cleaning up

src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php

@@ -527,10 +527,7 @@ public function setAttribute($key, $value)
         }
 
         if ($this->isJsonCastable($key) && ! is_null($value)) {
-            $value = $this->asJson($value);
-            if (false === $value) {
-                throw JsonEncodingException::forAttribute($key, json_last_error_msg());
-            }
+            $value = $this->castAttributeAsJson($key, $value);
         }
 
         // If this attribute contains a JSON ->, we'll set the proper value in the
@@ -613,6 +610,26 @@ protected function getArrayAttributeByKey($key)
                     $this->fromJson($this->attributes[$key]) : [];
     }
 
+    /**
+     * Cast the given attribute to JSON.
+     *
+     * @param  string  $key
+     * @param  mixed  $value
+     * @return string
+     */
+    protected function castAttributeAsJson($key, $value)
+    {
+        $value = $this->asJson($value);
+
+        if ($value === false) {
+            throw JsonEncodingException::forAttribute(
+                $this, $key, json_last_error_msg()
+            );
+        }
+
+        return $value;
+    }
+
     /**
      * Encode the given value as JSON.
      *

src/Illuminate/Database/Eloquent/JsonEncodingException.php

@@ -21,12 +21,15 @@ public static function forModel($model, $message)
     /**
      * Create a new JSON encoding exception for an attribute.
      *
+     * @param  mixed  $model
      * @param  mixed  $key
      * @param  string $message
      * @return static
      */
-    public static function forAttribute($key, $message)
+    public static function forAttribute($model, $key, $message)
     {
-        return new static('Error encoding value of attribute ['.$key.'] to JSON: '.$message);
+        $class = get_class($model);
+
+        return new static("Unable to encode attribute [{$key}] for model [{$class}] to JSON: {$message}.");
     }
 }

tests/Database/DatabaseEloquentModelTest.php

@@ -1468,7 +1468,6 @@ public function testModelAttributeCastingPreservesNull()
 
     /**
      * @expectedException \Illuminate\Database\Eloquent\JsonEncodingException
-     * @expectedExceptionMessage Error encoding value of attribute
      */
     public function testModelAttributeCastingFailsOnUnencodableData()
     {