implement GRIDs

database/migrations/2018_08_01_204822_add_row_sequence_generator.php

@@ -0,0 +1,54 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class AddRowSequenceGenerator extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        // https://www.depesz.com/2008/03/20/getting-multiple-values-from-sequences/
+        DB::unprepared(/** @lang PostgreSQL */
+            <<<PGSQL
+CREATE OR REPLACE FUNCTION multi_nextval(use_seqname TEXT, use_increment INT4) RETURNS INT4 AS $$
+DECLARE
+    reply int4;
+BEGIN
+    perform pg_advisory_lock(20180801);
+    execute 'ALTER SEQUENCE ' || quote_ident(use_seqname) || ' INCREMENT BY ' || use_increment::text;
+    reply := nextval(use_seqname);
+    execute 'ALTER SEQUENCE ' || quote_ident(use_seqname) || ' INCREMENT BY 1';
+    perform pg_advisory_unlock(20180801);
+    return reply;
+END;
+$$ LANGUAGE 'plpgsql';
+PGSQL
+);
+        DB::unprepared('CREATE SEQUENCE global_row_id_seq START 0 MINVALUE 0;');
+        // We have to increment manually once before the above function can be used - that is because
+        // nextval will return the initial value the first time it's called, so it would not advance by
+        // the given step at all. This would give us negative values - not a problem in postgres without unsigned
+        // types, but it loooks bad.
+        DB::select("SELECT nextval('global_row_id_seq') as nv;");
+
+        // The multi_nextval() is concurrency-safe, except it can sometimes happen that
+        // nextval in other connection also increments by the bigger step. The only downside is "wasted IDs".
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        DB::unprepared('DROP FUNCTION IF EXISTS multi_nextval(TEXT, INT4);');
+        DB::unprepared('DROP SEQUENCE IF EXISTS global_row_id_seq;');
+    }
+}

database/migrations/2018_08_01_213353_make_grid_column_mandatory_in_rows_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class MakeGridColumnMandatoryInRowsTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        DB::unprepared("ALTER TABLE rows ADD CONSTRAINT grid_must_exist CHECK (data ? '_grid');");
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        DB::unprepared("ALTER TABLE rows DROP CONSTRAINT grid_must_exist;");
+    }
+}