Add a "defaultValue" to the resolver builder. (#941)

Author: pmelab

src/GraphQL/Resolver/DefaultValue.php

@@ -0,0 +1,72 @@
+<?php
+
+namespace Drupal\graphql\GraphQL\Resolver;
+
+use Drupal\graphql\GraphQL\Execution\FieldContext;
+use Drupal\graphql\GraphQL\Execution\ResolveContext;
+use Drupal\graphql\GraphQL\Utility\DeferredUtility;
+use GraphQL\Deferred;
+use GraphQL\Type\Definition\ResolveInfo;
+
+/**
+ * Default value resolver.
+ *
+ * Allows to fall back if a value is NULL.
+ */
+class DefaultValue implements ResolverInterface {
+
+  /**
+   * The initial value.
+   *
+   * @var \Drupal\graphql\GraphQL\Resolver\ResolverInterface
+   */
+  protected $value;
+
+  /**
+   * The fallback value in case the initial value resolves to NULL.
+   *
+   * @var \Drupal\graphql\GraphQL\Resolver\ResolverInterface
+   */
+  protected $default;
+
+
+  /**
+   * DefaultValue constructor.
+   *
+   * @param \Drupal\graphql\GraphQL\Resolver\ResolverInterface $value
+   *   The initial value to check.
+   * @param \Drupal\graphql\GraphQL\Resolver\ResolverInterface $default
+   *   The fallback value returned if the initial one resolves to NULL.
+   */
+  public function __construct(ResolverInterface $value, ResolverInterface $default) {
+    $this->value = $value;
+    $this->default = $default;
+  }
+
+
+  /**
+   * {@inheritDoc}
+   */
+  public function resolve(
+    $value,
+    $args,
+    ResolveContext $context,
+    ResolveInfo $info,
+    FieldContext $field
+  ) {
+    $result = $this->value->resolve($value, $args, $context, $info, $field);
+    if ($result === NULL) {
+      return $this->default->resolve($value, $args, $context, $info, $field);
+    }
+
+    if ($result instanceof Deferred) {
+      return DeferredUtility::returnFinally($result, function ($current) use ($value, $args, $context, $info, $field) {
+        if ($current === NULL) {
+          return $this->default->resolve($value, $args, $context, $info, $field);
+        }
+        return $current;
+      });
+    }
+    return $result;
+  }
+}

src/GraphQL/ResolverBuilder.php

@@ -8,6 +8,7 @@
 use Drupal\graphql\GraphQL\Resolver\Composite;
 use Drupal\graphql\GraphQL\Resolver\Condition;
 use Drupal\graphql\GraphQL\Resolver\Context;
+use Drupal\graphql\GraphQL\Resolver\DefaultValue;
 use Drupal\graphql\GraphQL\Resolver\Map;
 use Drupal\graphql\GraphQL\Resolver\ParentValue;
 use Drupal\graphql\GraphQL\Resolver\Path;
@@ -134,4 +135,14 @@ public function fromContext($name, $default = NULL) {
     return new Context($name, $default);
   }
 
+  /**
+   * @param $value
+   * @param $default
+   *
+   * @return \Drupal\graphql\GraphQL\Resolver\DefaultValue
+   */
+  public function defaultValue($value, $default) {
+    return new DefaultValue($value, $default);
+  }
+
 }

tests/src/Kernel/ResolverBuilderTest.php

@@ -195,6 +195,28 @@ public function testCompose() {
     $this->assertResults($query, [], ['tree' => ['name' => 'SOME TREE NAME']]);
   }
 
+  /**
+   * @covers ::compose
+   */
+  public function testComposeNullValue() {
+    $this->mockResolver('Query', 'tree', $this->builder->fromValue(['name' => 'some tree', 'id' => 5]));
+    $this->mockResolver('Tree', 'name', $this->builder->compose(
+      $this->builder->fromValue(NULL),
+      $this->builder->produce('uppercase')
+        ->map('string', $this->builder->fromParent())
+    ));
+
+    $query = <<<GQL
+      query {
+        tree {
+          name
+        }
+      }
+GQL;
+
+    $this->assertResults($query, [], ['tree' => ['name' => NULL]]);
+  }
+
   /**
    * @covers ::context
    * @covers ::fromContext
@@ -287,5 +309,105 @@ public function testParentCond() {
 
     $this->assertResults($query, [], ['tree' => ['name' => 'But this should.']]);
   }
+
+  /**
+   * @covers ::defaultValue
+   */
+  public function testSimpleDefaultValue() {
+    $this->mockResolver('Query', 'tree', ['name' => 'some tree', 'id' => 5]);
+    $this->mockResolver('Tree', 'name', $this->builder->defaultValue(
+      $this->builder->fromValue(NULL),
+      $this->builder->fromValue('bar')
+    ));
+
+    $this->mockResolver('Tree', 'uri', $this->builder->defaultValue(
+      $this->builder->fromValue('baz'),
+      $this->builder->fromValue('bar')
+    ));
+
+    $query = <<<GQL
+      query {
+        tree(id: 1) {
+          name
+          uri
+        }
+      }
+GQL;
+
+    $this->assertResults($query, [], [
+      'tree' => [
+        'name' => 'bar',
+        'uri' => 'baz',
+      ]
+    ]);
+  }
+
+  public function testCompositeDefaultValue() {
+
+    $this->mockResolver('Query', 'tree', ['name' => 'some tree', 'id' => 5]);
+    $this->mockResolver('Tree', 'name', $this->builder->defaultValue(
+      $this->builder->compose(
+        $this->builder->fromValue('baz'),
+        $this->builder->fromValue(NULL)
+      ),
+      $this->builder->fromValue('bar')
+    ));
+
+    $this->mockResolver('Tree', 'uri', $this->builder->defaultValue(
+      $this->builder->compose(
+        $this->builder->fromValue(TRUE),
+        $this->builder->fromValue('baz')
+      ),
+      $this->builder->fromValue('bar')
+    ));
+
+    $query = <<<GQL
+      query {
+        tree(id: 1) {
+          name
+          uri
+        }
+      }
+GQL;
+
+    $this->assertResults($query, [], [
+      'tree' => [
+        'name' => 'bar',
+        'uri' => 'baz',
+      ]
+    ]);
+  }
+
+  /**
+   * @covers ::defaultValue
+   */
+  public function testDeferredDefaultValue() {
+    $this->mockResolver('Query', 'tree', ['name' => 'some tree', 'id' => 5]);
+    $this->mockResolver('Tree', 'name', $this->builder->defaultValue(
+      $this->builder->callback(function () { return new Deferred(function () { return NULL; }); }),
+      $this->builder->callback(function () { return new Deferred(function () { return 'bar'; }); })
+    ));
+
+    $this->mockResolver('Tree', 'uri', $this->builder->defaultValue(
+      $this->builder->callback(function () { return new Deferred(function () { return 'baz'; }); }),
+      $this->builder->callback(function () { return new Deferred(function () { return 'bar'; }); })
+    ));
+
+    $query = <<<GQL
+      query {
+        tree(id: 1) {
+          name
+          uri
+        }
+      }
+GQL;
+
+    $this->assertResults($query, [], [
+      'tree' => [
+        'name' => 'bar',
+        'uri' => 'baz',
+      ]
+    ]);
+  }
 }