Update Laravel Excel docs with upsert columns explanation

3.1/imports/concerns.md

@@ -23,6 +23,8 @@ pageClass: no-toc
 |`Maatwebsite\Excel\Concerns\WithCustomCsvSettings`| Allows to run custom Csv settings for this specific importable. | [Custom CSV Settings](/3.1/imports/custom-csv-settings.html) |
 |`Maatwebsite\Excel\Concerns\WithStartRow`| Define a custom start row. | |
 |`Maatwebsite\Excel\Concerns\WithProgressBar`| Shows a progress bar when uploading via the console. | [Progress Bar](/3.1/imports/progress-bar.html) |
+|`Maatwebsite\Excel\Concerns\WithUpsert`| Allows to upsert models. | [Upserting models](/3.1/imports/model.html#upserting-models) |
+|`Maatwebsite\Excel\Concerns\WithUpsertColumns`| Allows upsert columns definition. | [Upserting with specific columns](/3.1/imports/model.html#upserting-with-specific-columns) |
 |`Maatwebsite\Excel\Concerns\WithValidation`| Validates each row against a set of rules. | [Row Validation](/3.1/imports/validation.html) |
 |`Maatwebsite\Excel\Concerns\SkipsOnFailure`| Skips on validation errors. | [Row Validation](/3.1/imports/validation.html#skipping-failures) |
 |`Maatwebsite\Excel\Concerns\SkipsOnError`| Skips on database exceptions. | [Row Validation](/3.1/imports/validation.html#skipping-errors) |

3.1/imports/model.md

@@ -50,6 +50,25 @@ In the example above, if a user already exists with the same email, the row will
 All databases except SQL Server require the `uniqueBy` columns to have a "primary" or "unique" index.
 :::
 
+### Upserting with specific columns
+
+By default, `upsert`, in case of updating, will update all columns that match model's attributes. However, if you need to update only specific column(s) during `upsert`, you can also implement the `WithUpsertColumns` concern.
+
+```php
+class UsersImport implements ToModel, WithUpserts, WithUpsertColumns
+{
+    /**
+     * @return array
+     */
+    public function upsertColumns()
+    {
+        return ['name', 'role'];
+    }
+}
+```
+
+In this example, if a user already exists, only "name" and "role" columns will be updated.
+
 ## Skipping rows
 
 In case you want to skip a row, you can return null.