Framework\MockObject\MockObject;
 use Symfony\Bridge\Doctrine\Tests\DoctrineTestHelper;
+use Symfony\Bridge\Doctrine\Tests\Fixtures\AllTypesEntity;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\AssociatedEntityDto;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\AssociationEntity;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\AssociationEntity2;
@@ -31,6 +32,7 @@
 use Symfony\Bridge\Doctrine\Tests\Fixtures\Employee;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\HireAnEmployee;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\Person;
+use Symfony\Bridge\Doctrine\Tests\Fixtures\RelatedEntity;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\SingleIntIdEntity;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\SingleIntIdNoToStringEntity;
 use Symfony\Bridge\Doctrine\Tests\Fixtures\SingleIntIdStringWrapperNameEntity;
@@ -120,6 +122,8 @@ private function createSchema($em)
             $em->getClassMetadata(CompositeObjectNoToStringIdEntity::class),
             $em->getClassMetadata(SingleIntIdStringWrapperNameEntity::class),
             $em->getClassMetadata(UserUuidNameEntity::class),
+            $em->getClassMetadata(AllTypesEntity::class),
+            $em->getClassMetadata(RelatedEntity::class),
         ]);
     }
 
@@ -1448,4 +1452,199 @@ public function testUuidIdentifierWithSameValueDifferentInstanceDoesNotCauseViol
 
         $this->assertNoViolation();
     }
+
+    /**
+     * @dataProvider provideFieldTypes
+     */
+    public function testValidateTypesUniqueness(string $field)
+    {
+        $related = new RelatedEntity();
+        $this->em->persist($related);
+        $entity = new AllTypesEntity($related);
+        $this->em->persist($entity);
+        $this->em->flush();
+
+        $entity2 = new AllTypesEntity($related);
+
+        $constraint = new UniqueEntity(
+            fields: $field,
+            em: self::EM_NAME,
+            entityClass: AllTypesEntity::class,
+        );
+
+        $this->validator->validate($entity2, $constraint);
+
+        $this->assertCount(1, $this->context->getViolations());
+    }
+
+    /**
+     * @dataProvider provideFieldTypes
+     *
+     * @group legacy
+     */
+    public function testValidateTypesUniquenessDoctrineStyle(string $field)
+    {
+        $related = new RelatedEntity();
+        $this->em->persist($related);
+        $entity = new AllTypesEntity($related);
+        $this->em->persist($entity);
+        $this->em->flush();
+
+        $entity2 = new AllTypesEntity($related);
+
+        $constraint = new UniqueEntity([
+            'fields' => [$field],
+            'em' => self::EM_NAME,
+            'entityClass' => AllTypesEntity::class,
+        ]);
+
+        $this->validator->validate($entity2, $constraint);
+
+        $this->assertCount(1, $this->context->getViolations());
+    }
+
+    public static function provideFieldTypes(): \Generator
+    {
+        yield ['smallint'];
+        yield ['integer'];
+        yield ['bigint'];
+        yield ['decimal'];
+        yield ['smallfloat'];
+        yield ['float'];
+        yield ['string'];
+        yield ['asciiString'];
+        yield ['text'];
+        yield ['guid'];
+        yield ['enum'];
+        yield ['binaryAsResource'];
+        yield ['blobAsResource'];
+        yield ['boolean'];
+        yield ['date'];
+        yield ['dateImmutable'];
+        yield ['datetime'];
+        yield ['datetimeImmutable'];
+        yield ['datetimetz'];
+        yield ['datetimetzImmutable'];
+        yield ['time'];
+        yield ['timeImmutable'];
+        yield ['dateinterval'];
+        yield ['manyToOne'];
+        yield ['oneToOne'];
+    }
+
+    /**
+     * @dataProvider provideUnsupportedByFindByMethodFieldTypesAndAssociations
+     */
+    public function testUnsupportedTypesWithoutCustomMethodThrowException(string $field, string $error)
+    {
+        $this->expectException(ConstraintDefinitionException::class);
+        $this->expectExceptionMessage($error);
+
+        $related = new RelatedEntity();
+        $entity = new AllTypesEntity($related);
+
+        $constraint = new UniqueEntity(
+            fields: $field,
+            em: self::EM_NAME,
+            entityClass: AllTypesEntity::class,
+        );
+
+        $this->validator->validate($entity, $constraint);
+    }
+
+    /**
+     * @dataProvider provideUnsupportedByFindByMethodFieldTypesAndAssociations
+     *
+     * @group legacy
+     */
+    public function testUnsupportedTypesWithoutCustomMethodThrowExceptionDoctrineStyle(string $field, string $error)
+    {
+        $this->expectException(ConstraintDefinitionException::class);
+        $this->expectExceptionMessage($error);
+
+        $related = new RelatedEntity();
+        $entity = new AllTypesEntity($related);
+
+        $constraint = new UniqueEntity([
+            'fields' => [$field],
+            'em' => self::EM_NAME,
+            'entityClass' => AllTypesEntity::class,
+        ]);
+
+        $this->validator->validate($entity, $constraint);
+    }
+
+    /**
+     * @dataProvider provideUnsupportedByFindByMethodFieldTypesAndAssociations
+     */
+    public function testUnsupportedByFindByMethodTypesAndAssociationsDoesNotCauseViolation(string $field)
+    {
+        $related = new RelatedEntity();
+        $this->em->persist($related);
+        $entity1 = new AllTypesEntity($related);
+        $this->em->persist($entity1);
+        $this->em->flush();
+        $this->em->getRepository(AllTypesEntity::class)->result = $entity1;
+
+        $entity2 = new AllTypesEntity($related);
+
+        $constraint = new UniqueEntity(
+            fields: $field,
+            em: self::EM_NAME,
+            entityClass: AllTypesEntity::class,
+            repositoryMethod: 'findByCustom',
+        );
+
+        $this->validator->validate($entity2, $constraint);
+
+        $this->assertCount(1, $this->context->getViolations());
+    }
+
+    /**
+     * @dataProvider provideUnsupportedByFindByMethodFieldTypesAndAssociations
+     *
+     * @group legacy
+     */
+    public function testUnsupportedByFindByMethodTypesAndAssociationsDoesNotCauseViolationDoctrineStyle(string $field)
+    {
+        $related = new RelatedEntity();
+        $this->em->persist($related);
+        $entity1 = new AllTypesEntity($related);
+        $this->em->persist($entity1);
+        $this->em->flush();
+        $this->em->getRepository(AllTypesEntity::class)->result = $entity1;
+
+        $entity2 = new AllTypesEntity($related);
+
+        $constraint = new UniqueEntity([
+            'fields' => [$field],
+            'em' => self::EM_NAME,
+            'entityClass' => AllTypesEntity::class,
+            'repositoryMethod' => 'findByCustom',
+        ]);
+
+        $this->validator->validate($entity2, $constraint);
+
+        $this->assertCount(1, $this->context->getViolations());
+    }
+
+    public static function provideUnsupportedByFindByMethodFieldTypesAndAssociations(): \Generator
+    {
+        yield [
+            'simpleArray',
+            'The field "simpleArray" has a Doctrine type ("simple_array") that is not supported by the findBy method. You must define a custom repository method using the "repositoryMethod" option.',
+        ];
+        yield [
+            'json',
+            'The field "json" has a Doctrine type ("json") that is not supported by the findBy method. You must define a custom repository method using the "repositoryMethod" option.',
+        ];
+        yield [
+            'oneToMany',
+            'The field "oneToMany" is a Doctrine association of type "ONE_TO_MANY", which is not supported by the findBy method. You must define a custom repository method using the "repositoryMethod" option.',
+        ];
+        yield [
+            'manyToMany',
+            'The field "manyToMany" is a Doctrine association of type "MANY_TO_MANY", which is not supported by the findBy method. You must define a custom repository method using the "repositoryMethod" option.',
+        ];
+    }
 }
diff --git a/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php b/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
index eb2e89b94dfb8..dcea1468e0495 100644
--- a/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
+++ b/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
@@ -11,6 +11,8 @@
 
