Auto-generate check constraint name when name is empty

src/Db/Adapter/MysqlAdapter.php

@@ -1121,7 +1121,7 @@ protected function getCheckConstraints(string $tableName): array
     protected function getAddCheckConstraintInstructions(TableMetadata $table, CheckConstraint $checkConstraint): AlterInstructions
     {
         $constraintName = $checkConstraint->getName();
-        if ($constraintName === null) {
+        if ($constraintName === null || $constraintName === '') {
             // Auto-generate constraint name if not provided
             $constraintName = $table->getName() . '_chk_' . substr(md5($checkConstraint->getExpression()), 0, 8);
         }

src/Db/Adapter/PostgresAdapter.php

@@ -826,7 +826,7 @@ protected function getCheckConstraints(string $tableName): array
     protected function getAddCheckConstraintInstructions(TableMetadata $table, CheckConstraint $checkConstraint): AlterInstructions
     {
         $constraintName = $checkConstraint->getName();
-        if ($constraintName === null) {
+        if ($constraintName === null || $constraintName === '') {
             // Auto-generate constraint name if not provided
             $parts = $this->getSchemaName($table->getName());
             $constraintName = $parts['table'] . '_chk_' . substr(md5($checkConstraint->getExpression()), 0, 8);

src/Db/Adapter/SqliteAdapter.php

@@ -1546,7 +1546,7 @@ protected function getAddCheckConstraintInstructions(TableMetadata $table, Check
 
         $instructions->addPostStep(function (array $state) use ($checkConstraint): array {
             $constraintName = $checkConstraint->getName();
-            if ($constraintName === null) {
+            if ($constraintName === null || $constraintName === '') {
                 // Auto-generate constraint name if not provided
                 $constraintName = 'chk_' . substr(md5($checkConstraint->getExpression()), 0, 8);
             }

tests/TestCase/Db/Adapter/MysqlAdapterTest.php

@@ -2677,8 +2677,10 @@ public function testAddCheckConstraintWithAutoGeneratedName(): void
         $dialect = $driver->schemaDialect();
         $constraints = $dialect->describeCheckConstraints('check_table2');
         $this->assertCount(1, $constraints);
-        $expected = $driver->isMariaDb() ? 'CONSTRAINT_1' : 'check_table2_chk_';
-        $this->assertStringContainsString($expected, $constraints[0]['name']);
+        // The name is generated by migrations (not left to the DB), so it is
+        // identical on MySQL and MariaDB instead of the DB fallback CONSTRAINT_1.
+        $expectedName = 'check_table2_chk_' . substr(md5('age >= 18'), 0, 8);
+        $this->assertSame($expectedName, $constraints[0]['name']);
     }
 
     public function testHasCheckConstraint(): void

tests/TestCase/Db/Adapter/PostgresAdapterTest.php

@@ -2950,6 +2950,21 @@ public function testAddCheckConstraint(): void
         $this->assertTrue($this->adapter->hasCheckConstraint('check_table', 'price_positive'));
     }
 
+    public function testAddCheckConstraintAutoGeneratesName(): void
+    {
+        $table = new Table('check_table_auto', [], $this->adapter);
+        $table->addColumn('quantity', 'integer')
+              ->create();
+
+        $expression = 'quantity >= 0';
+        // An empty name must trigger auto-generation, not emit invalid `ADD CONSTRAINT CHECK`.
+        $checkConstraint = new CheckConstraint('', $expression);
+        $this->adapter->addCheckConstraint($table->getTable(), $checkConstraint);
+
+        $expectedName = 'check_table_auto_chk_' . substr(md5($expression), 0, 8);
+        $this->assertTrue($this->adapter->hasCheckConstraint('check_table_auto', $expectedName));
+    }
+
     public function testHasCheckConstraint(): void
     {
         $table = new Table('check_table3', [], $this->adapter);

tests/TestCase/Db/Adapter/SqliteAdapterTest.php

@@ -3173,6 +3173,21 @@ public function testAddCheckConstraint(): void
         $this->assertTrue($this->adapter->hasCheckConstraint('check_table', 'price_positive'));
     }
 
+    public function testAddCheckConstraintAutoGeneratesName(): void
+    {
+        $table = new Table('check_table_auto', [], $this->adapter);
+        $table->addColumn('quantity', 'integer')
+              ->create();
+
+        $expression = 'quantity >= 0';
+        // An empty name must trigger auto-generation, not produce an unnamed constraint.
+        $checkConstraint = new CheckConstraint('', $expression);
+        $this->adapter->addCheckConstraint($table->getTable(), $checkConstraint);
+
+        $expectedName = 'chk_' . substr(md5($expression), 0, 8);
+        $this->assertTrue($this->adapter->hasCheckConstraint('check_table_auto', $expectedName));
+    }
+
     public function testHasCheckConstraint(): void
     {
         $table = new Table('check_table3', [], $this->adapter);