implement GRIDs

app/Models/Row.php

@@ -6,7 +6,7 @@ namespace App\Models;
  * Row in a data table
  *
  * @property int $id
- * @property string $data - JSONB
+ * @property string $data - JSONB, always containing _grid
  */
 class Row extends BaseModel
 {
@@ -16,4 +16,39 @@ class Row extends BaseModel
 
     protected $guarded = [];
     public $timestamps = false;
+
+    public function getGridAttribute() {
+        return $this->data->_grid;
+    }
+
+    public function setGridAttribute($value) {
+        $this->data->_grid = $value;
+    }
+
+    /**
+     * Allocate a single Global Row ID, application-unique.
+     *
+     * GRIDs are used to uniquely identify existing or proposed new rows,
+     * and are preserved after row modifications, to ensure change proposals have
+     * a clear target.
+     *
+     * @return int
+     */
+    public static function allocateGRID()
+    {
+        return \DB::selectOne("SELECT nextval('global_row_id_seq') AS grid;")->grid;
+    }
+
+    /**
+     * Allocate a block of Global Row IDs, application-unique.
+     *
+     * @see Row::allocateGRID()
+     *
+     * @return int[] first and last
+     */
+    public static function allocateGRIDs($count)
+    {
+        $last = \DB::selectOne("SELECT multi_nextval('global_row_id_seq', ?) AS last_grid;", [$count])->last_grid;
+        return [$last - $count + 1, $last];
+    }
 }