 namespace Symfony\Bridge\Doctrine\Validator\Constraints;
 
+use Doctrine\DBAL\Types\Types;
+use Doctrine\ORM\Mapping\ClassMetadata as MappingClassMetadata;
 use Doctrine\ORM\Mapping\MappingException as ORMMappingException;
 use Doctrine\Persistence\ManagerRegistry;
 use Doctrine\Persistence\Mapping\ClassMetadata;
@@ -106,6 +108,14 @@ public function validate(mixed $value, Constraint $constraint): void
             $criteria[$fieldName] = $fieldValue;
 
             if (\is_object($criteria[$fieldName]) && $class->hasAssociation($fieldName)) {
+                $associationMapping = [MappingClassMetadata::MANY_TO_MANY => 'MANY_TO_MANY', MappingClassMetadata::ONE_TO_MANY => 'ONE_TO_MANY'];
+                if (\in_array($class->getAssociationMapping($fieldName)['type'], [MappingClassMetadata::MANY_TO_MANY, MappingClassMetadata::ONE_TO_MANY], true)) {
+                    if ('findBy' === $constraint->repositoryMethod) {
+                        throw new ConstraintDefinitionException(\sprintf('The field "%s" is a Doctrine association of type "%s", which is not supported by the findBy method. You must define a custom repository method using the "repositoryMethod" option.', $fieldName, $associationMapping[$class->getAssociationMapping($fieldName)['type']]));
+                    } else {
+                        continue;
+                    }
+                }
                 /* Ensure the Proxy is initialized before using reflection to
                  * read its identifiers. This is necessary because the wrapped
                  * getter methods in the Proxy are being bypassed.
@@ -149,6 +159,12 @@ public function validate(mixed $value, Constraint $constraint): void
          * - One entity returned the uniqueness depends on the current entity.
          */
         if ('findBy' === $constraint->repositoryMethod) {
+            $metadata = $em->getClassMetadata($entityClass);
+            foreach ($criteria as $fieldName => $mapping) {
+                if (\in_array($metadata->getTypeOfField($fieldName), [Types::SIMPLE_ARRAY, Types::JSON], true)) {
+                    throw new ConstraintDefinitionException(\sprintf('The field "%s" has a Doctrine type ("%s") that is not supported by the findBy method. You must define a custom repository method using the "repositoryMethod" option.', $fieldName, $metadata->getTypeOfField($fieldName)));
+                }
+            }
             $arguments = [$criteria, null, 2];
         }