Add EXISTS and NOT EXISTS to SELECT queries

src/Expression/CallbackExpr.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace RebelCode\Atlas\Expression;
+
+/** Renders using a callback. */
+class CallbackExpr extends BaseExpr
+{
+    /** @var callable():string */
+    private $callback;
+
+    /**
+     * Creates a new callback expression.
+     * @param callable():string $callback A function that renders the expr SQL.
+     */
+    public function __construct(callable $callback)
+    {
+        $this->callback = $callback;
+    }
+
+    /** @inheritdoc */
+    protected function toBaseString(): string
+    {
+        return call_user_func($this->callback);
+    }
+}

src/Query/SelectQuery.php

@@ -5,8 +5,10 @@
 use RebelCode\Atlas\DatabaseAdapter;
 use RebelCode\Atlas\DataSource;
 use RebelCode\Atlas\Exception\QuerySqlException;
+use RebelCode\Atlas\Expression\CallbackExpr;
 use RebelCode\Atlas\Expression\ColumnTerm;
 use RebelCode\Atlas\Expression\ExprInterface;
+use RebelCode\Atlas\Expression\FnExpr;
 use RebelCode\Atlas\Expression\Term;
 use RebelCode\Atlas\Order;
 use RebelCode\Atlas\Query;
@@ -128,6 +130,20 @@ public function getAlias(): ?string
         return $this->alias;
     }
 
+    public function exists(): ExprInterface
+    {
+        return new FnExpr('EXISTS', [
+            new CallbackExpr(fn () => $this->toSql()),
+        ]);
+    }
+
+    public function notExists(): ExprInterface
+    {
+        return new FnExpr('NOT EXISTS', [
+            new CallbackExpr(fn () => $this->toSql()),
+        ]);
+    }
+
     /** @inheritDoc */
     public function toSql(): string
     {

tests/Expression/CallbackExprTest.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace RebelCode\Atlas\Test\Expression;
+
+use PHPUnit\Framework\TestCase;
+use RebelCode\Atlas\Expression\CallbackExpr;
+
+class CallbackExprTest extends TestCase
+{
+    public function testRenderClosure()
+    {
+        $closure = new CallbackExpr(function () {
+            return 'foobar';
+        });
+
+        $this->assertEquals('foobar', $closure->toSql());
+    }
+
+    public function testRenderArrowFn()
+    {
+        $var = 'foobar';
+        $closure = new CallbackExpr(fn () => $var);
+
+        $this->assertEquals('foobar', $closure->toSql());
+    }
+}

tests/Query/SelectQueryTest.php

@@ -14,6 +14,9 @@
 use RebelCode\Atlas\Query\SelectQuery;
 use RebelCode\Atlas\Test\Helpers\ReflectionHelper;
 
+use function RebelCode\Atlas\col;
+use function RebelCode\Atlas\table;
+
 class SelectQueryTest extends TestCase
 {
     use ReflectionHelper;
@@ -446,4 +449,22 @@ public function testCompileSelectEverything()
 
         $this->assertEquals($expected, $actual);
     }
+
+    public function testExists()
+    {
+        $query = new SelectQuery();
+        $query = $query->from(table('test'))->where(col('role')->eq('admin'));
+        $exists = $query->exists();
+
+        $this->assertEquals("EXISTS(SELECT * FROM `test` WHERE (`role` = 'admin'))", $exists->toSql());
+    }
+
+    public function testNotExists()
+    {
+        $query = new SelectQuery();
+        $query = $query->from(table('test'))->where(col('role')->eq('admin'));
+        $exists = $query->notExists();
+
+        $this->assertEquals("NOT EXISTS(SELECT * FROM `test` WHERE (`role` = 'admin'))", $exists->toSql());
+    }
 }